JP2011091609A - Analog-digital conversion circuit, illuminance sensor, proximity sensor, cellular phone, digital camera - Google Patents

Abstract

An analog-digital conversion circuit, an illuminance sensor, a proximity sensor, a mobile phone, and a digital camera capable of setting a minimum resolution smaller than that of a conventional resolution without impairing measurement accuracy are provided.
A charging circuit 2 having a capacitor C1 for storing a charge corresponding to an input current, a discharging circuit 6 for discharging the charge stored in the capacitor C1, an output voltage of the charging circuit 2, and a reference voltage output by a voltage source V1 The comparison circuit 3 that compares vref, the switch SW1 that opens and closes between the output of the voltage source V1 and the output of the charging circuit 2, and the switch control circuit that outputs a switch control signal that controls opening and closing of the switch SW1 to the switch SW1 7, a control circuit 4 that outputs a digital value corresponding to the number of discharges from the comparison signal comp output from the comparison circuit 3, and a PWM control circuit 5 that performs pulse width modulation control on the discharge charge amount of the discharge circuit 6. .
[Selection] Figure 1

Description

  The present invention relates to an integral type analog-digital conversion circuit, an illuminance sensor, and a proximity sensor.

  The integration type analog-digital conversion circuit has a feature that a high-resolution can be realized with a simple configuration. This is suitable for a device such as an illuminance sensor that requires a low resolution but a high resolution (about 16 bits).

  As a conventional technique related to an analog-digital conversion circuit, a system described in Patent Document 1 has been proposed.

  It comprises a capacitor for storing charges according to the input voltage value, a constant current circuit for discharging the stored charges, and a counter for counting clock pulses from the start of discharge until the voltage across the capacitor reaches a constant value.

  As a conventional technique of an analog-digital conversion circuit relating to an illuminance sensor, a method described in Patent Document 2 has been proposed.

  A capacitor for storing an electric charge corresponding to an input current; and first and second discharge circuits for discharging the stored electric charge; charging the capacitor for a predetermined charging time; Every time the amount is reached, discharge is performed by the first discharge circuit. The charge after the end of the charging time is discharged by the second discharge circuit. Thus, a digital value corresponding to the charge amount of the capacity is output based on the number of discharges of the first discharge circuit and the number of discharges of the second discharge circuit.

  In a liquid crystal panel such as a cellular phone or a digital camera, there is a demand for mounting an illuminance sensor in order to control the amount of light emitted from a liquid crystal backlight according to the illuminance of disturbance. In addition, in liquid crystal panels such as mobile phones and digital cameras, there is an increasing demand for mounting a proximity sensor so as to be turned off when a face approaches due to low power consumption. In a portable device, a filter is provided in the sensor portion so as to make the sensor portion invisible from the outside of the design, so that incident light becomes small. Therefore, an illuminance sensor that can measure even lower illuminance and a proximity sensor that can be detected by a minute input signal are desired.

  Here, a circuit system for satisfying the above requirements will be described.

  FIG. 8 is a block diagram showing the configuration of the first conventional example. FIG. 8 corresponds to FIG.

  The analog-to-digital converter 101 in FIG. 8 includes a capacitor C that stores charges according to the value of the input voltage Vin, a constant current circuit 102 that discharges the stored charges, and a voltage across the capacitor C from a discharge start to a constant value. The counter 103 that counts the clock pulses until the time is reached and the control circuit 104 that controls the counter 103 are provided, and analog-digital conversion of the input voltage value is possible with a simple configuration.

  FIG. 9 is a block diagram showing the configuration of the second conventional example. FIG. 9 corresponds to FIG.

  The analog / digital converter 111 of FIG. 9 includes a capacitor C101 that stores charges according to an input current and discharge circuits 112 and 113 that discharge the stored charges, and charges the capacitor C101 for a predetermined charging time. At the same time, the discharge circuit 112 discharges the capacitor C101 every time it reaches a predetermined charge amount. By discharging the charge after the end of the charging time by the discharge circuit 113, a digital value corresponding to the charge amount of the capacitor C101 is output based on the number of discharges of the discharge circuit 112 and the number of discharges of the discharge circuit 113. The input dynamic range can be expanded, the minimum resolution can be improved, and the measurement time can be shortened. 9 performs charge / discharge control of the charge circuit 115 and the discharge circuits 112 and 113, calculates the total charge amount of the charge circuit 115 from the total number of discharges of the discharge circuits 112 and 113, and It is means for performing digital output according to the result.

  Here, the illuminance sensor generally uses a system in which light such as sunlight or fluorescent light is converted into a current by a photodiode and digitally output by an integration type analog-digital conversion circuit. In recent years, a proximity sensor that includes an integral type analog-digital conversion circuit and a light emitting diode drive circuit has been adopted.

