JPH06224855A - Light receiver for infrared pulse communication system - Google Patents

Abstract

PURPOSE:To prevent the pulse width of an output signal from being expanded by detecting the size of average direct currents supplied to a photodiode, and varying the resistance value of the load resistor of the photodiode according to the size. CONSTITUTION:The source of photocurrent flowing from a photodiode P.D is supplied from a power source +5V, and average direct currents Idc are supplied from the power source +5V. The size of the average direct currents Idc supplied from the power source +5V is detected by a current detecting resistor 1 as a detected voltage Vc. Then, the detected voltage Vc detected by the current detecting resistor 1 is impressed to a variable load resistor 2 as a control voltage. The resistance value of the variable load resistor 2 is controlled according to the level of the impressed detected voltage Vc. That is, the resistance value of the load resistor 2 is controlled so as to be decreased according as the detected voltage Vc is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared pulse communication system using infrared light such as a wireless device or a remote control device in which a device for transmitting infrared light or a device for receiving infrared light is movable. The present invention relates to a light receiving device that operates. Conventionally, as a wireless device and a remote control device, a device using radio waves, a device using ultrasonic waves, a device using infrared light, and the like are known.

Of these, wireless devices and remote control devices using radio waves are greatly affected by city noise, difficult to have directivity, and difficult to maintain confidentiality, as well as the Radio Law. However, it has the drawback that it is difficult to handle due to the regulations. Further, the wireless device and the remote control device using ultrasonic waves also have drawbacks such that the influence of city noise is great and the directivity is changed by wind.

For this reason, a general wireless device or remote control device is not easily affected by city noise, can have a predetermined directivity with a simple structure, and is inexpensive and easy to handle. The one using is exclusively used.

FIG. 9 shows a block diagram of a conventional general infrared remote control device. In FIG. 9, an infrared remote control device includes a transmitting device 200 for transmitting infrared light and a light receiving device 300 for receiving the transmitted infrared light.
Consists of. 101 is a control signal generator that generates a control signal for controlling the control circuit 110, 102 is a coding circuit that codes the control signal into a pulse signal, 103 is a modulator (MOD) that amplitude-modulates the pulse signal, and 104 is MOD1.
An oscillator (OSC) that generates carriers to be applied to
Reference numeral 105 denotes an LED that emits infrared light according to the modulation output, and includes the control signal generator 101, the coding circuit 102,
Infrared transmitter 20 with MOD 103 and OSC 104
0 is configured.

Next, 106 is a photodiode for receiving the infrared light emitted from the LED 105, and 107 is an amplifier (AM) for amplifying the output current of the photodiode 106.
P) and 108 are demodulation circuits (DEMOD) for demodulating the amplitude-modulated signal by envelope detection and performing waveform shaping.
Reference numeral 09 is a decoder for decoding a coded signal, 110 is a control circuit controlled by the control signal, 300 is a photodiode 106, AMP 107 and DEMOD 108,
The light receiving device includes a decoder 109 and a control circuit 110.

The infrared remote control device shown in FIG. 10 has a control signal when an operator operates a button or the like provided in the transmitting device 200 when the operator operates a television, a VTR or the like provided with the light receiving device 300. The generator 101 generates a control signal according to the operated button,
This control signal is made into a pulse of a predetermined code signal by the encoding circuit 102.

The coded pulse signal is the OSC 104
Amplitude modulation is performed by the MOD 103 by the carrier generated in 1. to obtain an amplitude-modulated pulse signal as shown in FIG. This pulse signal is applied to the LED 105 and LE
The D105 is driven by this pulse signal and sends out pulsed infrared light. The pulsed infrared light transmitted from the LED 105 is received by the photodiode 106 of the light receiving device 300.
The light is received by and a photocurrent corresponding to the amount of received light is induced in the photodiode 106 by the photoelectric effect.

The photocurrent induced in the photodiode is A
The signal is amplified by the MP 107, applied to the DEMOD 108, envelope-detected, demodulated and waveform-shaped. The demodulated signal whose waveform has been shaped is decoded by the decoder 109 and applied to the control circuit 110, and the control circuit 110 performs a desired operation such as television or VTR. In addition, O
The oscillation frequency of the SC 104 is a low frequency, and for example, the oscillation frequency is generally selected from the frequencies of 30 to 40 kHz.

