HK1167754A - Sensor device - Google Patents

Abstract

A sensor device is provided with a voltage detection type sensor unit (20) for converting a physical quantity into a voltage value and outputting a voltage signal indicating the voltage value; a chopper amplifier unit (10) for generating a modulation signal by chopping the voltage signal output from the sensor unit with a predetermined chopping frequency, amplifying the modulation signal into an amplification signal, then demodulating the amplification signal and outputting it as an output signal; an integration unit (13) including an operational amplifier (14) for amplifying a voltage difference between a voltage at a non-inverting input terminal and a voltage at an inverting input terminal, an input resistor (R1) connected to the inverting input terminal of the operational amplifier and a capacitor (C1) connected between the inverting input terminal and an output terminal of the operational amplifier (14) and adapted to sample the output signal output from the chopper amplifier unit (10) at a predetermined sampling frequency and integrate the sampled output signal; and a digital conversion unit for converting the output signal integrated by the integration unit into a digital signal.

Description

Sensor device

Technical Field

The present invention relates to a sensor device for detecting a physical quantity.

Background

Conventionally, a sensor device having a sensor unit for converting a physical quantity into an electrical quantity is known. For example, the sensor unit is a thermocouple. The thermocouple measures the temperature of the object by absorbing infrared rays emitted from the object.

The thermocouple represents the amount of temperature change in the form of a voltage signal. For example, if the temperature change amount is 1 degree, the temperature change amount is expressed in the form of a voltage signal of a voltage value of 2.3 μ V.

Since the temperature change amount is expressed in the form of a voltage signal of a small voltage value, the voltage signal needs to be amplified with a high gain in order to accurately measure the temperature of the object using the voltage signal.

Thus, sensor devices conventionally include an amplifier. The amplifier has a function of receiving a voltage signal from a sensor unit such as a thermocouple and amplifying the voltage signal. However, the output from the amplifier may be mixed into the offset voltage and low frequency 1/f noise inherent in the amplifier.

A widely known chopping technique (chopping technology) is a technique for effectively removing offset voltage and low-frequency 1/f noise inherent in an amplifier. This is a technique for separating the offset voltage and 1/f noise part mixed in the process of the amplification process by the amplifier from the voltage signal. For example, chopping techniques are disclosed in patent documents 1 and 2 below.

Document 1 discloses the "Reliable High Quality Infrared sensor has Found a Way of automatic Climate Control (Reliable High Quality Infrared sensor Found Climate Control)", Roger Diels, Melexis products sheet, http:// www.melexis.com/Assets/Reliable _ High _ Quality _ In _ automatic _ Climate _ Control _3810.aspx.

Document 2 is "CMOS Chopper operational amplifier with Integrated Low-Pass Filter (a CMOS Chopper with Integrated Low-Pass Filter)", a.bakker and j.h. huijsing, Proceedings oft 23rd European Solid-State Circuits conference.1997ess CIRC' 97.

The chopping technique is explained in detail. The frequencies of the offset voltage and 1/f noise part are converted into a chopping frequency and its odd multiples, whereas the frequency of the voltage signal part representing the temperature variation is converted into a frequency of a low frequency band and is an even multiple of the pre-chopping frequency. In this way, the offset voltage and 1/f noise portion having the chopping frequency and its odd multiples can be removed by the low-pass filter.

Disclosure of Invention

Removing only the offset voltage and 1/f noise part having the chopping frequency and its odd-numbered multiples and removing only the voltage signal part indicating the temperature change and being in the low frequency band by the low-pass filter has the following problems.

The offset voltage and 1/f noise mixed during the amplification process exist in a very low frequency band. The offset voltage and 1/f noise present in such a frequency band are processed by the chopping technique to have a chopping frequency and its odd multiples. The voltage signal portion representing the temperature change is processed to have a frequency of a low frequency band.

A low-pass filter with a low cut-off frequency is necessary to accurately remove only the voltage signal portion representing the temperature variation. The cut-off frequency of the low-pass filter is represented by 1/(2 π RC), where R represents the resistance value and C represents the capacitance.

In order for the low-pass filter to be able to have a low cut-off frequency, the time constant represented by RC needs to be large. Therefore, any one of the resistance value and the capacitance needs to be large.

Generally, the constituent elements for chopping and the low-pass filter are mounted on a monolithic integrated circuit. However, for example, if the number of resistors is increased or a larger capacitor is used to increase the time constant of the low-pass filter, the circuit size of the low-pass filter increases. As a result, the circuit size of the sensor device increases.

In order to more accurately measure the temperature of the object, the digitizer may be arranged to convert the voltage signal component that has been passed through the low pass filter into a digital signal. Since the digitizer is composed of a plurality of constituent elements, the circuit size of the sensor device is further increased.

In order to solve the above-described problems, an object of the present invention is to provide a sensor device capable of removing a noise component mixed in the process of amplification processing while performing digital conversion without increasing the circuit size.

According to one aspect the present invention is directed to a sensor device comprising: a voltage detection type sensor unit for converting a physical quantity into a voltage value and outputting a voltage signal representing the voltage value; a chopper amplifier unit for generating a modulated signal by chopping the voltage signal output from the sensor unit at a predetermined chopping frequency, amplifying the modulated signal into an amplified signal, and then demodulating the amplified signal and outputting it as an output signal; an integration unit including an operational amplifier for amplifying a voltage difference between a voltage of the non-inverting input terminal and a voltage of the inverting input terminal, an input resistor connected to the inverting input terminal of the operational amplifier, and a capacitor connected between the inverting input terminal and the output terminal of the operational amplifier, and adapted to sample an output signal output from the chopper amplifier unit at a predetermined sampling frequency and integrate the sampled output signal; and a digital conversion unit for converting the output signal integrated by the integration unit into a digital signal.

Drawings

Figure 1 is a diagram showing a typical configuration of a sensor device according to one embodiment of the invention,

figure 2 is a diagram showing a typical configuration of a chopper amplifier unit,

figure 3 shows a graph showing a typical operation of a chopper amplifier unit,

figure 4 is a diagram showing a typical construction of an integrator,

figure 5 is a graph showing typical frequency characteristics of a chopper amplifier unit and an integrator,

figure 6 is a diagram showing another exemplary configuration of a sensor device according to an embodiment of the invention,

FIG. 7 is a functional block diagram of an exemplary controller, an

Fig. 8 is a timing chart showing a typical operation of the controller.

Detailed Description

A sensor device according to an embodiment of the present invention is explained below. Fig. 1 is a diagram showing a typical configuration of a sensor device. Fig. 2 is a diagram showing a typical configuration of a chopper amplifier unit. Fig. 3 shows a graph showing a typical operation of a chopper amplifier unit. Fig. 4 is a diagram showing a typical configuration of an integrator.

The sensor device 1 shown in fig. 1 includes a controller (control unit) 11. The controller 11 centrally controls the respective constituent elements described below. The sensor device 1 further includes a voltage detection type sensor unit 20, a chopper amplifier unit 10, and an AD conversion circuit (digital conversion unit) 12. The sensor unit 20 converts the physical quantity into a voltage value, and outputs a voltage signal representing the voltage value.

The chopper amplifier unit 10 includes a first chopper circuit 100, an operational amplifier 101, and a second chopper circuit 102. For example, the chopper amplifier unit 10 operates as shown in fig. 3.

In the chopper amplifier unit 10, the first chopper circuit 100 receives an input of the voltage signal Vin output from the sensor unit 20 (see fig. 1). The graph (a) shown in fig. 3 shows a typical frequency characteristic of the sensor unit 20. The sensor unit 20 outputs a voltage signal Vin representing the detected temperature change in the form of a voltage signal to the first chopper circuit 100. This voltage signal Vin is a signal in which the frequency in the frequency band in the graph (a) is lower than the chopping frequency fc. Then, the first chopper circuit 100 modulates the voltage signal Vin received from the sensor unit 20 by chopping the voltage signal Vin received from the sensor unit 20 at a predetermined chopping frequency fc.