FIG. 10 is a front view showing the configuration of the third conventional example. FIG. 10 shows a configuration of a general proximity sensor 121. The proximity sensor 121 includes a photodiode PD, a light emitting diode LED, and a control circuit 122. The light emitting diode LED is driven from the control circuit 122, converted into a current by the light receiving photodiode PD, and detected by the control circuit 122.

  FIG. 11A is a waveform diagram when the detected object 123 is close to a general proximity sensor 121. FIG. 11B is a waveform diagram when the detected object 123 is not in proximity to a general proximity sensor 121. The difference between the data (Data1) during the period when the light emitting diode is driven and the data (Data2) during the period when the light emitting diode is not driven is referred to as proximity data (Data1-Data2).

  When the detection object 123 is present, the reflected light from the detection object 123 is strong, so that the current of the photodiode PD increases, and the proximity data (Data 1 -Data 2) exceeds the threshold value Data_th of the control circuit 122. (FIG. 11 (a)).

  When the detection object 123 is not present, the reflected light 124 from the detection object 123 is weak, so that the current of the photodiode PD is small and the proximity data (Data 1 -Data 2) does not exceed the threshold value Data_th of the control circuit 122. (FIG. 11B).

Japanese Patent Laid-Open No. 2001-160756 (released on June 12, 2001) JP 2008-42886 (published February 21, 2008)

The analog-to-digital converter 101 of FIG. 8 as the first conventional example can perform analog-to-digital conversion of input voltage values with a simple configuration. Here, considering the resolution of the integral type analog-digital conversion circuit, the circuit operates so that the charge amount by the input signal and the discharge charge amount by the constant current circuit are balanced. Therefore, when the period of the clock signal clk is t_clk, the value obtained by counting the number of discharges is count, and the reference current value is I, the following expressions (A) and (B) are established.
Charge amount = Vin * C (A)
Discharge charge amount = I * t_clk * count (B)
From charge amount = discharge charge amount, the following equation (C) is established. From equation (C), the minimum resolution is determined by I * t_clk. Since t_clk is usually a constant value, the resolution is determined by the reference current value I of the constant current circuit.
count = (Vin * C) / (I * t_clk) (C)
In a portable device, a filter is provided in the sensor portion so as to make the sensor portion invisible from the outside of the design, so that incident light becomes smaller. When applied as an illuminance sensor that can measure even lower illuminance or a proximity sensor that can be detected by a minute input signal, it is necessary to configure the current value of the integral type analog-digital conversion circuit at a minute level (nA order). A minute current has a large error and causes a problem in measurement accuracy.

  The analog / digital converter 111 of FIG. 9 as the second conventional example can improve the input dynamic range and minimum resolution and shorten the measurement time with a configuration suitable for an illuminance sensor.

In the analog / digital converter 111, the circuit operates so that the charge amount by the input signal and the discharge charge amount by the constant current circuit are balanced. For this reason, the input current is Iin, the charging period is t_conv, the most significant bit (MSB: Most Significant Bit) of the counted value is counted_msb, and the least significant bit (LSB: Least Significant Bit) of the counted count Where count_lsb and the reference voltage value are Vref, the following equations (D) and (E) are established.
Charge amount = Iin * t_conv (D)
Discharge charge amount = C102 * Vref * count_msb + C103 * Vref / 2 * count_lsb (E)
From the charged charge amount = the discharged charge amount, the following equation (F) is established. From equation (F), the minimum resolution is determined by C103 * Vref / 2.
(2 * C102 / C103) * count_msb + count_lsb = (Iin * t_conv) / (C103 * Vref / 2) (F)
In a portable device, a filter is provided in the sensor portion so as to make the sensor portion invisible from the outside of the design, so that incident light becomes smaller. When applied as an illuminance sensor that can measure even lower illuminance or a proximity sensor that can be detected by a minute input signal, it is necessary to reduce the capacitance value or the reference voltage value of the integration type analog-digital conversion circuit. In the case of a semiconductor, a small capacitance value has a large error, causing a problem in measurement accuracy. When the voltage value is reduced, a problem occurs in the operating voltage range of the circuit.

  The proximity sensor 121 of FIG. 10 as the third conventional example can determine the proximity / non-proximity of an object. However, since the integration type analog-digital conversion circuit is used, the resolution is the conventional example 1 or This is the same as the method of Conventional Example 2. Therefore, the same problem as in Conventional Example 1 or Conventional Example 2 occurs.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an analog-to-digital conversion circuit capable of setting a minimum resolution smaller than the conventional resolution without impairing measurement accuracy, and illuminance. It is to provide a sensor, a proximity sensor, a mobile phone, and a digital camera.