An example of a wireless device using infrared rays will be described with reference to the block diagram of the wireless microphone shown in FIG. In FIG. 10, 201 is a microphone for converting a voice signal into an electric signal, 202 is an amplifier for amplifying the output of the microphone 201, 203 is a sampling and holding circuit for sampling and holding the amplifier output signal with a clock from a clock generator 207, 20
4 is a comparator for comparing the level of the hold output of the sampling and holding circuit 203 and the sawtooth wave generated by the sawtooth wave generator 208, 205 is a monostable multivibrator triggered by the edge of the comparator 204, and 206 is An LED driven by the pulse output from the monostable multivibrator 205 and transmitting infrared light, 207 is a clock generator that generates the sampling pulse of the sampling and holding circuit 203 and a trigger pulse of the sawtooth wave generator 208, and 208 is A sawtooth wave generator that generates a sawtooth wave in synchronization with a trigger pulse from the clock generator 207,
The microphone 201, amplifier 202, sampling and holding circuit 203, comparator 204, monostable multivibrator 205, LED 206, clock generator 20.
7. The sawtooth wave generator 208 constitutes the infrared light transmission unit 400, and the audio signal from the microphone 201 is pulse position modulated (PPM) and then transmitted as infrared light from the transmission unit 400. ing.

Next, in FIG. 10, 210 is an LED 20.
A photodiode that receives the infrared light transmitted from 6;
Reference numeral 211 is an amplifier that amplifies the photocurrent signal output from the photodiode 210, 212 is a waveform shaping circuit that shapes the output signal of the amplifier 211, and 213 is a waveform that is shaped into a sawtooth wave generated from a sawtooth wave generator 219. Circuit 212
A superimposing circuit for superimposing the output of
Clipper 215 cuts out the lower side of the output of
Hold circuit for holding the output of 14; 216, LPF for smoothing the output of hold circuit 215; and 217, LPF
A speaker for converting an output into an audio signal or the like, 218 is a clock generator for generating a trigger pulse of the sawtooth wave generator 219, and 219 is a sawtooth wave generator for generating a sawtooth wave by the trigger pulse from the clock generator 218. The photodiode 210, the amplifier 211, the waveform shaper 212, the superposition circuit 213, the clipper 214, the hold circuit 215, the LPF 216, the speaker 217, the clock generator 218, and the sawtooth wave generator 219 constitute the light receiving unit 500. PPM for demodulating a PPM-modulated signal
It has a demodulation unit.

FIG. 11 shows a waveform diagram of the PPM modulation operation of the transmitter 400 of the wireless microphone shown in FIG. 10, and FIG. 12 shows a PPM demodulation operation of the light receiver 500. The operation of the transmission unit 400 of the wireless microphone shown in FIG.
This will be described with reference to the operation waveform chart shown in FIG.

In the wireless microphone shown in FIG. 10, the signal converted into an electric signal by the microphone 201 is amplified by the amplifier 202 to be an analog signal as shown in FIG. 11a. This analog signal is applied to the clock generator 20 shown in FIG.
Sampling and holding by the clock from 7
The signal is a stepwise signal as indicated by SH in c.
The level of this signal SH is compared with the level of the sawtooth wave from the sawtooth wave generator 208, which is shown in FIG. Such a pulse width modulated pulse is output.

The positive trailing edge of the pulse width modulated pulse shown in FIG. 11d is generated at the time when the level of the signal SH and the level of the signal ST coincide with each other. By triggering the vibrator 205, FIG.
A narrow pulse as shown by e can be output from the monostable multivibrator 205. This Figure 1
The time position of the pulse shown in FIG.
Since it changes according to the level of H, the audio signal and the like shown in FIG. 11a has the PPM as shown in FIG. 11e.
It is a modulated pulse signal. The PPM-modulated pulse signal shown in FIG. 11e is applied to the LED 206, and the PPM-modulated pulsed infrared light is transmitted from the LED 206.

Next, the operation of the light receiving section 500 shown in FIG. 10 will be described with reference to the operation waveform diagram shown in FIG. PPM transmitted from the LED 206 of the transmission unit 400
The modulated pulsed infrared light is incident on the photodiode 210 of the light receiving unit 500, and the photodiode 210 outputs a photocurrent according to the amount of incident light by the photoelectric effect.
This photocurrent is amplified by the amplifier 211 and then shaped by the waveform shaping circuit 212 into a pulse having a narrow width as shown in FIG. 12a.

