JP2000354074A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a receiver which restores binary signals by performing envelope detection on received signals and comparing the detected signals with a reference voltage to accurately restore the binary signals, even if the communication distance between the receiver and a transmitter changes. SOLUTION: This receiver is a portable receiver which performs envelop detection on signals received from a receiving section 10 by means of an envelope detection circuit 20 and restores binary signals (serial data), by comparing the detected signals with a reference voltage Vth by means of a comparator 40, after the detected signals are amplified by means of an amplifier circuit 30 and is provided with a CR filter 50 on the received-signal inputting path from the detection circuit 20 to the amplifier circuit 30. Consequently, an input signals Vin to the comparator 40 is made to have the center of its amplitude at a GND by the operation of the CR filter 50, even if the amplitude of a detection signal outputted from the detection circuit 20 varies as the communication distance between an external device and the receiver varies. Thus, the receiver can surely restore the binary signals by comparing the detected signals with the reference voltage Vth of several tens of mV which is slightly higher than the GND potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus for receiving a radio wave amplitude-modulated by a binary signal and restoring the binary signal from the received signal.

[0002]

2. Description of the Related Art Conventionally, amplitude modulation (specifically, amplitude displacement modulation; AS) is performed using a binary signal which is serial digital data.
K) As a demodulation method for demodulating a binary signal from the modulated wave, an envelope detection method and a synchronous detection method are known.

[0003] Among them, the modulated wave synchronous detection system recovers a binary signal by reproducing a carrier wave having the same phase as the modulated wave and multiplying the reproduced wave by the modulated wave. Although a binary signal can be accurately restored, a circuit for reproducing a carrier wave, a circuit for multiplication, and the like are required, which complicates the device configuration.

On the other hand, in the envelope detection method, the modulated signal is subjected to envelope detection, and a binary signal is restored from a change in amplitude of the detected signal, so that the device configuration is simplified. Therefore, when a receiving device that receives and demodulates a modulated wave that has been amplitude-modulated by a binary signal is incorporated in a portable electronic device that requires miniaturization and power saving, the demodulation method of the receiving device is used. Should be an envelope detection method.

[0005]

By the way, the conventional receiving apparatus adopting the envelope detection method usually converts a modulated wave from a resonance circuit of an antenna coil Lo and a capacitor Co, as shown in FIG. The received signal is received by the receiving unit 10, and the received signal is subjected to envelope detection by the envelope detection circuit 20 and then further amplified by the amplification circuit 30, and the detected signal after the detection and amplification is compared with the reference voltage. Circuit (comparator) 40
Are compared to generate a binary signal. Usually, in order to increase the receiving sensitivity of the radio wave received by the receiving unit 10, the antenna coil Lo and the capacitor Co are selected so that Q (resonance of resonance) of the receiving unit 10 becomes a large value. You.

However, when the Q of the receiving unit 10 is set to a large value, there is a problem that the signal waveform output from the receiving unit 10 to the envelope detection circuit 20 is distorted.
When a binary signal is generated using such a blunt signal waveform, when the distance (communication distance) between the transmitter and the transmitter changes, the binary signal may not be able to be accurately restored.

That is, as shown in FIG. 6, in the case of short-distance communication in which the communication distance is short, the signal level of the reception signal output from the reception unit 10 (in other words, the amplitude of the modulated wave) increases. The signal level of the input signal Vin to the comparator 40 after detection and amplification also increases. On the other hand, in the case of long-distance communication where the communication distance is long, the signal level of the received signal output from the receiving unit 10 (in other words, the amplitude of the modulated wave) becomes small, and thus the comparator after detection and amplification is used. The signal level of the input signal Vin to 40 becomes small. For this reason, conventionally, a binary signal can be generated from a change in the amplitude of the input signal Vin even during long-distance communication in which the amplitude of the input signal Vin is small (in other words, to increase the reception sensitivity of the modulated wave). The reference voltage Vref used for comparison with the input signal Vin on the comparator 40 side is connected to ground (GND).
A low voltage near the potential is set.

On the other hand, as shown in FIG. 5, an envelope detection circuit 20 includes a detection Schottky diode (hereinafter simply referred to as a diode) D1 for half-wave rectification of a received signal, and detection (half) by the diode D1. And a resistor R1 connected in parallel to the capacitor C1. The capacitor C1 is charged with a half-wave rectified reception signal by the diode D1. By discharging, a signal corresponding to the envelope of the modulated wave is output. As described above, when Q of the receiving unit 10 is set to a large value, the signal waveform output from the receiving unit 10 to the envelope detection circuit 20 becomes dull, so that the input signal Vin to the comparator 40 is As shown in FIG. 6, the amplitude of the received signal (modulated wave) output from the receiving unit 10 changes gradually in accordance with the amplitude change.