Graph (b) shown in fig. 3 shows a typical frequency characteristic of the first chopper circuit 100. Upon receiving the voltage signal Vin output from the sensor unit 20, the first chopper circuit 100 chops the voltage signal Vin with a chopping frequency fc. As a result, as shown in graph (b), the voltage signal Vin is modulated into a voltage signal having the chopping frequency fc and its odd multiples.

Here, in the graph (b), the voltage value of the voltage signal Vin having a frequency that is an odd multiple of the chopping frequency fc is smaller than the voltage value of the voltage signal Vin having the chopping frequency fc, and the voltage value of the voltage signal Vin decreases as the odd multiple of the chopping frequency fc increases. The reason for this is as follows.

A rectangular wave having a chopping frequency fc is used to modulate a signal having a certain frequency by chopping the signal having the certain frequency with the chopping frequency fc. The rectangular wave is composed of a fundamental wave having a chopping frequency fc as a basic frequency and harmonics having frequencies of predetermined multiples of the basic frequency (chopping frequency fc). For example, when the duty ratio of the rectangular wave is 50%, a spectrum of frequencies in which harmonics exist at odd multiples of the fundamental frequency (chopping frequency fc) is obtained as the spectrum of such rectangular wave.

In the frequency spectrum of a rectangular wave, it is known that as the frequency of a harmonic increases, the value of the harmonic decreases. Therefore, in the frequency spectrum of the rectangular wave, the value of the harmonic decreases as increasing by an odd multiple from the fundamental frequency (chopping frequency fc).

When the voltage signal Vin is modulated using such a rectangular wave, a signal having such a waveform as if obtained by superimposing the rectangular wave on the voltage signal Vin is obtained. As a result, the chopping frequency fc in the signal and the components of its odd multiples are obtained as the modulation voltage signal Vin.

Therefore, the voltage value of the voltage signal Vin having the odd-numbered multiples of the chopping frequency fc is smaller than the voltage value of the voltage signal Vin having the chopping frequency fc, and the voltage value of the voltage signal Vin decreases as the odd-numbered multiples of the chopping frequency fc increase.

The operational amplifier 101 amplifies the voltage value of the modulated voltage signal Vin having the chopping frequency fc and its odd multiples. In this amplification process, the voltage signal Vin is mixed with an offset voltage and 1/f noise (hereinafter, referred to as a noise component) inherent in the operational amplifier 101. Such a noise component is generally located in a frequency band lower than the chopping frequency fc.

Graph (c) shown in fig. 3 shows a typical frequency characteristic of the operational amplifier 101. When the operational amplifier 101 receives the voltage signal Vin modulated to have the chopping frequency fc and its odd multiples in the first chopper circuit 100, the voltage signal Vin is amplified by a predetermined amplification factor. As a result, the voltage signal Vin modulated to have the chopping frequency fc and its odd multiples is amplified. As shown in the graph (c), the voltage signal Vin is mixed with a noise component in a frequency band lower than the chopping frequency fc.

The second chopper circuit 102 demodulates the output signal of the operational amplifier 101 and outputs it as an output signal Vout. Graph (d) shown in fig. 3 shows a typical frequency characteristic of the second chopper circuit 102. As shown in the graph (d), by the demodulation of the second chopper circuit 102, the voltage signal Vin amplified by the operational amplifier 101 becomes to have the same frequency as that at the time of output from the sensor unit 20.

On the other hand, the noise component in the low frequency band mixed in the process of the amplification process by the operational amplifier 101 has the chopping frequency fc and its odd-numbered multiples by the demodulation by the second chopper circuit 102.

Next, the AD conversion circuit 12 is explained. The AD conversion circuit 12 is composed of a so-called double integral type a/D converter. The AD conversion circuit 12 includes an integrator (integration unit) 13, a comparator 15, a CR oscillation circuit (oscillation unit) 16, and a counter 17.

As shown in fig. 1 and 4, the integrator 13 includes an operational amplifier 14, an input resistor R1, and a capacitor C1. The input resistor R1 is connected to the inverting input terminal 14A of the operational amplifier 14. A capacitor C1 is connected between the inverting input terminal 14A and the output terminal 14B of the operational amplifier 14. In the operational amplifier 14, the non-inverting input terminal 14C is grounded.

A switch SW1 is provided at the other end of the input resistor R1. The other end of the resistor R1 is switchably connected to the terminal "a" or "b" through a switch SW 1. The terminal "a" is connected to the chopper amplifier unit 10. The reference voltage Vref is applied to the terminal "b". The switch SW1 is controlled by the controller 11.

The integration process in the integrator 13 is summarized below. First, as the switch SW1 is connected to the terminal "a", integration of the output signal Vout output from the chopper amplifier unit 10 is started. At this time, the capacitor C1 is charged with the output signal Vout. The integrator 13 maintains this state for a predetermined period (hereinafter, referred to as a sampling period). The sampling period is a period during which the switch SW1 is connected to the terminal "a", and may also be referred to as a sampling time. Since the output signal Vout output from the chopper amplifier unit 10 is input to the inverting input terminal 14A during sampling, the voltage of the output signal from the integrator 13 falls.

At the elapse of the sampling period after the start of charging the capacitor C1, the controller 11 connects the switch SW1 with the terminal "b", and causes the counter 17 to start counting the clock pulses CLK 1. In this way, the reference voltage Vref (voltage having a polarity opposite to that of the output signal Vout) is applied to the other end of the input resistor R1. Since the capacitor C1 starts to be discharged in this way, the output voltage of the integrator 13 increases. When the output voltage of the integrator 13 reaches a certain voltage (e.g., the reference voltage Vref), the controller 11 causes the switch SW1 to be placed at a position not connected to both of the terminals "a" and "b", and stops the counting of the clock pulse CLK1 by the counter 17. In this way, the integration process by the integrator 13 is completed.

The operational amplifier 14 of the integrator 13 has a characteristic of decreasing the amplification factor as the frequency of the input signal increases when the frequency of the input signal exceeds a predetermined frequency. Therefore, the integrator 13 can have a function of decreasing the amplification factor as the frequency increases when the frequency of the output signal Vout input to the integrator 13 exceeds a predetermined frequency (for example, a frequency 1.5 times the sampling frequency). Therefore, if the frequency of the input signal is lower than the predetermined frequency, the input signal may pass, but as the frequency of the input signal increases beyond the predetermined frequency, the passing of the input signal becomes more difficult. In other words, the integrator 13 functions as a low-pass filter.

The comparator 15 is used to determine whether the output signal from the integrator 13 has reached a predetermined voltage (e.g., the reference voltage Vref). The comparator 15 compares the voltage value of the output signal from the integrator 13 with the reference voltage Vref. The controller 11 monitors whether the output voltage of the integrator 13 has reached a predetermined voltage (for example, the reference voltage Vref). When the output voltage of the integrator 13 reaches a predetermined voltage, the controller 11 terminates the integration process by the integrator 13.

After the capacitor C1 starts discharging, the counter 17 counts the number of pulses of the clock pulse CLK1 until the output signal of the integrator 13 reaches a predetermined voltage (reference voltage Vref). The number of pulses counted by the counter 17 is proportional to the voltage value of the voltage signal input to the integrator 13. In this way, the number of pulses counted by the counter 17 is output to the circuit of the subsequent stage as a digital signal indicating the temperature change.

The main effects of this embodiment are explained.

The operational amplifier has a characteristic of decreasing an amplification factor as the frequency of the input signal increases when the frequency of the input signal exceeds a predetermined frequency. Therefore, the integrator 13 can have a function of decreasing the amplification factor as the frequency of the received output signal increases when the frequency of the received output signal exceeds a predetermined frequency. Therefore, if the frequency of the input signal is lower than the predetermined frequency, the integrator 13 allows the input signal to pass through, but as the frequency of the input signal increases beyond the predetermined frequency, it becomes more difficult to pass through the input signal.