  In order to solve the above-described problem, the analog-digital conversion circuit of the present invention is an integration type analog-digital conversion circuit that digitally converts and outputs the amount of input current, and charges according to the input current. A charging circuit having a capacity for storing; a discharging circuit for discharging the charge stored in the capacity; a comparison circuit for comparing an output voltage of the charging circuit with a reference voltage output by a voltage source; an output of the voltage source; and A switch that opens and closes the output of the charging circuit, a switch control circuit that outputs a switch control signal that controls opening and closing of the switch to the switch, and a digital that corresponds to the number of discharges from the comparison signal output from the comparison circuit A control circuit for outputting a value; and a pulse width modulation control circuit for performing pulse width modulation control on a discharge charge amount of the discharge circuit.

  According to the invention, when the operation of the analog-digital conversion circuit is started, the switch is closed by the switch control signal from the switch control circuit. For this reason, the output voltage of the charging circuit which is an integrating circuit is charged to the reference voltage. During the charging period (data conversion time), the switch is opened by a switch control signal from the switch control circuit, so that the capacitor is charged by the input current and converted from analog to digital.

  Further, the minimum resolution of the analog-digital conversion circuit can be adjusted by the duty ratio by the pulse width modulation control circuit without reducing the reference current value in the discharge circuit. Therefore, it is possible to provide an analog-digital conversion circuit capable of setting a minimum resolution smaller than that of the conventional one without impairing measurement accuracy.

  In the analog-digital conversion circuit, the pulse width modulation control circuit includes a delay circuit, first and second exclusive OR circuits, a D flip-flop, and a variable delay circuit. A clock signal is input to the input, a delay clock signal is output from the output of the delay circuit to the clock signal input of the D flip-flop, and a charge signal is applied to the first input of the first exclusive OR circuit. The output of the first exclusive OR circuit is connected to the input of the D flip-flop, and the second input of the first exclusive OR circuit is the output of the D flip-flop. Are connected to a first input of the second exclusive OR circuit and an input of the variable delay circuit, and an output signal is output from an output of the D flip-flop, and an output of the variable delay circuit is output. From the second input of the second exclusive OR circuit, the output from the delay output signal, may be output pulse width modulated signal from the output of the second exclusive OR circuit.

  The pulse width modulation control circuit counts the number of the delayed clock signals during the discharge period. Further, by adjusting the delay time in the delayed output signal by the variable delay circuit, the duty ratio can be adjusted by adjusting the pulse width of the pulse width modulation signal.

  In the analog-digital conversion circuit, the pulse width modulation control circuit includes a first delay circuit, first and second exclusive OR circuits, a D flip-flop, a second delay circuit, and a MOS transistor. A comparator, a variable current source, a variable capacitor and a variable voltage source, and the MOS transistor, the comparator, the variable current source, the variable capacitor, and the variable voltage source constitute a ramp circuit, and A clock signal is input to the input of the first delay circuit, a delayed clock signal is output from the output of the delay circuit to the clock signal input of the D flip-flop, and the first input of the first exclusive OR circuit Is supplied with a charge signal, and the output of the first exclusive OR circuit is connected to the input of the D flip-flop. Are connected to the output of the D flip-flop, the first input of the second exclusive OR circuit, and the input of the second delay circuit, and from the output of the D flip-flop, An output signal is output, a delayed output signal is output from the output of the second delay circuit to the second input of the second exclusive OR circuit, and from the output of the second exclusive OR circuit A trigger signal is output to the gate of the MOS transistor, the power supply voltage is applied to the input of the variable current source, and the output of the variable current source is the source of the MOS transistor, one end of the variable capacitor, and the comparator. A ramp signal is input to the inverting input terminal of the comparator, and the drain of the MOS transistor, the other end of the variable capacitor, and the variable voltage are connected to the inverting input terminal. Input is electrically grounded, the output of the variable voltage source is connected to the non-inverting input terminal of the comparator, pulse width modulated signal from the output of the comparator may be output.

  In the pulse width modulation control circuit, the number of the delayed clock signals is counted during the discharge period, the trigger signal which is a pulse signal is generated, and the pulse width of the pulse width modulation signal is adjusted in the ramp circuit to set the duty ratio. Can be adjusted.

  In the analog-digital conversion circuit, the time for delaying the output signal in the variable delay circuit may be increased or decreased.

  Thereby, since the delay time in the delayed output signal can be adjusted by the variable delay circuit, the duty ratio can be adjusted by adjusting the pulse width of the pulse width modulation signal.

  In the analog-digital conversion circuit, the current value of the variable current source, the capacitance value of the variable capacitor, or the voltage value of the variable voltage source may be increased or decreased.

  Accordingly, the duty ratio can be adjusted by adjusting the pulse width of the pulse width modulation signal in the ramp circuit.

  The illuminance sensor of the present invention includes a photodiode that receives light from the outside and converts it into a current, and any one of the analog-digital conversion circuits that receives a current output from the photodiode. Therefore, it is possible to measure even lower illuminance than before.