Therefore, the output from the comparator 40 (2
The value signal Vout is a signal received by the receiving unit 1 during long-distance communication where the reference voltage Vth is substantially the same level as the amplitude center of the input signal Vin.
0 is substantially the same as the pulse width P0 of the received modulated wave, but at the time of short-range communication in which the reference voltage Vth is lower than the amplitude center of the input signal Vin, the pulse width P0 of the received modulated wave is smaller. The pulse width P1 is also large, and the binary signal used for generation of the modulated wave cannot be accurately restored on the transmission device side, and desired digital data may not be obtained.

For this reason, the receiving device of the envelope detection system is
When incorporated into a portable electronic device, depending on the location of the person carrying the electronic device, normal data communication between the transmitting device on the base station side and the receiving device on the electronic device may not be possible. Problems arise.

The amplifier circuit 30 shown in FIG. 5 is a differential amplifier circuit composed of an operational amplifier, and includes a resistor R3 provided between an inverting input terminal (-) and an output terminal, and an inverting input terminal (-). ) And the ground, the detection signal output from the envelope detection circuit 20 is amplified at a predetermined amplification factor (R3 / R4) determined by the resistance value of the resistor R4. In addition, the comparator 40 receives the input signal Vin and the reference voltage Vth
And outputs a high-level signal determined by the power supply voltage Vcc when the input signal Vin is higher than the reference voltage Vth. In FIG. 5, the variable resistor V
The reference voltage Vth is set by dividing the power supply voltage Vcc using R1.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made by receiving an externally transmitted radio wave, performing envelope detection, and comparing a received signal after the envelope detection with a reference voltage. An object of the present invention is to provide a receiving apparatus for restoring a value signal (digital data) so that a binary signal can always be accurately restored even when a communication distance with a transmitting apparatus changes.

[0013]

According to a first aspect of the present invention, there is provided a receiving apparatus for receiving a radio wave transmitted from an external device, and a detecting means for receiving the received signal. And the output means restores the binary signal by comparing the magnitude of the received signal after the envelope detection with the reference voltage. Then, in the present invention, the signal processing means provided on the input path of the reception signal from the detection means to the output means shifts the reception signal so that the amplitude center of the reception signal becomes the ground potential of the device.

Therefore, according to the present invention, even if the amplitude of a received signal (detected signal) after envelope detection changes according to a change in the communication distance between the device and an external device, the output means can be used. , A reception signal whose ground potential is near the center of the amplitude is input. Therefore, by comparing the received signal with the reference voltage slightly higher than the ground potential in the output means, the binary signal can always be accurately restored.

Here, as the signal processing means, for example,
Detects the amplitude of the received signal (detected signal) after envelope detection,
From the detected amplitude, a shift amount for setting the center of the amplitude to the ground potential is obtained, and the detection signal is shifted by the shift amount. Although a shift circuit or the like may be used, such a circuit configuration complicates the device configuration.

Therefore, when actually configuring the receiving apparatus of the present invention, the signal processing means may be configured by a CR high-pass filter. That is, if a CR high-pass filter is used as the signal processing means, the DC component included in the signal after the envelope detection is cut off, and the output means receives the signal having the ground potential near the center of the amplitude of the signal after the envelope detection. A signal can be input.

Therefore, if the signal processing means is constituted by a CR high-pass filter, not only the same effect as the device according to the first aspect can be obtained, but also the signal processing means can be simplified by the capacitor C and the resistor R. This can prevent the device configuration from becoming complicated.

When a CR high-pass filter is used as the signal processing means, if the cut-off frequency of the CR high-pass filter is too high, the signal waveform after envelope detection is distorted. As described above, it is desirable to set a value at which a DC component included in the envelope-detected signal is cut to such an extent that the waveform of the envelope-detected signal is not distorted.

On the other hand, the output means is composed of an amplifier circuit and a comparison circuit, as in the conventional device shown in FIG. 5, and the reference voltage is set by dividing the power supply voltage with a variable resistor. You may do so. However, when the output unit is configured in the same manner as the conventional device, there is a problem that the adjustment operation of the reference voltage using the variable resistor is troublesome.