Since the integrator 13 performs the function of a low-pass filter in this way, it is not necessary to provide a low-pass filter separately. Further, the integrated value passing through the integrator 13 is converted into a digital signal through the AD conversion circuit 12. As described above, according to this embodiment, digital conversion can be performed by removing noise components mixed in the process of amplification processing without increasing the circuit size of the sensor device 1.

The CR oscillation circuit 16 is an oscillator including a capacitor and a resistor. The CR oscillation circuit 16 generates a clock pulse CLK1 for operating the chopper amplifier unit 10 and the integrator 13. Although the CR oscillation circuit 16 is provided in the AD conversion circuit 12 in fig. 1, it may be provided independently of the AD conversion circuit 12.

The counter 17 counts the number of clock pulses CLK1 output from the CR oscillation circuit 16 for a predetermined period. The predetermined period is a period until the voltage of the output signal of the integrator 13 reaches the reference voltage Vref after the discharge of the capacitor C1 is started by the control of the controller 11. The count value is output as a digital signal to a circuit of a subsequent stage. In this way, a digital signal having a value corresponding to the charged amount of the capacitor C1 is output. Here, the capacitor and the resistor of the CR oscillation circuit 16 have the same temperature characteristics as the input resistor R1 and the capacitor C1 of the integrator 13. The capacitor and the resistor of the CR oscillation circuit 16 have the same electrical characteristics as the input resistor R1 and the capacitor C1 of the integrator 13.

Since the AD conversion circuit 12 is configured as described above, the voltage signal output from the chopper amplifier unit 10 is integrated in the integrator 13, and a digital signal having a value corresponding to the integrated value is output.

As shown in fig. 4, the sensor device 1 includes a pulse width adjusting circuit 24. For example, the pulse width adjusting circuit 24 is provided in the controller 11. The clock pulse CLK1 output from the CR oscillation circuit 16 is divided into the clock pulse CLK2 by the frequency dividing circuit shown in fig. 1. The pulse width adjusting circuit 24 performs a predetermined process (not shown) upon receiving the clock pulse CLK2, thereby adjusting the frequency at which the switch SW1 of the integrator 13 is connected to the terminal "a". In this way, the pulse width adjusting circuit 24 functions as a sampling frequency adjuster, that is, adjusts the frequency at which the switch SW1 is connected to the terminal "a", and thus has a function of adjusting the sampling frequency representing the frequency of the integrator 13 to sample the output signal Vout from the chopper amplifier unit 10.

In this way, the sampling frequency at which the integrator 13 samples the output signal Vout from the chopper amplifier unit 10 can be adjusted by the pulse width adjustment circuit 24. Therefore, the sensor device 1 according to this embodiment has the following advantages.

As described above, in the integrator 13, when the frequency of the received output signal exceeds the predetermined frequency, the amplification factor decreases as the frequency of the received output signal Vout increases. The frequency is determined by the magnitude of the sampling frequency at or above which the amplification factor is reduced (see fig. 5). The horizontal axis represents the frequency of the output signal Vout input to the integrator 13, and the vertical axis represents the voltage of the output signal output from the integrator 13. In fig. 5, the amplification factor decreases at or above a predetermined frequency, which is a frequency 1.5 times the sampling frequency fs.

As a result, the integrator 13 functions as a low-pass filter that makes the passage of the output signal Vout input to the integrator 13 more difficult as the frequency of the output signal Vout increases beyond a certain frequency determined by the magnitude of the sampling frequency fs. Therefore, if the magnitude of the sampling frequency fs is determined, the integrator 13 can make it difficult for noise components having frequencies exceeding a certain frequency determined by the magnitude of the sampling frequency fs to pass through.

In the sensor device 1 according to this embodiment, the sampling frequency fs at which the integrator 13 samples the received output signal Vout is adjusted by the pulse width adjustment circuit 24. Therefore, it is possible to adjust the output of noise components in a certain frequency band included in the output signal Vout input to the integrator 13, wherein the output of those noise components should be difficult to pass through the integrator 13. Therefore, from noise components in a certain frequency band mixed in the output signal trying to pass through the integrator 13, those noise components having frequencies exceeding a certain frequency determined by the magnitude of the sampling frequency fs are removed. As a result, the ratio of the noise component to the signal passing through the integrator 13 can be adjusted.

The pulse width adjusting circuit 24 includes a time generating circuit 19 and a time modulating circuit 18. The time generation circuit 19 generates a reference signal SG1 by dividing the clock pulse CLK2, the clock pulse CLK2 being obtained by dividing the clock pulse CLK1 output from the clock source (the CR oscillation circuit 16 in this embodiment). The time adjustment circuit 18 adjusts the duration of the sampling period indicated by the pulse width of the reference signal SG1 by adjusting the pulse width of the reference signal SG 1. The reference signal SG1 is a reference signal having a pulse width indicating a sampling reference period serving as a basis (basis) when the duration of the sampling period is adjusted.

The time adjustment circuit 18 also extends the sampling period by increasing the pulse width of the reference signal SG1, and shortens the sampling period by decreasing the pulse width. In this way, the pulse width adjusting circuit 24 adjusts the sampling frequency fs represented by the reciprocal of the sampling period by adjusting the sampling period.

In the sensor device 1 configured as described above, the chopping period represented by the reciprocal of the chopping frequency and the sampling period represented by the reciprocal of the sampling frequency fs are synchronized.

The chopping frequency fc is n times the sampling frequency fs (where n is a natural number equal to or greater than 1). For example, the relationship between the chopping frequency fc and the sampling frequency fs is realized by adjusting the sampling frequency fs by the pulse width adjustment circuit 24. In fig. 5, the chopping frequency fc is twice the sampling frequency fs.

Since the chopping frequency fc and the sampling frequency fs have such a relationship, the following functions and effects are obtained.

Fig. 5 is a graph showing typical frequency characteristics of the chopper amplifier unit 10 and the integrator 13. In fig. 5, the shaded area is a sensor output of a frequency in the range of 0 to fn, and the sensor output is an output reflected as a digital output.

In fig. 5, the noise components existing in the low frequency band are those having the chopping frequency fc and its odd multiples by the chopper amplifier unit 10.

The frequency response of the integrator 13 is such that: when the frequency of the output signal input to the integrator 13 is increased from 0 to the sampling frequency fs, the voltage value of the signal output from the integrator 13 is decreased from the predetermined voltage value Vint to 0. Thereafter, each time the frequency of the output signal input to the integrator 13 becomes a natural number multiple of two or more of the sampling frequency fs, the voltage value of the signal output from the integrator 13 becomes 0. For example, patent document 2 also discloses the frequency response described above.

Due to the characteristics of the operational amplifier 14, the frequency response of the integrator 13 is such that: when the frequency of the input signal exceeds a predetermined frequency (a frequency that is 1.5 times the sampling frequency fs), the amplification factor becomes 1/10 every time the frequency of the input signal becomes 10 times higher. In FIG. 5, this is represented by "-20 dB/decade (dB/decade)".

According to the sensor device 1 of this embodiment, as described above, the chopping period and the sampling period are synchronized, and the chopping frequency is n times the sampling frequency (where n is a natural number equal to or greater than 1). Therefore, the chopping frequency fc and its odd-numbered multiples coincide with the sampling frequency fs and its multiples at which the voltage value of the output signal output from the integrator 13 becomes 0.

Therefore, even if a voltage signal having the chopping frequency fc or its odd-numbered multiple is input to the integrator 13, the voltage value of the output signal output from the integrator 13 becomes 0. Therefore, the noise component mixed in the voltage signal having the chopping frequency fc or its odd-numbered multiples is not reflected on the output signal from the integrator 13. As a result, noise components mixed in the voltage signal from the sensor unit 20 can be accurately removed.