  The proximity sensor of the present invention includes a light emitting diode that emits light for detecting an object to be detected, a light emitting diode driving circuit that drives the light emitting diode, a photodiode that receives light from the outside and converts it into a current, and the photo diode. Any of the above-described analog-digital conversion circuits to which a current output from a diode is input is provided. Therefore, the detected object can be detected with a minute input signal.

  The mobile phone of the present invention includes a liquid crystal panel that displays a screen, a backlight that illuminates the liquid crystal panel, a backlight control unit that controls the luminance of the backlight, and the illuminance sensor or the proximity sensor. The backlight control unit controls the luminance of the backlight based on the output signal of the analog-digital conversion circuit.

  The digital camera of the present invention includes a liquid crystal panel that displays a screen, a backlight that illuminates the liquid crystal panel, a backlight control unit that controls the luminance of the backlight, and the illuminance sensor or the proximity sensor. And the backlight control unit controls the luminance of the backlight based on an output signal of the analog-digital conversion circuit.

  Thereby, even in a portable device (for example, a mobile phone or a digital camera) provided with a filter in the sensor portion in order to make the sensor portion invisible from the outside of the design, there is no problem in measurement accuracy.

  As described above, the analog-digital conversion circuit of the present invention includes a charging circuit having a capacity for storing electric charge according to an input current, a discharging circuit for discharging the electric charge stored by the capacity, and an output voltage of the charging circuit. A comparison circuit that compares a reference voltage output from the voltage source, a switch that opens and closes between the output of the voltage source and the output of the charging circuit, and a switch control signal that controls opening and closing of the switch is output to the switch A control circuit that outputs a digital value corresponding to the number of discharges from the comparison signal output from the comparison circuit, and a pulse width modulation control circuit that performs pulse width modulation control on the discharge charge amount of the discharge circuit; Is provided.

  Therefore, it is possible to provide an analog-digital conversion circuit that can set a minimum resolution smaller than the conventional resolution as well as an illuminance sensor, a proximity sensor, a mobile phone, and a digital camera without impairing measurement accuracy.

1 is a block diagram showing an integration type analog-digital conversion circuit according to an embodiment of the present invention. FIG. It is a wave form diagram showing operation of an integration type analog-digital conversion circuit concerning an embodiment of the present invention. It is a circuit diagram of the PWM control circuit which concerns on embodiment of this invention. It is a wave form diagram which shows operation | movement of the PWM control circuit which concerns on embodiment of this invention. It is a circuit diagram of the other PWM control circuit which concerns on embodiment of this invention. It is a wave form diagram which shows operation | movement of the other PWM control circuit which concerns on embodiment of this invention. (A) is a block diagram of a mobile phone according to an embodiment of the present invention, (b) is a block diagram of a digital still camera according to an embodiment of the present invention. It is a block diagram which shows the structure of a 1st prior art example. It is a block diagram which shows the structure of a 2nd prior art example. It is a front view which shows the structure of a 3rd prior art example. (A) is a waveform diagram when a detected object is close to a general proximity sensor, and (b) is a waveform diagram when a detected object is not close to a general proximity sensor.

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram showing an integral type analog-digital conversion circuit 1 according to an embodiment of the present invention. The analog-digital conversion circuit 1 generally includes a charging circuit 2, a comparison circuit 3, a control circuit 4, a PWM control circuit (pulse width modulation control circuit) 5, and a discharge circuit 6.

  The charging circuit 2 includes a capacitor C1 and a differential amplifier AMP1. The comparison circuit 3 includes a comparator CMP1, a switch SW1, a voltage source V1, and a switch control circuit 7. The voltage source V1 outputs a reference voltage vref. The control circuit 4 has a D flip-flop D-FF and a counter 8. The discharge circuit 6 includes a current source I1 and a switch SW2.

  In the analog-digital conversion circuit 1, the power supply voltage Vdd is applied to the input of the current source I1. The output of the current source I1 is connected to one end of the switch SW2. The other end of the switch SW2, one end of the capacitor C1, and the inverting input terminal (−) of the differential amplifier AMP1 are connected to each other and an input current Iin flows.

  The other end of the capacitor C1, the output of the differential amplifier AMP1, the non-inverting input terminal (+) of the comparator CMP1, and one end of the switch SW1 are connected to each other. An output voltage vsig is output from the output of the differential amplifier AMP1. The other end of the switch SW1 is connected to the inverting input terminal (−) of the comparator CMP1 and the output of the voltage source V1.

  The output of the comparator CMP1 is connected to the input of the D flip-flop D-FF. A comparison signal comp is output from the output of the comparator CMP1 (output of the comparison circuit 3). The output of the D flip-flop D-FF is connected to the input of the counter 8 and the input of the PWM control circuit 5. The pulse width modulation signal pwm for controlling the opening / closing of the switch SW2 is output from the output of the PWM control circuit 5 to the control input of the switch SW2.