In other words, the reference voltage is for restoring a binary signal from the received signal after the envelope detection and signal processing, but the received signal is amplified by an amplifier circuit as in the prior art. In such a case, the detection signal input to the comparison circuit is affected by the offset of the amplification circuit and the like, and the signal level becomes different for each amplification circuit. For this reason, in the related art, in order to accurately restore a binary signal, a reference voltage is set using a variable resistor so that the reference voltage can be finely adjusted using the variable resistor. Also, in the present invention, if the output means is configured in the same manner as the conventional device, the reference voltage must be set using a variable resistor, and the adjustment work becomes troublesome.

Therefore, in order to eliminate the need for such adjustment work, the output means may be configured as described in claim 4. That is, in the receiving apparatus according to the fourth aspect, the output means amplifies the received signal by the amplifier circuit, and compares the amplified received signal with the reference voltage by the comparison circuit so as to convert the binary signal. Although it is configured to restore, a coupling capacitor for blocking a DC signal component is provided on an input path of a reception signal from the amplifier circuit to the comparison circuit, and the amplification circuit and the comparison circuit are AC-coupled. Then, by dividing the DC power supply voltage by the voltage dividing circuit, the first DC voltage and the second DC voltage higher than the first DC voltage are generated, and the first DC voltage is supplied to the input terminal of the received signal on the comparison circuit side. A DC voltage is applied, and the second DC voltage is input to a comparison circuit as a reference voltage.

For this reason, a signal obtained by superimposing a reception signal that has passed through a signal processing means such as a CR high-pass filter on the first DC voltage is input to the input terminal of the reception signal of the comparison circuit. The signal is compared in magnitude with a second DC voltage that is higher by a predetermined voltage than the first DC voltage. That is, in the comparison circuit, the received signal always becomes the first signal.
It is determined whether the voltage is higher than a certain level determined by the voltage difference between the DC voltage and the second DC voltage.

Therefore, according to the receiver of the fourth aspect, in the comparison circuit, the binary signal can be accurately restored without being affected by the offset of the amplifier circuit. Therefore, unlike the related art, there is no need to adjust the reference voltage according to the characteristics of the amplifier circuit, and the manufacturing process of the receiving device can be simplified.

According to the receiving apparatus of the present invention (claims 1 to 4), communication between the receiving apparatus and an external apparatus transmitting a transmission radio wave generated by amplitude-modulating a carrier with a binary signal is performed. Even if the distance changes, the binary signal can be accurately restored without being affected by the change in the distance. Therefore, the binary signal can be used by being incorporated in a portable electronic device. If configured as a portable receiving device,
The effect can be exhibited more effectively.

That is, since the portable electronic device is carried by the user, the distance between the portable electronic device and the external device as the communication partner changes, and the reception signal level at the receiving device also changes. According to the receiving apparatus of the present invention, a binary signal can be accurately restored without being affected by such a change in distance. Therefore, if the receiving apparatus is configured as a portable receiving apparatus, the effect can be exhibited effectively. You can do it.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an entire configuration of a keyless entry system for a vehicle according to an embodiment to which the present invention is applied.

The keyless entry system of the present embodiment
When the driver carrying the key unit 4 approaches the car 2, the door is automatically unlocked (unlocked).
Conversely, when the driver carrying the key unit 4 leaves the vehicle 2, the door is automatically locked (locked).

Then, in order to automatically perform the door locking and unlocking, the vehicle 2 side modulates a carrier having a predetermined frequency (134 kHz in this embodiment) with a predetermined calling code (binary signal) by amplitude modulation (binary signal). A transmitting device 2a for transmitting an ASK-modulated calling signal is provided. On the key unit 4 side, a receiving device 4a for receiving a calling signal from the transmitting device 2a and restoring a calling code, and a receiving device 4a. It is determined whether or not the restored calling code is from the specific vehicle 2 corresponding to the key unit 4. If the calling code is from the specific vehicle 2, a predetermined response code is determined. A code generator 4b for generating a code and a transmitter 4c for transmitting a response signal obtained by modulating a carrier with a response code generated by the code generator 4b are provided.

The transmission device 4c is provided on the side of the automobile 2.
In order to control the locking / unlocking of the door according to the response signal from the receiving device 2b, a receiving device 2b for receiving a response signal from the transmitting device 4c and restoring a response code, and a response restored by the receiving device 2b When the driver code is from the corresponding key unit 4, the driver carrying the key unit 4 approaches the vehicle 2 based on a change in the signal level of the response signal or the like, or the driver There is provided a door lock control device 2c which detects the separation and drives a door lock actuator (not shown) in accordance with the detection result to control locking and unlocking of the door.