Here, one feature of the embodiment is explained again. The integrator 13 includes a switch SW1 and thus has the same function as a sampling filter. The sampling filter is capable of adjusting the cut-off frequency according to the sampling frequency. In this embodiment, noise components having high frequencies and contained in the output signal output from the chopper amplifier unit 10 are removed by adjusting the sampling frequency, that is, the sampling period of the integrator 13. Further, in this embodiment, a signal to become a base for a digital signal is generated using the charge charged in the capacitor C1 of the integrator 13 during a predetermined sampling period. In other words, the output signal integrated by the integrator 13 is generated by discharging the capacitor C1 of the integrator 13 after the sampling period has elapsed. The above operation is controlled by the controller 11.

The controller 11 is summarized as follows. Fig. 7 is a functional block diagram of an example of the controller 11. Fig. 8 is a timing chart showing a typical operation of the controller 11. The controller 11 has a function as an integration control unit and includes a pulse width adjustment circuit 24, a transistor control signal generation circuit 31, and a chopper signal generation circuit 33.

The pulse width adjusting circuit 24 includes a time generating circuit 19 and a time adjusting circuit 18. The time generation circuit 19 generates a reference signal SG1 by dividing the clock pulse CLK2 output from the frequency division circuit 25 shown in fig. 1. The time adjustment circuit 18 adjusts the duration of the sampling period indicated by the pulse width of the reference signal SG1 by adjusting the pulse width. The signal output from the time adjustment circuit 18 is a pulse signal having a sampling frequency, and is referred to as a sampling signal SG 2.

The transistor control signal generation circuit 31 generates a control signal SG3 for the transistor Tra and a control signal SG4 for the transistor Trb based on the sampling signal SG 2. The switch SW1 shown in fig. 1 is constructed by transistors Tra and Trb.

The terminal "a" and the input resistor R1 are connected by turning on the transistor Tra and are disconnected by turning off the transistor Tra. In contrast, the terminal "b" and the input resistor R1 are connected by turning on the transistor Trb and are disconnected by turning off the transistor Trb.

When the sampling signal SG2 rises as shown in fig. 8 (time t1), the control signal SG3 for the transistor Tra switches the state of the transistor Tra from the off state to the on state by being switched from low to high. Thus, terminal "a" and input resistor R1 are connected to charge capacitor C1. Since the control signal SG4 for the transistor Trb is low at time t1, the transistor Trb is kept off. Thus, terminal "b" and input resistor R1 are disconnected. At time t1, charging of capacitor C1 is started, thereby starting the sampling period. Thus, the output signal Vout output from the chopper amplifier unit 10 is input to the inverting input terminal 14A shown in fig. 1.

The operational amplifier 14 has a characteristic of decreasing the amplification factor as the frequency of the input signal increases when the frequency of the input signal exceeds a predetermined value. In this embodiment, the operational amplifier 14 functions as a low-pass filter by using this characteristic thereof. Therefore, during the sampling period, the capacitor C1 is charged with a signal obtained by removing a noise component having a high frequency from the output signal output from the integrator 13.

When sampling signal SG2 falls (time t2), the sampling period ends. At time t2, the control signal SG3 for the transistor Tra is switched from high to low, and the control signal SG4 for the transistor Trb is switched from low to high. Therefore, the transistor Tra is switched from the on state to the off state, and the transistor Trb is switched from the off state to the on state. Therefore, the terminal "a" is disconnected from the input resistor R1, and the terminal "b" is connected to the input resistor R1, whereby the capacitor C1 starts discharging.

The counter 17 shown in fig. 1 counts the number of clock pulses CLK1 until the voltage V1 of the output signal of the integrator 13 reaches the reference voltage Vref after the capacitor C1 starts discharging. It is determined by the comparator 15 whether the voltage V1 has reached the reference voltage Vref. The number of pulses counted by the counter 17 is proportional to the voltage value of the voltage signal Vout input to the integrator 13. The number of pulses counted by the counter 17 is output to the circuit of the subsequent stage as a digital signal indicating a temperature change.

It is assumed that the voltage V1 of the output signal from the integrator 13 increases and reaches the same value as the reference voltage Vref at time t 3. At time t3, the controller 11 switches the state of the transistor Trb from the on state to the off state by switching the control signal SG4 for the transistor Trb from high to low. Therefore, the input resistor R1 becomes unconnected to both terminals "a" and "b".

At time t4, the sampling signal SG2 rises, whereby the control signal SG3 for the transistor Tra switches from low to high and the capacitor C1 starts charging. The temperature is calculated based on the digital output obtained by repeating the above operations.

The temperature is calculated by a timer of the AD conversion circuit 12. The timer measures time until the integration process is completed after the lapse of the sampling period in the count value, and the time measured in the count value is output as a digital signal.

On the other hand, the chopping-signal generating circuit 33 shown in fig. 7 generates a chopping signal SG5 for chopping based on the clock pulse CLK2 from the frequency dividing circuit 25. In this embodiment, the clock pulse CLK2 is directly used as the chopping signal SG 5. Since the chopping signal SG5 and the sampling signal SG2 are generated based on the clock pulse CLK2, they can be synchronized.

Next, the CR oscillation circuit (oscillation unit) 16 shown in fig. 1 is explained.

The CR oscillation circuit 16 is composed of a resistor and a capacitor, and generates a clock pulse CLK1 for operating the chopper amplifier unit 10 and the integrator 13. The CR oscillation circuit 16 outputs a clock pulse CLK1, one cycle of which is a time constant of CR, of the clock pulse CLK 1. The resistor and the capacitor of the CR oscillation circuit 16 have the same temperature characteristics as the input resistor R1 and the capacitor C1 of the integrator 13.

When the oscillation period of the CR oscillation circuit 16 (the period of the clock pulse CLK 1) becomes longer due to the influence of temperature, the pulse width of the sampling signal SG2 becomes longer, and thus the sampling period becomes longer. Since this causes the charging time of the capacitor C1 to become longer, the amplification factor of the integrator 13 increases.

The amplification factor in the integrator 13 that operates on the pulses by the CR oscillation circuit 16 is determined by the ratio of the resistance value of the resistor of the CR oscillation circuit 16 to the resistance value of the input resistor R1 of the integrator 13. The amplification factor in the integrator 13 may also be determined by the ratio of the capacitance of the capacitor of the CR oscillation circuit 16 to the capacitance of the capacitor C1 of the integrator 13.

The resistor and the capacitor of the CR oscillation circuit 16 have the same temperature characteristics as the input resistor R1 and the capacitor C1 of the integrator 13. Therefore, when the internal temperature of the sensor device 1 changes, the resistance values of the CR oscillation circuit 16 and the integrator 13 change by the same amount, and the capacitances of the CR oscillation circuit 16 and the integrator 13 change by the same amount.

As a result, even if the internal temperature of the sensor device 1 changes, the ratio of the resistance value of the resistor of the CR oscillation circuit 16 to the resistance value of the input resistor R1 of the integrator 13 and the ratio of the capacitance of the capacitor of the CR oscillation circuit 16 to the capacitance of the capacitor C1 of the integrator 13 do not change. Therefore, when the internal temperature of the sensor device 1 changes, the change of the amplification factor in the integrator 13 can be suppressed.

The resistor and the capacitor of the CR oscillation circuit 16 have the same electrical characteristics as the input resistor R1 and the capacitor C1 of the integrator 13.

As described above, the amplification factor in the integrator 13 that operates on the pulses by the CR oscillation circuit 16 is determined by the ratio of the resistance value of the resistor of the CR oscillation circuit 16 to the resistance value of the input resistor R1 of the integrator 13. The amplification factor in the integrator 13 may also be determined by the ratio of the capacitance of the capacitor of the CR oscillation circuit 16 to the capacitance of the capacitor C1 of the integrator 13.