The shaped narrow pulse and sawtooth S generated by the sawtooth generator 219 shown in FIG. 12a.
T and T are superposed by the superposition circuit 213 to form a signal having a waveform in which the pulse shown in FIG. 12a is superimposed on the sawtooth wave ST as shown in FIG. 12b. The signal shown in FIG. 12b output from the superposition circuit 213 is clipped by the clipper 214 at the clip level shown by the alternate long and short dash line in FIG. 12b, and the level components below the clip level are cut out, and the signal is shown in FIG. 12c. The pulse signal is pulse amplitude-modulated as described above.

The pulse amplitude-modulated pulse signal output from the clipper is held in the hold circuit 215 by the amplitude of the pulse and is made into a stepwise signal as shown in FIG. 12d. The held staircase signal is LPF
At 216, a smooth signal as shown in FIG.

The clock generator 20 of the transmission unit 400
7 and the clock generator 218 of the light receiving section 500 are synchronized by a synchronizing means (not shown). Therefore, the sawtooth wave generated by the sawtooth wave generator 208 of the transmitting section 400 and the sawtooth wave of the receiving section 500 are synchronized. It is also synchronized with the sawtooth wave generated by the sawtooth wave generator 219.

[0018]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the remote control device and the wireless device as described above,
FIG. 4 shows an LED that transmits infrared light, a transmitter that drives the LED, a photodiode that receives infrared light, and a light receiver that drives the photodiode.

In FIG. 4, nine LEDs are connected in series, and when the FET T1 is turned on, the LED is 28V.
It is driven by the power source to emit infrared light. FETT
Reference numeral 1 is an output of the inverter N1 and is "ON" / "OFF" controlled. For example, a PPM pulse signal is applied to the inverter N1. Then, the LEDs will send out the PPM-modulated infrared light, but the LEDs will be driven by pulses, so-called dynamic driving, and therefore a driving current of about 6 times the rated current will be applied to these LEDs. The amount of infrared light to be supplied can be increased by the amount that can be supplied and the driving current can be increased.

Particularly, in the case of a PPM-modulated pulse, since the duty ratio of the pulse is small, the drive current can be made particularly large. Therefore, the infrared light emitted from the LED reaches far away. In this way, the infrared light sent from the LED is connected to the photodiode P.P. A photocurrent corresponding to the amount of incident light is incident on the photodiode P.D. The photocurrent flows to D and is supplied to the load resistance RL, and the voltage generated across the load resistance RL is output as an output voltage via the output terminal OUT. The capacitors C1, C2 and C3 are + 28V
Is connected to the power source for the purpose of stabilizing the power source of or the power source of + 5V.

By the way, the LED shown in FIG. As the distance R from the photodiode P. It can be easily understood that the amount of infrared light incident on D increases and the output voltage increases. However, the relationship between the distance R and the output voltage V0 output from the output terminal OUT, and +5 of time
V power source to photodiode P. Table 1 shows a table of the relationship between the average DC current Idc supplied to D and the distance R, and FIG. 5 shows a graph of this table 1.

[Table 1]

In the graph shown in FIG. 5, the horizontal axis represents the distance R [cm] between transmission and reception, and the vertical axis represents the output voltage V0.
[V] and average DC current Idc [mA]. As shown in this figure, in the case of the infrared pulse communication system as described above, the output voltage V increases as the distance R increases.
Both 0 and the average DC current Idc gradually decrease. By the way, it is considered that the output voltage V0 increases as the distance R decreases, and the transmission state is improved, but in reality, the waveform of the output voltage V0 is distorted. Waveforms in which this distortion occurs are shown in FIGS. In FIG. 6, when the distance R is 10 [cm], in FIG. 7, the distance R is 3 [cm].
8 shows the waveform of the output voltage V0 when the distance R is 1.5 [cm].

6 to 8, a rectangular waveform shown by a broken line is a pulse signal for driving an LED that emits infrared light, and this pulse signal has a pulse width of 0.3 μs, for example. The waveform shown by the solid line is the waveform of the output voltage V0. Referring to FIGS. 6 to 8, the distance R is 10 [cm].
The waveform of the output voltage V0 at this time is a triangular pulse whose rising and falling portions are delayed, but its pulse width is a little wider than the LED driving pulse. When the distance R is 3 [cm], the pulse has a trailing delay and the pulse width is about 10% wider than the pulse for driving the LED.
Further, when the distance becomes 1.5 [cm], the pulse becomes a pulse whose fall is extremely delayed, and its pulse width is expanded to a pulse having a width twice or more the pulse for driving the LED.