  The non-inverting input terminal (+) of the differential amplifier AMP1 and the input of the voltage source V1 are electrically grounded.

  The analog-to-digital conversion circuit 1 is an analog-to-digital conversion circuit that digitally converts the current amount of the input current Iin and outputs it. The analog-to-digital conversion circuit 1 includes a charging circuit 2 having a capacitor C1 that stores a charge corresponding to the input current Iin. A switch SW1 that includes a discharge circuit 6 that discharges electric charge, includes a comparison circuit 3 that compares the output voltage vsig of the charging circuit 2 and a reference voltage vref, and opens and closes between the output of the voltage source V1 and the output of the charging circuit 2 Is provided. The analog-digital conversion circuit 1 also includes a switch control circuit 7 that outputs a switch control signal for controlling the opening / closing of the switch SW1 to the switch SW1, and the digital signal corresponding to the number of discharges from the comparison signal comp output from the comparison circuit 3 is provided. A control circuit 4 that outputs a value is provided, and a PWM control circuit 5 that controls the discharge charge amount of the discharge circuit 6 by PWM (pulse width modulation).

  By using the analog-to-digital conversion circuit 1, analog-to-digital conversion with a wide dynamic range and high resolution provided in the integral type analog-to-digital conversion circuit is possible.

  At the start of the operation of the analog-digital conversion circuit 1, the switch SW1 is closed by a switch control signal from the switch control circuit 7. For this reason, the output voltage vsig of the charging circuit 2 which is an integration circuit is charged to the reference voltage vref. During the charging period (data conversion time) t_conv, the switch SW1 is opened by a switch control signal from the switch control circuit 7, whereby the charge is charged in the capacitor C1 by the input current Iin, and analog-digital conversion is performed. The detailed operation of the analog-digital conversion circuit 1 is shown below.

  First, the discharge circuit 6 discharges a constant charge Iref * t_clk * α (precharge operation). Here, Iref is a reference current output from the current source I1, and t_clk is a cycle of the clock signal (clock signal) clk.

  Thereafter, the charging circuit 2 (integrator), which is an integration circuit, is charged by the input current Iin, and when the output voltage vsig of the charging circuit 2 exceeds the reference voltage vref, the comparison signal comp output from the comparison circuit 3 becomes the Hi voltage. become.

  The comparison signal comp is delayed by the D flip-flop D-FF and becomes the charge signal charge. The charge signal charge is pulse width modulated by the PWM control circuit 5 to become a pulse width modulated signal pwm. The pulse width modulation signal pwm becomes Hi as many times as the charge signal charge is input.

  When the pulse width modulation signal pwm is input to the switch SW2 of the discharge circuit and the switch SW2 is closed, a constant charge (Iref * t_clk) is discharged in the discharge circuit 6. By counting the number of discharges for a predetermined time by the counter 8, a value corresponding to the input charge amount is digitally output (DOUT).

FIG. 2 is a waveform diagram showing the operation of the integral type analog-digital conversion circuit 1 according to the embodiment of the present invention. Since the total charge amount due to the input current Iin and the total discharge amount due to Iref * t_clk * α operate to be equal, the following equations (1) and (2) are established.
Total charge amount = Iin * t_conv (1)
Total discharge charge = Iref * (α * t_clk) * count (2)
From the total charge charge amount = the total discharge charge amount, the following expression (3) is established.
count = (Iin * t_conv) / (Iref * α * t_clk) (3)
In the equations (1) to (3), t_clk is the cycle of the clock signal clk, t_conv is the charging period (data conversion time), count is the value of counting the number of discharges (count number), Iref is the reference current value, and α is It is a duty ratio by the PWM control circuit 5, and the duty ratio α takes a value of 0-1.

  From equation (3), the minimum resolution of the analog-digital conversion circuit 1 is determined by (Iref * α * t_clk), and the amount of discharge charge by the discharge circuit 6 is adjusted by adjusting the duty ratio α by the PWM control circuit 5. Can be adjusted.

  Thereby, the minimum resolution of the integral type analog-digital conversion circuit 1 can be adjusted by the duty ratio α by the PWM control circuit 5 without reducing the reference current value Iref in the discharge circuit 6. Therefore, it is possible to provide an analog-digital conversion circuit capable of setting a minimum resolution smaller than that of the conventional one without impairing measurement accuracy.

  Therefore, the integration type analog-digital conversion circuit 1 can be applied to an illuminance sensor that can measure even lower illuminance and a proximity sensor that can be detected by a minute input signal.