The resistor and the capacitor of the CR oscillation circuit 16 have the same electrical characteristics as the input resistor R1 and the capacitor C1 of the integrator 13. Here, the sheet resistance characteristics are cited as an example of the electrical characteristics.

Therefore, when a process variation occurs in the process of manufacturing the resistor of the CR oscillation circuit 16 and the input resistor R1 of the integrator 13, since the resistor of the CR oscillation circuit 16 and the input resistor R1 of the integrator 13 have the same electrical characteristics, the resistance value of the resistor of the CR oscillation circuit 16 and the resistance value of the input resistor R1 of the integrator 13 change by the same amount. Therefore, even if a process variation occurs in the process of manufacturing the resistor of the CR oscillation circuit 16 and the input resistor R1 of the integrator 13, the ratio of the resistance value of the resistor of the CR oscillation circuit 16 to the resistance value of the input resistor R1 of the integrator 13 does not change.

Further, when a process variation occurs in the process of manufacturing the capacitor of the CR oscillation circuit 16 and the capacitor C1 of the integrator 13, since the capacitor of the CR oscillation circuit 16 and the capacitor C1 of the integrator 13 have the same electrical characteristics, the capacitance of the capacitor of the CR oscillation circuit 16 and the capacitance of the capacitor C1 of the integrator 13 change by the same amount. Therefore, even if a process variation occurs in the process of manufacturing the capacitor of the CR oscillation circuit 16 and the capacitor C1 of the integrator 13, the ratio of the capacitance of the capacitor of the CR oscillation circuit 16 to the capacitance of the capacitor C1 of the integrator 13 does not change.

Therefore, even if a process variation occurs during the manufacturing of the resistor of the CR oscillation circuit 16 and the input resistance R1 of the integrator 13 or a process variation occurs during the manufacturing of the respective capacitors of the CR oscillation circuit 16 and the integrator 13, it is possible to suppress a change in the amplification factor in the integrator 13.

Next, another example of the configuration of the sensor device according to the embodiment of the present invention is explained. Fig. 6 is a diagram showing another example. The sensor device 1A further includes a short-circuit switch SW2, a first memory 21, a second memory 22, a changeover switch SW3, and a subtractor 23. When the short-circuit switch (cut-off portion) SW2 is turned on, two signal lines L connecting the sensor unit 20 and the chopper amplifier unit 10 are short-circuited.

A first memory (first storage) 21 and a second memory (second storage) 22 are provided at the subsequent stages of the AD conversion circuit 12. The changeover switch (selector SW3) selects which of the first memory 21 and the second memory 22 the data of the output signal from the AD conversion circuit 12 is stored in. The changeover switch SW3 switches the connection of the AD conversion circuit 12 to the first memory 21 and the second memory 22.

A subtractor 23 is provided at a subsequent stage of the first and second memories 12, 22, the subtractor 23 being configured to calculate a difference between the data of the output signal read out from the first memory 21 and the data of the output signal read out from the second memory 22.

In the sensor device 1A, the controller 11 (see fig. 1) cuts off the output of the voltage signal from the sensor unit 20 to the chopper amplifier unit 10 by setting the short-circuit switch SW2 in a closed state. On the other hand, the controller 11 permits the voltage signal from the sensor unit 20 to be input to the chopper amplifier unit 10 by setting the short-circuit switch SW2 in the open state.

The controller (control unit) 11 connects the AD conversion circuit 12 to the first memory 21 by switching the changeover switch SW3 to the first memory 21 side. On the other hand, the controller 11 connects the AD conversion circuit 12 to the second memory 22 by switching the switch SW3 to the second memory 22 side.

In the sensor device 1A thus configured, the controller 11 causes the digital signal from the AD conversion circuit 12 to be stored in the first memory 21 with the output of the voltage signal from the sensor unit 20 to the chopper amplifier unit 10 cut off.

At this time, since the two signal lines L connecting the sensor unit 20 and the chopper amplifier unit 10 are short-circuited, the voltage value represented by the voltage signal input to the chopper amplifier unit 10 is determined by the voltage drop caused by the impedance inherent in the sensor unit 20. Then, during the amplification process in the operational amplifier 101 of the chopper amplifier unit 10, the voltage signal is input to the chopper amplifier unit 10, and noise components inherent in the operational amplifier 101 are mixed. Therefore, the output signal from the chopper amplifier unit 10 is an output signal including a noise component.

Then, the voltage signal including the noise component is input from the chopper amplifier unit 10 to the AD conversion circuit 12. Since the voltage signal including the noise component is integrated by the integrator 13 in the AD conversion circuit 12, not only the noise component inherent in the operational amplifier 101 but also the noise component inherent in the operational amplifier 14 of the integrator 13 are reflected on the integrated value of the integrator 13. Therefore, noise components inherent in the operational amplifier 101 of the chopper amplifier unit 10 and the operational amplifier 14 of the integrator 13 are reflected in the digital signal from the AD conversion circuit 12.

Therefore, the data of the digital signal stored in the first memory 21 in the state where the flow of the voltage signal from the sensor unit 20 to the chopper amplifier unit 10 is cut off is the data of the digital signal reflecting the noise component inherent in the operational amplifier 101 of the chopper amplifier unit 10 and the operational amplifier 14 of the integrator 13.

On the other hand, the controller 11 causes the digital signal from the AD conversion circuit 12 to be stored in the second memory 22 without cutting off the flow of the voltage signal from the sensor unit 20 to the chopper amplifier unit 10. In other words, the controller 11 causes the data of the digital signal from the AD conversion circuit 12 to be stored in the second memory 22 while setting the short-circuit switch SW2 in the open state so that the two signal lines L are not short-circuited.

At this time, since the flow of the voltage signal from the sensor unit 20 to the chopper amplifier unit 10 is not cut off, a voltage signal including a noise component inherent in the operational amplifier 101 and indicating a temperature change is input from the chopper amplifier unit 10 to the AD conversion circuit 12.

Since the voltage signal including the noise component and indicating the temperature change is integrated by the integrator 13 in the AD conversion circuit 12, the integrated value of the integrator 13 reflects the noise component inherent in the operational amplifier 101 and the noise component inherent in the operational amplifier 14 of the integrator 13 in addition to the voltage signal indicating the temperature change. Therefore, the digital signal from the AD conversion circuit 12 reflects noise components inherent in the operational amplifier 101 of the chopper amplifier unit 10 and the operational amplifier 14 of the integrator 13, in addition to the voltage signal indicating the temperature change.

The controller 11 causes the subtractor 23 to calculate a difference between the data of the digital signal stored in the first memory 21 and the data of the digital signal stored in the second memory 22. As such, the digital signal representing the noise component becomes 0 by subtraction, and only the digital signal representing the temperature change remains.

In another example of the embodiment, in the case where the cut-off voltage signal is output from the sensor unit 20 to the chopper amplifier unit 10, data of the output signal from the AD conversion circuit 12 is stored in the first memory 21. Further, in the case where the output of the voltage signal from the sensor unit 20 to the chopper amplifier unit 10 is not cut off, the output signal from the AD conversion circuit 12 is stored in the second memory 22. Then, a difference between the data of the output signal stored in the first memory 21 and the data of the output signal stored in the second memory 22 is calculated.

As such, the difference between the digital signal including the noise component and representing the temperature change and the digital signal representing only the noise component is calculated. Therefore, noise components inherent in the sensor device 1A can be removed from the digital signal representing the temperature change, and thus the temperature of the object can be measured more accurately.

Further, the controller 11 performs such control as: the data of the output signal converted into the digital signal in the AD conversion circuit 12 is stored in the second memory 22 more frequently than the data of the output signal is stored in the first memory 21.