When the pulse width is extended in this way, the following problems occur. Although not shown in the light receiving section,
Usually, in order to remove noise, there is provided means for verifying the received light pulse width and removing noise except for pulses of a predetermined width, so that if the pulse width is expanded as shown in FIGS. 7 and 8. The signal with the expanded pulse width may be regarded as noise and may be removed, and it may not be possible to obtain a correct demodulated signal from the light receiving unit.

The reason why the pulse width is expanded as shown in FIGS. 7 to 8 is that the LED of the transmitter and the photodiode P. When the photodiode P. D
The amount of light incident on the photodiode P. It is considered that the phenomenon of the storage effect occurs in D, and the light reception pulse width is expanded due to the storage effect.

As the above-mentioned problem occurs when the light receiving pulse width is expanded, the result of repeated studies on means for preventing the light receiving pulse width from being expanded results in the photodiode P.
It has been confirmed by experiments that the phenomenon in which the pulse width of the output voltage is expanded is eliminated by reducing the resistance value of the load resistance of D. However, the photodiode P. D
Even if the load resistance of the photodiode P. Since the photocurrent induced in D does not increase, when the distance R is long, the output voltage V0 generated across the load resistance becomes small, which causes a problem that the light receiving sensitivity of the light receiving portion is lowered.

Therefore, according to the present invention, the LED of the transmitter and the photodiode P. An infrared pulse communication type light receiving device is provided in which the pulse width of the output voltage is not expanded even when D approaches, so that demodulation can be performed correctly and the light receiving sensitivity is not lowered. Has an aim.

[0028]

In order to achieve the above-mentioned object, the light receiving device of the present invention is such that, firstly, when the resistance value of the load resistance of the photodiode of the light receiving portion is reduced, the output signal output from the photodiode is reduced. Pulse width does not extend,
Secondly, it was made paying attention that the average DC current from the power source supplied to the photodiode increases as the distance R decreases. That is, the light receiving device of the present invention detects the magnitude of the average DC current supplied to the photodiode, and by varying the resistance value of the load resistance of the photodiode according to the magnitude of the detected average DC current, The pulse width of the output signal output from the photodiode is prevented from being expanded.

[0029]

Function: The magnitude of the average DC current supplied to the photodiode is detected, and the resistance value of the load resistance of the photodiode is changed according to the magnitude of the detected average DC current. That is, when the distance between the LED of the transmitting unit and the photodiode of the light receiving unit is large and the light receiving pulse width is not expanded, the load resistance value is increased, and conversely the distance is close, and the light receiving pulse width is expanded. In this case, the load resistance value is variably controlled to be small. Then, the pulse width of the output voltage is prevented from expanding without lowering the output voltage of the photodiode, and the transmitted signal is correctly demodulated without lowering the light receiving sensitivity.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an LED for transmitting infrared light, a transmitter for driving the LED, a photodiode for receiving infrared light according to the present invention, and a light receiver for driving the photodiode.
In FIG. 1, the same symbols as those in FIG. 4 indicate the same portions, and detailed description thereof will be omitted. In this figure, reference numeral 1 is a power supply +5 V to the photodiode P. Average DC current Id supplied to D
A current detecting resistor for detecting c, 2 is an output voltage V0
Is a variable load resistance for taking out.

The operation of the LED for emitting infrared light and the portion for driving the LED shown in FIG. 1 is the same as the operation of the LED for emitting infrared light and the portion for driving the LED shown in FIG. Although omitted, the nine LEDs connected in series emit PPM-modulated pulsed infrared light. The transmitted infrared light is transmitted to the photodiode P.I. D
The light is received by the photodiode P. Due to the photoelectric effect, a photocurrent corresponding to the amount of incident infrared light is induced in D and flows out. This photodiode P. The source of the photocurrent flowing out from D is supplied from the power source + 5V, and the average DC current Idc is supplied from the power source + 5V.

The magnitude of the average DC current Idc supplied from the power source + 5V is detected as the detection voltage Vc by the current detection resistor 1. Then, the detection voltage Vc detected by the current detection resistor 1 is applied to the variable load resistor 2 as a control voltage. The resistance value of the variable load resistor 2 is controlled as follows according to the magnitude of the applied detection voltage Vc. That is, the resistance value of the load resistance 2 is controlled so that the resistance value of the load resistance decreases as the detection voltage Vc increases.

According to experiments, the resistance value of the load resistor 2 is, for example, about 160 ohms when the distance R is 10 [cm], and the distance R is
If is set to about 60 ohms when is 3 [cm],
Since there is almost no phenomenon that the pulse width of the output voltage V0 extends, the resistance value of the load resistor 2 may be controlled by the detection voltage Vc using the above resistance value as a guide.