Here, when the charging period t_conv = t_clk * 2 ^ n (n is a resolution) (4) is set to charge for the period of t_clk * 2 ^ n, the following expression (5) is derived from the expression (3). The
count = Iin / (Iref * α) * 2 ^ n (5)
For example, when the resolution is n = 16 bits, the count number count outputs a value corresponding to the input current Iin in the range of 0 to 65535.

  FIG. 3 is a circuit diagram of the PWM control circuit 15 according to the embodiment of the present invention. The PWM control circuit 15 can be used as the PWM control circuit 5 of FIG.

  The PWM control circuit 15 includes a delay circuit (delay circuit, first delay circuit) 16, EXOR (Exclusive OR circuit, first and second exclusive OR circuits) 17, 18, a D flip-flop 19, and a variable delay. A circuit 20 is included.

  In the PWM control circuit 15, the clock signal clk is input to the input of the delay circuit 16. A clock signal (delayed clock signal) clk_d is output from the output of the delay circuit 16 to the clock signal input of the D flip-flop 19.

  The charge signal charge is input to the first input of the EXOR circuit 17. The output of the EXOR circuit 17 is connected to the input D of the D flip-flop 19. The second input of the EXOR circuit 17 is connected to the output Q of the D flip-flop 19, the first input of the EXOR circuit 18, and the input of the variable delay circuit 20. An output signal q is output from the output Q of the D flip-flop 19.

  The delayed output signal q_delay is output from the output of the variable delay circuit 20 to the second input of the EXOR circuit 18. Then, a pulse width modulation signal pwm is output from the output of the EXOR circuit 18.

  The PWM control circuit 15 having such a configuration counts the number of clock signals clk_d during the discharging period. Further, by adjusting the delay time in the delay output signal q_delay with the variable delay circuit 20, the duty ratio α can be adjusted by adjusting the pulse width of the pulse width modulation signal pwm.

  FIG. 4 is a waveform diagram showing the operation of the PWM control circuit 15 according to the embodiment of the present invention. In the discharge period (charge signal charge is Hi), the rising edge of the clock signal clk_d is detected and set as the output signal q. The exclusive OR of the delayed output signal q_delay obtained by delaying the output signal q by the variable delay circuit 20 and the output signal q is obtained by the EXOR circuit 18 to obtain the pulse width modulation signal pwm. The duty ratio α in the PWM control circuit 15 (PWM control circuit 5) can be adjusted by adjusting (increasing or decreasing) the time (delay amount) of delaying the output signal q in the variable delay circuit 20.

  FIG. 5 is a circuit diagram of the PWM control circuit 25 according to the embodiment of the present invention. The PWM control circuit 25 can be used as the PWM control circuit 5 of FIG.

  The PWM control circuit 25 in FIG. 5 adds a MOS transistor 26, a comparator 27, a variable current source 28, a variable capacitor 29, and a variable voltage source 30 to the PWM control circuit 15 in FIG. (Second delay circuit) This is a circuit replaced with 20 '. In the PWM control circuit 25, the MOS transistor 26, the comparator 27, the variable current source 28, the variable capacitor 29, and the variable voltage source 30 constitute a ramp circuit 40.

  In the PWM control circuit 25, the clock signal clk is input to the input of the delay circuit 16. The clock signal clk_d is output from the output of the delay circuit 16 to the clock signal input of the D flip-flop 19.

  The charge signal charge is input to the first input of the EXOR circuit 17. The output of the EXOR circuit 17 is connected to the input D of the D flip-flop 19. The second input of the EXOR circuit 17 is connected to the output Q of the D flip-flop 19, the first input of the EXOR circuit 18, and the input of the delay circuit 20 ′. An output signal q is output from the output Q of the D flip-flop 19.

  The delayed output signal q_delay is output from the output of the delay circuit 20 ′ to the second input of the EXOR circuit 18. A trigger signal trig is output from the output of the EXOR circuit 18 to the gate of the MOS transistor 26.

  A power supply voltage Vdd is applied to the input of the variable current source 28. The output of the variable current source 28 is connected to the source of the MOS transistor 26, one end of the variable capacitor 29, and the inverting input terminal (−) of the comparator 27. The ramp signal ramp is input to the inverting input terminal (−) of the comparator 27.

  The drain of the MOS transistor 26, the other end of the variable capacitor 29, and the input of the variable voltage source 30 are electrically grounded. The output of the variable voltage source 30 is connected to the non-inverting input terminal (+) of the comparator 27. Then, a pulse width modulation signal pwm is output from the output of the comparator 27.

  The PWM control circuit 25 counts the number of clock signals clk_d during the discharge period, generates a trigger signal trig that is a pulse signal, and adjusts the pulse width of the pulse width modulation signal pwm by the ramp circuit 40 to adjust the duty ratio α. it can.