Specifically, the controller 11 sets the short switch SW2 in the open state and positions the changeover switch SW3 at the second memory 22 side more frequently than it sets the short switch SW2 in the closed state and positions the changeover switch SW3 at the first memory 21 side. Therefore, the signal line L connecting the sensor unit 20 and the chopper amplifier unit 10 can be less short-circuited. This makes it possible to shorten the period during which the load on the sensor device 1A is increased by short-circuiting the two signal lines connecting the sensor unit 20 and the chopper amplifier unit 10.

In particular, at the time of startup of the sensor device 1A, the controller 11 may cause the data of the output signal converted into the digital signal in the AD conversion circuit 12 to be stored in the first memory 21 only once. Thereafter, the controller 11 may maintain a state in which data of the output signal converted into the digital signal in the AD conversion circuit 12 is stored in the second memory 22. This process has the following advantages.

Specifically, at the time of activation of the sensor device 1A, the controller 11 sets the short-circuit switch SW2 in the off state and positions the changeover switch SW3 at the first memory 21 side only once. Thereafter, the controller 11 maintains a state in which the short switch SW2 is set in an open state and the changeover switch SW3 is disposed at the second memory 22 side.

Therefore, at the time of startup of the sensor device 1A, not the data of the digital signal of the voltage signal representing the temperature change, but the data of the digital signal reflecting the noise component is stored in the first memory 21. Thereafter, data of the digital signal reflecting the noise component and the voltage signal representing the temperature change are continuously stored in the second memory 22.

As a result, the difference between the data of the digital signal reflecting the noise component and the data of the digital signal which is continuously updated thereafter and reflects the noise component and the voltage signal representing the temperature change is obtained by the subtractor 23.

By the controller 11 performing the above-described processing, the chopper amplifier unit 10 and the AD conversion circuit 12 process the voltage signal representing the noise component only at the time of startup of the sensor device 1A, and thereafter process the voltage signal representing the temperature change other than the noise component, respectively.

As a result, the sensor device 1A can obtain a digital signal having a noise component removed therefrom while causing the chopper amplifier unit 10 and the AD conversion circuit 12 to collectively process voltage signals representing temperature changes other than the noise component. Therefore, the sensor device 1A can obtain a digital signal having a noise component removed therefrom while effectively utilizing the chopper amplifier unit 10 and the AD conversion circuit 12 originally designed to obtain a voltage signal representing a temperature change as a digital signal.

The controller 11 may perform the following processing. With the short-circuit switch SW2 set in the off state and the changeover switch SW3 disposed on the first memory 21 side, data of the digital signal reflecting the noise component is regularly stored in the first memory. Except for the period during which this process is performed, with the short-circuit switch SW2 set in the open state and the changeover switch SW3 disposed on the second memory 22 side, data of digital signals reflecting the noise component and the voltage signal representing the temperature change are successively stored in the second memory 22.

In this manner, the sensor device 1A regularly stores the data of the digital signal reflecting the noise component in the first memory 21, and sequentially stores the data of the digital signal reflecting the noise component and the voltage signal indicating the temperature change in the second memory 22 except for the period of performing the processing.

As described above, since the sensor device 1A has the data of the digital signal reflecting the noise component regularly stored in the first memory 21, even if the voltage value of the noise component changes due to a change in the internal temperature of the sensor device 1A, the data of the digital signal reflecting the noise component whose voltage value has changed is stored in the first memory 21.

The sensor device 1A causes data of the digital signal reflecting the noise component and the voltage signal representing the temperature change to be successively stored in the second memory 22, except for the period in which the data of the digital signal reflecting the noise component is stored in the first memory 21. Therefore, even if the voltage value of the noise component changes due to a change in the internal temperature of the sensor device 1A, data of a digital signal reflecting the noise component whose voltage value has changed and the voltage signal representing a temperature change is stored in the second memory 22.

As a result, in the sensor device 1A, the difference between the data of the digital signal reflecting the noise component whose voltage value has changed and the voltage signal representing the temperature change is obtained by the subtractor 23. Therefore, the sensor device 1A can obtain a digital signal having the noise component removed therefrom regardless of the change in the voltage value of the noise component.

The invention is summarized below.

A sensor device according to one aspect of the invention includes: a voltage detection type sensor unit for converting a physical quantity into a voltage value and outputting a voltage signal representing the voltage value; a chopper amplifier unit for generating a modulated signal by chopping the voltage signal output from the sensor unit at a predetermined chopping frequency, amplifying the modulated signal into an amplified signal, and then demodulating the amplified signal and outputting it as an output signal; an integration unit including an operational amplifier for amplifying a voltage difference between a voltage of the non-inverting input terminal and a voltage of the inverting input terminal, an input resistor connected to the inverting input terminal of the operational amplifier, and a capacitor connected between the inverting input terminal and the output terminal of the operational amplifier, and adapted to sample an output signal output from the chopper amplifier unit at a predetermined sampling frequency and integrate the sampled output signal; and a digital conversion unit for converting the output signal integrated by the integration unit into a digital signal.

According to this configuration, the integration unit including at least the operational amplifier is provided.

The operational amplifier has a characteristic of decreasing an amplification factor as the frequency of the input signal increases when the frequency of the input signal exceeds a predetermined frequency. Therefore, the integration unit can have a function of decreasing the amplification factor as the frequency of the received output signal increases when the frequency of the received output signal exceeds a predetermined frequency. By providing this function, if the frequency of the input signal is equal to or lower than the predetermined frequency, the integration unit permits the input signal to pass through while making the passing of the input signal more difficult as the frequency of the input signal increases beyond the predetermined frequency.

Therefore, the integration unit can perform a function as a low-pass filter without separately providing a low-pass filter. The integration value passing through the integration unit is converted into a digital signal by a digital conversion unit. Therefore, the sensor device can be configured to be capable of digital conversion while removing noise components mixed in the process of amplification processing without increasing the circuit size of the sensor device.

In the above configuration, a sampling frequency adjusting unit for adjusting the sampling frequency may be further provided.

As above, in the integration unit, when the frequency of the received output signal exceeds the predetermined frequency, the amplification factor decreases as the frequency of the received output signal increases. The predetermined frequency is determined by the magnitude of the sampling frequency, and the amplification factor is reduced at or above the predetermined frequency.

As a result, the integration unit functions as a low pass filter that makes the passing of the received output signal more difficult as the frequency of the output signal increases beyond a certain frequency determined by the magnitude of the sampling frequency. Therefore, if the magnitude of the sampling frequency is determined, the integration unit can make it more difficult for noise components having frequencies above a certain frequency determined by the magnitude of the sampling frequency to pass through.

According to this configuration, the sampling frequency is adjusted by the sampling frequency adjusting unit. Therefore, from noise components in a certain frequency band included in the output signal input to the integration unit, frequencies that are difficult to pass through the integration unit can be adjusted. Therefore, from noise components in a certain frequency band that are mixed in an output signal that is attempted to pass through the integration unit, those noise components having frequencies that exceed a certain frequency determined by the magnitude of the sampling frequency can be removed. As a result, the ratio of noise components in the signal passing through the integration unit can be adjusted.

In the above configuration, the chopping period and the sampling period may be synchronized, and the chopping frequency may be n times the sampling frequency (where n is a natural number equal to or greater than 1).

When the frequency of the output signal input to the integrator (integration unit) is increased from 0 to the sampling frequency, the voltage value of the signal output from the integrator is decreased from a predetermined voltage value to 0. Thereafter, every time the frequency of the output signal input to the integrator becomes twice the sampling frequency or a multiple of a natural number more, the voltage value of the signal output from the integrator becomes 0. In other words, the voltage value of the signal output from the integrator becomes 0 each time the frequency of the output signal input to the integrator becomes a multiple sampling frequency (see the above-mentioned document 2 and fig. 5).

The noise component mixed into the voltage signal during the amplification process of the chopper amplifier unit becomes an amplified signal having the chopping frequency and its odd-numbered multiples.