According to the keyless entry system of the present embodiment configured as described above, the door is automatically unlocked only by the occupant such as the driver carrying the key unit 4 approaching the car. Since the door is automatically locked just by the driver or the like carrying the unit 4 moving away from the car, the door can be locked / unlocked by operating a switch provided on the key unit. Usability can be improved as compared with a conventional keyless entry system.

Since the key unit 4 is carried by an occupant such as a driver, it is required to be small and light. In particular, the key unit 4 is provided with a receiving device 4a which does not exist in the conventional keyless entry system. , It is necessary to reduce the size of the receiving device 4a.

Therefore, the receiver 4a of the envelope detection type described in the section of the prior art is employed, and even if the communication distance with the car 2 changes, the car 2
5 so that the calling code from the side can be accurately restored.
An improved version of the conventional receiver shown in FIG.

That is, as shown in FIG. 2, the receiving apparatus 4a of the present embodiment has a configuration similar to that of the conventional receiving apparatus shown in FIG. 5, and includes a receiving section 10 as receiving means and an envelope as detecting means. Line detection circuit 20, amplification circuit 30 as output means
And a comparison circuit (comparator) 40, and a CR high-pass filter (hereinafter simply referred to as a CR filter) 50 as a signal processing means on a signal path of the received signal from the envelope detection circuit 20 to the amplification circuit 30. Prepare. The receiving unit 10, the envelope detection circuit 20, the amplification circuit 3
Since 0 and the comparator 40 are exactly the same as those shown in FIG. 5, the description of the configuration is omitted.

In the receiving apparatus 4a according to the present embodiment, the communication distance between the vehicle 2 and the key unit 4 changes as shown in FIG. Even if the amplitude, that is, the amplitude of the received signal (detected signal) output from the envelope detection circuit 20 changes according to the communication distance, the comparator 40 outputs C
By the operation of the R filter 50, it is possible to input a reception signal (detection signal) Vin whose amplitude center is substantially at the ground potential.

That is, the CR filter 50 is connected between the capacitor C2 provided in series on the signal path of the received signal from the envelope detection circuit 20 to the amplifier circuit 30 and the capacitor C2 between the amplifier circuit 30 side and the ground. , And AC-couples the envelope detection circuit 20 and the amplification circuit 30. For this reason,
A DC signal included in the signal detected by the envelope detection by the envelope detection circuit 20 is cut into the amplification circuit 30 and, consequently, the comparator 40, and a detection signal having an amplitude center at a ground (GND) potential is input. be able to.

The cut-off frequency of the CR filter 50 is set to a value that can cut a DC component included in the envelope-detected signal so that the waveform of the envelope-detected signal is not distorted. In this embodiment, the cutoff frequency of the CR filter 50 is set to about 10 Hz by setting the capacitance of the capacitor C2 to 0.033 μF and the resistance of the resistor R2 to 470 kΩ. As a result, the received signal (detected signal) detected by the envelope detection by the envelope detection circuit 20 is input to the amplification circuit 30, and thus to the comparator 40, with the same waveform without causing waveform distortion. become.

Therefore, on the comparator 40 side, as shown in FIG. 3, the input signal Vin and the reference voltage Vth (several tens mV) set to a value slightly higher than the ground (GND) potential.
By comparing the magnitudes of the two values, the binary values of the pulse widths P1 and P2, which are substantially the same as the pulse width P0 of the modulated wave received by the receiving unit 10 at the time of short-range communication or long-range communication. The signal Vout can be restored, and the calling code from the car 2 can be accurately identified.

In the receiving apparatus 4a of this embodiment, the capacitance of the capacitor C1 and the resistance of the resistor R1 constituting the envelope detection circuit 20 are 100 pF and 1 MΩ, respectively. R3 and R4 that determine
Are 680 kΩ and 10 kΩ, respectively, and the power supply voltage Vcc is 3 V DC.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various embodiments can be adopted. For example, the receiving apparatus 4a shown in FIG. 2 is obtained by adding a CR filter 50 to the conventional receiving apparatus shown in FIG. 5, and the other configuration is completely the same as that shown in FIG. In the case, the amplification circuit 30
In order to be able to accurately restore the binary signal without being affected by the offset, it is necessary to adjust the resistance divided value of the variable resistor VR1 for setting the reference voltage Vth.