  FIG. 6 is a waveform diagram showing the operation of the PWM control circuit 25 according to the embodiment of the present invention. During the discharge period (charge signal charge is Hi), the rising edge of the clock signal clk_d is detected and set as the output signal q. The exclusive OR of the delayed output signal q_delay obtained by delaying the output signal q by the delay circuit 20 ′ and the output signal q is obtained by the EXOR circuit 18, whereby the trigger signal trig is obtained. By using the trigger signal trig as a trigger, the ramp signal ramp is generated, and the ramp signal ramp and the voltage value V2 of the variable voltage source 30 are compared by the comparator 27, whereby the pulse width modulation signal pwm is obtained.

The pulse width t_pwm of the pulse width modulation signal pwm is obtained by the following equation (6). Here, C2 is a capacitance value of the variable capacitor 29, V2 is a voltage value of the variable voltage source 30, and I2 is a current value of the variable current source 28.
t_pwm = C2 * V2 / I2 (6)
It becomes.

  The duty ratio α in the PWM control circuit 25 (PWM control circuit 5) can be adjusted by adjusting (increasing or decreasing) the current value I2 in the PWM control circuit 25. Further, the duty ratio α in the PWM control circuit 25 (PWM control circuit 5) can be adjusted by adjusting (increasing or decreasing) the capacitance value C2 in the PWM control circuit 25. Furthermore, the duty ratio α in the PWM control circuit 25 (PWM control circuit 5) can be adjusted by adjusting (increasing or decreasing) the voltage value V2 in the PWM control circuit 25.

  In the integration type analog-to-digital conversion circuit 1 of FIG. 1, analog-to-digital conversion with a wide dynamic range and high resolution is possible by inputting the current of a photodiode that receives light from outside and converts it into current. Thus, an illuminance sensor capable of measuring even lower illuminance than before can be configured.

  Further, in the integration type analog-to-digital conversion circuit 1 of FIG. 1, a light emitting diode (LED) that emits light for detecting a detection object by inputting a current of a photodiode that receives light from the outside and converts it into a current. And an LED driving circuit (light emitting diode driving circuit) for driving the light emitting diode. Thereby, analog-digital conversion with a wide dynamic range and high resolution is possible, and a proximity sensor that can detect a detected object with a minute input signal can be configured.

  FIG. 7A is a block diagram of the mobile phone 31 according to the embodiment of the present invention. The mobile phone 31 includes a liquid crystal panel 32 that displays a screen, a backlight 33 that illuminates the liquid crystal panel 32, a backlight control unit 34 that controls the luminance of the backlight 33, and an illuminance sensor 35 (or proximity sensor 35). The luminance of the backlight 33 is controlled based on the output signal of the analog-digital conversion circuit 1 included in the illuminance sensor 35 (or the proximity sensor 35).

  As described above, the analog-digital conversion circuit 1 can be applied to the control of the backlight 33 of the liquid crystal panel 32 included in the mobile phone 31.

  FIG. 7B is a block diagram of a digital still camera (digital camera) 41 according to the embodiment of the present invention. The digital still camera 41 includes a liquid crystal panel 42 that displays a screen, a backlight 43 that illuminates the liquid crystal panel 42, a backlight control unit 44 that controls the luminance of the backlight 43, and an illuminance sensor 45 (or a proximity sensor 45). The luminance of the backlight 43 is controlled based on the output signal of the analog-digital conversion circuit 1 included in the illuminance sensor 45 (or the proximity sensor 45).

  As described above, the analog-digital conversion circuit 1 can be applied to the control of the backlight 43 of the liquid crystal panel 42 included in the digital still camera 41.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The analog-digital conversion circuit of the present invention can be suitably used for an illuminance sensor, a proximity sensor, a mobile phone, and a digital camera because a minimum resolution smaller than the conventional resolution can be set without impairing measurement accuracy.

DESCRIPTION OF SYMBOLS 1 Analog-digital conversion circuit 2 Charging circuit 3 Comparison circuit 4 Control circuit 5,15,25 PWM control circuit (pulse width modulation control circuit)
6 Discharge circuit 7 Switch control circuit 8 Counter 16 Delay circuit (delay circuit, first delay circuit)
17, 18 EXOR circuit (first and second exclusive OR circuits)
19, D-FF D flip-flop 20 variable delay circuit 20 'delay circuit (second delay circuit)
26 MOS transistor 27, CMP1 comparator 28 variable current source 29 variable capacitor 30 variable voltage source 31 mobile phone 32, 42 liquid crystal panel 33, 43 backlight 34, 44 backlight control unit 35, 45 illuminance sensor 40 lamp circuit 41 digital still camera (Digital camera)
AMP1 Differential amplifier C, C1, C2 Capacitance Iin Input current Iref Reference current value SW1, SW2 Switch V1 Voltage source V2 Voltage value Vdd Power supply voltage charge Charge signal clk Clock signal (clock signal)
clk_d clock signal (delayed clock signal)
comp Comparison signal count Count n Resolution pwm Pulse width modulation signal q Output signal q_delay Delayed output signal ramp Ramp signal t Pulse width t_conv Charging period trig Trigger signal vref Reference voltage vsig Output voltage