According to this configuration, the chopping period and the sampling period are synchronized and the chopping frequency is n times the sampling frequency (where n is a natural number equal to or greater than 1). Therefore, the chopping frequency and its odd-numbered multiples coincide with the sampling frequency at which the voltage value of the output signal output from the integrator becomes 0 and its multiples.

Therefore, even if a voltage signal having the chopping frequency and its odd-numbered multiples is input to the integrator (integrating unit), the voltage value of the output signal output from the integrator becomes 0. Therefore, the noise component mixed in the voltage signal having the chopping frequency or its odd-numbered multiples is not reflected on the output signal from the integrator.

Therefore, noise components mixed in the voltage signal from the sensor signal can be accurately removed.

In the above configuration, the sensor device may further include an oscillation unit including a CR oscillation circuit having a resistor and a capacitor for generating a clock pulse which is used for driving the chopper amplifier unit and the integration unit and which serves as a basis of a pulse signal (sampling signal) having a sampling frequency, and the resistor and the capacitor of the oscillation unit may have the same temperature characteristics as the input resistance and the capacitor of the integration unit.

The amplification factor in the integrating unit operating on the pulse by the oscillating unit is determined by the ratio of the resistance value of the resistor of the oscillating unit to the resistance value of the input resistor of the integrating unit. The amplification factor in the integration unit may also be determined by the ratio of the capacitance of the capacitor of the oscillation unit to the capacitance of the capacitor of the integration unit.

According to this configuration, the resistor and the capacitor of the oscillation unit have the same temperature characteristics as the input resistance and the capacitor of the integration unit. Therefore, when the internal temperature of the sensor device changes, the resistance values of the oscillation unit and the integration unit change by the same amount and the capacitances of the oscillation unit and the integration unit change by the same amount.

As a result, even if the internal temperature of the sensor device changes, the ratio of the resistance value of the resistor of the oscillation unit to the resistance value of the input resistor of the integration unit and the ratio of the capacitance of the capacitor of the oscillation unit to the capacitance of the capacitor of the integration unit do not change. Therefore, when the internal temperature of the sensor device changes, the change of the amplification factor in the integration unit can be suppressed.

In the above configuration, the sensor device may further include an oscillation unit including a CR oscillation circuit composed of a resistor and a capacitor for generating a clock pulse which is used for driving the chopper amplifier unit and the integration unit and which serves as a basis of a pulse signal (sampling signal) having a sampling frequency, and the resistor and the capacitor of the oscillation unit have the same electrical characteristics as the input resistance and the capacitor of the integration unit.

As described above, the amplification factor in the integration unit that operates on the pulse by the oscillation unit is determined by the ratio of the resistance value of the resistor of the oscillation unit to the resistance value of the input resistor of the integration unit. The amplification factor in the integration unit may also be determined by the ratio of the capacitance of the capacitor of the oscillation unit to the capacitance of the capacitor of the integration unit.

According to this configuration, the resistor and the capacitor of the oscillation unit have the same electrical characteristics as the input resistance and the capacitor of the integration unit. Here, an example in which the sheet resistance characteristic acts on the electric characteristic is cited.

Therefore, when a process variation occurs in the process of manufacturing the resistor of the oscillation unit and the input resistor of the integration unit, since the resistor of the CR oscillation circuit and the input resistor of the integration unit have the same electrical characteristics, the resistance value of the resistor of the CR oscillation circuit and the resistance value of the input resistor of the integration unit change by the same amount. Therefore, even if a process variation occurs during the manufacturing of the resistor of the CR oscillation circuit and the input resistance of the integration unit, the ratio of the resistance value of the resistor of the CR oscillation circuit to the resistance value of the input resistor of the integration unit does not change.

Further, when a process variation occurs in the process of manufacturing the capacitor of the CR oscillation circuit and the capacitor of the integration unit, since the capacitor of the CR oscillation circuit and the capacitor of the integration unit have the same electrical characteristics, the capacitance of the capacitor of the CR oscillation circuit and the capacitance of the capacitor of the integration unit are changed by the same amount. Therefore, even if a process variation occurs in the process of manufacturing the capacitor of the CR oscillation circuit and the capacitor of the integration unit, the ratio of the capacitance of the capacitor of the CR oscillation circuit to the capacitance of the capacitor of the integration unit is not changed.

Therefore, even if a process variation occurs during the manufacturing of the resistor of the CR oscillation circuit and the input resistor of the integration unit or a process variation occurs during the manufacturing of the respective capacitors of the CR oscillation circuit and the integration unit, it is possible to suppress a change in the amplification factor in the integration unit.

In the above configuration, the sensor device may further include a first memory and a second memory for storing data of the output signal of the digital signal converted in the digital conversion unit; a cut-off section for cutting off an output of the voltage signal from the sensor unit to the chopper amplifier unit; a selector for selecting one of the first memory and the second memory to store data of the output signal from the digital conversion unit; a control unit that, in a case where the cut-off section is caused to cut off the output of the voltage signal from the sensor unit to the chopper amplifier unit and the selector is caused to select the storage of the data of the output signal from the digital conversion unit in the first memory, causes the data of the output signal converted into the digital signal in the digital conversion unit to be stored in the first memory, and in a case where the cut-off section is caused not to cut off the output of the voltage signal from the sensor unit to the chopper amplifier unit and the selector is caused to select the storage of the data of the output signal from the digital conversion unit in the second memory, causes the data of the output signal converted into the digital signal in the digital conversion unit to be stored in the second memory; and a subtractor for calculating a difference between the data of the output signal stored in the first memory and the data of the output signal stored in the second memory.

According to this configuration, as the output of the voltage signal from the sensor unit to the chopper amplifier unit is cut off, data of the output signal from the digital conversion unit is stored in the second memory 22. Further, the output signal from the digital conversion unit is stored in the second memory without the output of the voltage signal from the sensor unit to the chopper amplifier unit being cut off. Then, a difference between the data of the output signal stored in the first memory and the data of the output signal stored in the second memory is calculated.

This makes it possible to calculate the difference between the digital signal having the noise component mixed therein and representing the temperature change and the digital signal representing only the noise component. Accordingly, it is possible to obtain a temperature measuring device having a digital signal from which noise components inherent in the sensor device are removed and which represents a temperature change, and thus capable of measuring the temperature of an object more accurately.

In the above configuration, the sensor unit and the chopper amplifier unit may be connected by a plurality of signal lines for transmitting voltage signals from the sensor unit; the cut-off part may be a short-circuit switch for short-circuiting the plurality of signal lines; the selector may be a switch for connecting any one of the first and second memories to the digital conversion unit; and the control unit can control the selector and the cut-off portion so that the data of the output signal converted into the digital signal in the digital conversion unit is stored in the second memory more frequently than in the first memory.

According to this configuration, the selector and the cut-off section are controlled so that the output signal is stored in the second memory more frequently than in the first memory. Therefore, the output signal from the digital conversion unit is stored in the second memory more frequently than the output signal from the digital conversion unit is stored in the first memory as the output of the voltage signal from the sensor unit to the chopper amplifier unit is cut off, without the output of the voltage signal from the sensor unit to the chopper amplifier unit being cut off.

Therefore, a state in which the output of the voltage signal from the sensor unit to the chopper amplifier unit is cut off occurs less frequently than a state in which the output of the voltage signal from the sensor unit to the chopper amplifier unit is not cut off.

As a result, the plurality of signal lines connecting the sensor unit and the chopper amplifier unit can be less short-circuited, and therefore an increase in load on the sensor device caused by short-circuiting the signal lines connecting the sensor unit and the chopper amplifier unit is suppressed.