Therefore, in order to eliminate the need for such an adjustment operation, the receiving apparatus may be configured as shown in FIG. 4 by applying the invention described in claim 4. That is, the receiving apparatus shown in FIG. 4 is basically the same as the receiving apparatus of the above-described embodiment shown in FIG. 2, and the points different from those of the above-described embodiment are as follows.

A coupling capacitor Ca for blocking a DC signal component is provided on a path of a reception signal from the amplifier circuit 30 to the non-inverting input terminal (+) of the comparator 40. The power supply voltage Vcc is set to 3 instead of the variable resistor VR1.
Voltage is divided by a resistor series circuit composed of two resistors Rb, Rc, and Rd, and a voltage dividing point (a connection point between the resistor Rb and the resistor Rc) having a higher voltage value is selected from two voltage dividing points of the resistor series circuit. A point at which the DC voltage (second DC voltage) is applied to the inverting input terminal (−) of the comparator 40 as the reference voltage Vth.

The DC voltage (first DC voltage) at the other voltage dividing point (the connection point between the resistance Rc and the resistance Rd) where the voltage value becomes low, between the two voltage dividing points of the resistance series circuit, Through a non-inverting input terminal (+), which is a reception signal input terminal of the comparator 40, and a capacitor Cb for preventing voltage fluctuation between the voltage dividing point to which the resistor Ra is connected and the ground. Point provided.

When the receiving apparatus is configured as shown in FIG. 4, the reference voltage Vth is always higher than the DC voltage level of the reception signal input terminal of the comparator 40 by a constant voltage Vth.
The voltage becomes higher by th. The comparator 40 can determine whether or not the signal level of the received signal input via the coupling capacitor Ca is higher than the voltage Vtho. Therefore, according to the receiving apparatus shown in FIG. 4, it is possible to always accurately recover the binary signal without being affected by the offset of the amplifier circuit 30 and a temperature change of the offset.

On the other hand, in the above-described embodiment, the receiving apparatus used by being incorporated in the key unit 4 of the keyless entry system has been described as an example of the receiving apparatus to which the present invention is applied. The present invention is not limited to 4, and can be used by being incorporated in any electronic device. And, as described above, in particular, if it is incorporated in a portable electronic device such as the key unit 4,
The effect can be exhibited effectively.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a keyless entry system according to an embodiment.

FIG. 2 is an electric circuit diagram illustrating a configuration of a receiving device 4a according to the embodiment.

FIG. 3 is an explanatory diagram illustrating an operation of the receiving device 4a according to the embodiment.

FIG. 4 is an electric circuit diagram illustrating another configuration example of the receiving device 4a of the embodiment.

FIG. 5 is an electric circuit diagram illustrating a configuration of a conventional receiving device.

FIG. 6 is an explanatory diagram illustrating an operation of a conventional receiving device.

[Explanation of symbols]

4 key unit, 4a receiving device, 10 receiving unit, 2
0: envelope detection circuit, 30: amplification circuit, 40: comparator, 50: CR filter, VR1: variable resistor, Ca
... coupling capacitors, Ra, Rb, Rc, Rd ...
resistance.

Claims (5)

[Claims] 1. A receiving means for receiving a radio wave transmitted from an external device, a detecting means for performing envelope detection on a signal received from the receiving means, and a reception signal and a reference voltage after envelope detection by the detecting means. Output means for comparing the magnitudes and outputting a binary signal according to the comparison result, wherein the amplitude center of the received signal is on an input path of the received signal from the detection means to the output means. A receiving device comprising signal processing means for shifting the received signal so as to be at the ground potential of the device. 2. The receiving apparatus according to claim 1, wherein said signal processing means comprises a CR high-pass filter. 3. The cut-off frequency of the CR high-pass filter is set to a value that cuts a DC component included in the envelope-detected signal so that the waveform of the envelope-detected signal is not distorted. 3. The method according to claim 2, wherein
The receiving device according to the above. 4. An output circuit comprising: an amplification circuit for amplifying the reception signal; a comparison circuit for comparing a magnitude of the reception signal amplified by the amplification circuit with the reference voltage; A coupling capacitor provided in an input path of the received signal, for blocking a DC signal component output from the amplification circuit; and a first DC voltage and a second DC voltage higher than the first DC voltage by dividing a DC power supply voltage. A voltage dividing circuit that generates a DC voltage, applies a first DC voltage to an input terminal of the reception signal of the comparison circuit, and inputs the second DC voltage as the reference voltage to the comparison circuit. The receiving device according to claim 1, wherein: 5. The receiving device according to claim 1, wherein the receiving device is a portable device incorporated in a portable electronic device.