Claims (9)

An integration type analog-digital conversion circuit that digitally converts and outputs the amount of input current,
A charging circuit having a capacity for storing charges according to the input current;
A discharge circuit for discharging the charge stored in the capacitor;
A comparison circuit for comparing the output voltage of the charging circuit and a reference voltage output from the voltage source;
A switch for opening and closing between the output of the voltage source and the output of the charging circuit;
A switch control circuit for outputting a switch control signal for controlling opening and closing of the switch to the switch;
A control circuit that outputs a digital value corresponding to the number of discharges from the comparison signal output from the comparison circuit;
An analog-digital conversion circuit comprising: a pulse width modulation control circuit for performing pulse width modulation control on a discharge charge amount of the discharge circuit. The pulse width modulation control circuit includes a delay circuit, first and second exclusive OR circuits, a D flip-flop, and a variable delay circuit,
A clock signal is input to the input of the delay circuit,
A delayed clock signal is output from the output of the delay circuit to the clock signal input of the D flip-flop,
A charge signal is input to the first input of the first exclusive OR circuit,
The output of the first exclusive OR circuit is connected to the input of the D flip-flop,
The second input of the first exclusive OR circuit is connected to the output of the D flip-flop, the first input of the second exclusive OR circuit, and the input of the variable delay circuit. ,
An output signal is output from the output of the D flip-flop,
A delayed output signal is output from the output of the variable delay circuit to the second input of the second exclusive OR circuit;
2. The analog-digital conversion circuit according to claim 1, wherein a pulse width modulation signal is output from the output of the second exclusive OR circuit. The pulse width modulation control circuit includes a first delay circuit, first and second exclusive OR circuits, a D flip-flop, a second delay circuit, a MOS transistor, a comparator, and a variable current source. And a variable capacitor and a variable voltage source,
The MOS transistor, the comparator, the variable current source, the variable capacitor, and the variable voltage source constitute a ramp circuit,
A clock signal is input to the input of the first delay circuit;
A delayed clock signal is output from the output of the delay circuit to the clock signal input of the D flip-flop,
A charge signal is input to the first input of the first exclusive OR circuit,
The output of the first exclusive OR circuit is connected to the input of the D flip-flop,
The second input of the first exclusive OR circuit is connected to the output of the D flip-flop, the first input of the second exclusive OR circuit, and the input of the second delay circuit. And
An output signal is output from the output of the D flip-flop,
A delayed output signal is output from the output of the second delay circuit to the second input of the second exclusive OR circuit;
A trigger signal is output from the output of the second exclusive OR circuit to the gate of the MOS transistor,
A power supply voltage is applied to the input of the variable current source,
The output of the variable current source is connected to the source of the MOS transistor, one end of the variable capacitor, and the inverting input terminal of the comparator,
A ramp signal is input to the inverting input terminal of the comparator,
The drain of the MOS transistor, the other end of the variable capacitor, and the input of the variable voltage source are electrically grounded,
The output of the variable voltage source is connected to the non-inverting input terminal of the comparator,
2. The analog-digital conversion circuit according to claim 1, wherein a pulse width modulation signal is output from the output of the comparator.   3. The analog-digital conversion circuit according to claim 2, wherein a time for delaying the output signal in the variable delay circuit is increased or decreased.   4. The analog-digital conversion circuit according to claim 3, wherein the current value of the variable current source, the capacitance value of the variable capacitor, or the voltage value of the variable voltage source is increased or decreased. A photodiode that receives light from the outside and converts it into a current;
An illuminance sensor comprising: the analog-digital conversion circuit according to claim 1, to which a current output from the photodiode is input. A light emitting diode that emits light to detect the detected object;
A light emitting diode driving circuit for driving the light emitting diode;
A photodiode that receives light from the outside and converts it into a current;
A proximity sensor comprising: the analog-digital conversion circuit according to claim 1, to which a current output from the photodiode is input. A liquid crystal panel that displays a screen;
A backlight for illuminating the liquid crystal panel;
A backlight control unit for controlling the luminance of the backlight;
The illuminance sensor according to claim 6 or the proximity sensor according to claim 7,
The mobile phone according to claim 1, wherein the backlight control unit controls the luminance of the backlight based on an output signal of the analog-digital conversion circuit. A liquid crystal panel that displays a screen;
A backlight for illuminating the liquid crystal panel;
A backlight control unit for controlling the luminance of the backlight;
The illuminance sensor according to claim 6 or the proximity sensor according to claim 7,
The digital camera according to claim 1, wherein the backlight control unit controls the luminance of the backlight based on an output signal of the analog-digital conversion circuit.

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