In the above configuration, the sensor device may further include an integration control unit; the integration control unit may perform control to let the operational amplifier charge the capacitor by inputting the output signal output from the chopper amplifier unit to the inverting input terminal during a predetermined sampling period in each sampling period that is the reciprocal of the sampling frequency, and to discharge the capacitor after the lapse of the sampling period, so that the output signal integrated by the integration unit may be generated, and perform control to terminate the integration process when the voltage of the output signal output from the chopper amplifier unit reaches a predetermined reference voltage; and the digital conversion unit may include a timer for measuring a time until the integration process is ended after a sampling period of the digital value elapses, and outputting the measured time of the digital value as the digital signal.

This configuration is a specific configuration of the sensor device according to an aspect of the present invention. Therefore, the effects brought by the sensor device according to one aspect of the present invention can be achieved.

In the above configuration, the integration control unit may discharge the capacitor by applying a reference voltage having a polarity opposite to a polarity of a voltage of the output signal output from the chopper amplifier unit to the inverting input terminal after the lapse of the sampling period.

According to this configuration, since the reference voltage having the polarity opposite to the polarity of the voltage of the output signal output from the chopper amplifier unit is applied to the inverting input terminal, the capacitor of the integration control unit can be discharged.

In the above configuration, the sensor device may further include an oscillation unit including a CR oscillation circuit composed of a resistor and a capacitor, the CR oscillation circuit being configured to generate a clock pulse, the clock pulse being used to drive the chopper amplifier unit and the integration unit and serving as a basis for a pulse signal having a sampling frequency; the resistor and the capacitor of the oscillation unit have the same temperature characteristics as the input resistance and the capacitor of the integration unit; and the integration control unit may control charging and discharging of the capacitor of the operational amplifier based on the pulse signal.

According to this configuration, the effect brought about by the above-described feature that the resistor and the capacitor of the oscillation unit have the same temperature characteristics as the input resistance and the capacitor of the integration unit can be obtained.

In the above configuration, the sensor device may further include an oscillation unit including a CR oscillation circuit composed of a resistor and a capacitor for generating a clock pulse which is used for driving the chopper amplifier unit and the integration unit and which serves as a basis for a pulse signal having a sampling frequency; the resistor and the capacitor of the oscillation unit have the same electrical characteristics as the input resistance and the capacitor of the integration unit; and the integration control unit controls charging and discharging of the capacitor of the operational amplifier based on the pulse signal.

According to this configuration, the effect brought about by the above-described feature that the resistor and the capacitor of the oscillation unit have the same electrical characteristics as the input resistance and the capacitor of the integration unit can be obtained.

Claims (11)

1. A sensor device, comprising:

a voltage detection type sensor unit for converting a physical quantity into a voltage value and outputting a voltage signal representing the voltage value;

a chopper amplifier unit that generates a modulated signal by chopping the voltage signal output from the sensor unit at a predetermined chopping frequency, amplifies the modulated signal into an amplified signal, and then demodulates and outputs the amplified signal as an output signal;

an integration unit including an operational amplifier for amplifying a voltage difference between a voltage of a non-inverting input terminal and a voltage of an inverting input terminal, an input resistor connected to the inverting input terminal of the operational amplifier, and a capacitor connected between the inverting input terminal and an output terminal of the operational amplifier, the integration unit being adapted to sample the output signal output from the chopper amplifier unit at a predetermined sampling frequency and integrate the sampled output signal; and

a digital conversion unit for converting the output signal integrated by the integration unit into a digital signal.

2. The sensor device of claim 1, further comprising a sampling frequency adjustment unit for adjusting the sampling frequency.

3. The sensor apparatus of claim 1, wherein:

a chopping period represented by the inverse of the chopping frequency and a sampling period represented by the inverse of the sampling frequency are synchronized; and is

The chopping frequency is n times the sampling frequency, where n is a natural number equal to or greater than 1.

4. The sensor device according to claim 1, further comprising an oscillation unit including a CR oscillation circuit having a resistor and a capacitor for generating clock pulses for driving the chopper amplifier unit and the integration unit and serving as a basis for a pulse signal having the sampling frequency, wherein:

the resistor and the capacitor of the oscillation unit have the same temperature characteristics as the input resistor and the capacitor of the integration unit.

5. The sensor device according to claim 1, further comprising an oscillation unit including a CR oscillation circuit having a resistor and a capacitor for generating clock pulses for driving the chopper amplifier unit and the integration unit and serving as a basis for a pulse signal having the sampling frequency, wherein:

the resistor and the capacitor of the oscillation unit have the same electrical characteristics as the input resistor and the capacitor of the integration unit.

6. The sensor apparatus of any one of claims 1 to 5, further comprising:

a first memory and a second memory for storing data of the output signal converted into the digital signal in the digital conversion unit;

a cut-off section for cutting off an output of the voltage signal from the sensor unit to the chopper amplifier unit;

a selector for selecting the first memory or the second memory to store the data of the output signal from the digital conversion unit;

a control unit that, in a case where the cut-off section is caused to cut off the output of the voltage signal from the sensor unit to the chopper amplifier unit and the selector is caused to select the data of the output signal from the digital conversion unit to be stored in the first memory, causing the data of the output signal converted into the digital signal in the digital conversion unit to be stored in the first memory, and in a case where the cut-off section is caused not to cut off the output of the voltage signal from the sensor unit to the chopper amplifier unit and the selector is caused to select the data of the output signal from the digital conversion unit to be stored in the second memory, causing the data of the output signal converted into the digital signal in the digital conversion unit to be stored in the second memory; and

a subtractor for calculating a difference between the data of the output signal stored in the first memory and the data of the output signal stored in the second memory.

7. The sensor apparatus of claim 6, wherein:

the sensor unit and the chopper amplifier unit are connected by a plurality of signal lines for transmitting the voltage signals from the sensor unit;

the cutoff portion is a short-circuit switch for short-circuiting the plurality of signal lines;

the selector is a changeover switch for connecting any one of the first memory and the second memory to the digital conversion unit; and is

The control unit controls the selector and the cut-off section so that the data of the output signal converted into the digital signal in the digital conversion unit is stored in the second memory more frequently than in the first memory.

8. The sensor apparatus of claim 1, further comprising an integral control unit, wherein:

the integration control unit performs control to cause the operational amplifier to charge a capacitor by inputting the output signal output from the chopper amplifier unit to the inverting input terminal during a predetermined sampling period in each sampling period that is the reciprocal of the sampling frequency and to discharge the capacitor after the lapse of the sampling period, thereby generating the output signal integrated by the integration unit, and performs control to terminate an integration process when a voltage of the output signal output from the chopper amplifier unit reaches a predetermined reference voltage; and is

The digital conversion unit includes a timer for measuring a time until the integration processing is ended after the lapse of the sampling period of the digital value, and outputting the measured time of the digital value as the digital signal.

9. The sensor device according to claim 8, wherein the integration control unit discharges the capacitor by applying the reference voltage having a polarity opposite to a polarity of a voltage of the output signal output from the chopper amplifier unit to the inverting input terminal after the sampling period elapses.

10. The sensor device according to claim 8 or 9, further comprising an oscillation unit including a CR oscillation circuit having a resistor and a capacitor for generating clock pulses for driving the chopper amplifier unit and the integration unit and serving as a basis for a pulse signal having the sampling frequency, wherein:

the resistor and the capacitor of the oscillation unit have the same temperature characteristics as the input resistance and the capacitor of the integration unit; and is

The integration control unit controls charging and discharging of the capacitor of the operational amplifier based on the pulse signal.

11. The sensor device according to claim 8 or 9, further comprising an oscillation unit including a CR oscillation circuit having a resistor and a capacitor for generating clock pulses for driving the chopper amplifier unit and the integration unit and serving as a basis for a pulse signal having the sampling frequency, wherein:

the resistor and the capacitor of the oscillation unit have the same electrical characteristics as the input resistance and the capacitor of the integration unit; and is

The integration control unit controls charging and discharging of the capacitor of the operational amplifier based on the pulse signal.