As an example of the load resistance 2, the load resistance 2 is F
An example of the ET is shown in FIG. In FIG. 2, the load resistor 2 is configured by using the drain-source of the FET, and the detection voltage Vc is applied as a control voltage to the gate of the FET, so that the drain-source of the FET is connected according to the control voltage Vc. By varying the resistance value, the resistance value of the load resistor 2 composed of the FET is controlled. Any resistance value may be selected as the resistance value of the average DC current detection resistance 1 as long as the resistance value is large enough to obtain an output from the load resistance 2.

Next, another embodiment of the variable load resistance 2 and another embodiment of the average DC current detection circuit associated therewith are shown in FIG. In FIG. 3, parts having the same symbols as those in FIG. 1 are the same parts, and detailed description thereof will be omitted. In this figure, R3 and R4 are cascaded average DC current detecting resistors, R5 is a safety resistor, TR1 and TR2 are transistors which are combined with the average DC current detecting resistors R3 and R4 to generate detection signals, respectively. TR3 and TR4 are switching transistors that are controlled to be "on" or "off" by a detection signal generated from the transistors TR1 and TR2, and RL1, RL2, and RL3 are connected in parallel and combined with the switching transistors TR3 and TR4 to form resistors. This is the load resistance whose value can be switched.

The load resistance is a switching transistor TR
3 and the switching transistor TR4 are "off", the resistance becomes RL1 and the switching transistor TR3
Is on and the switching transistor TR4 is off, the resistance value is the parallel resistance value of the resistors RL1 and RL2. When both the switching transistor TR3 and the switching transistor TR4 are on, the resistance RL1,
Since the parallel resistance value of the RL2 and the resistor RL3 is set, the resistance value of the load resistor is reduced each time the switching transistor TR3 and the switching transistor TR4 are turned on.

The resistance value of the resistor R3 is, for example, an LED and a photodiode P.I. The resistance value is such that the transistor TR1 is "on" when the distance R from D is 10 [cm]. That is, when the distance R is 10 [cm], the photodiode P. Average DC current Id from the power source supplied to D
c is about 0.18 [mA] from the graph of FIG. 5, and the transistor TR1 has a base-emitter voltage of about 0.
When it is 7 [V], it turns on, so that R3 = 0.7 [V] /0.18 [mA] 3.9 [kΩ], and the resistance value of the resistor R3 is 3.9 [kΩ]. Just select it.

The resistance value of the resistor R4 is, for example, the LED and the photodiode P.P. The resistance value is such that the transistor TR2 is turned “on” when the distance from D becomes 3 [cm]. That is, when the resistance value of the resistor R4 is calculated in the same manner as the case of the resistor R3, the average DC current Idc is 1 [mA] when the distance R is 3 [cm], and the switching transistor TR4 also has a base-emitter voltage. About 0.7
When it is [V], it is “ON”, and therefore R4 = 0.7 [V] ÷ 1 [mA] = 0.7 [kΩ], and 700 [Ω] may be selected as the resistance value of the resistor R4. The resistor R5 is a safety resistor that prevents an excessive current from flowing, and a resistance value of 680 [Ω] is selected, for example.

The resistance values of the resistors R3, R4 and R5 of the average DC current detecting resistor 2 are selected as such resistance values. Further, for example, the resistance RL1 is 680 [Ω] and the resistance R is R.
220 [Ω] as L2 and 100 as resistance RL3
When the resistance value of [Ω] is selected, the operation of the light receiving circuit shown in FIG. 3 is as follows.

An LED for transmitting infrared light and a photodiode P.P. for receiving the infrared light are provided. The distance R from D is 10 [c
5], the average DC current Idc supplied from the +5 [V] power supply does not exceed 0.18 [mA] as shown in FIG. TR2 is also “off”. Therefore, the switching transistor TR3 controlled by the transistor TR1 is “off”, and the switching transistor TR4 controlled by the transistor TR2 is also “off”.
Therefore, the photodiode P. The photocurrent induced in D is supplied only to the load resistance RL1,
The output voltage V0 is output from both ends of 1 via the output terminal OUT.

LED and Photodiode P. When D approaches and the distance R exceeds 3 [cm] but is within 10 [cm], the average DC current Idc supplied from the power source is as shown in FIG.
Also, as shown in Table 1, since it exceeds 0.18 [mA], the base-emitter voltage of the transistor TR1 exceeds 0.7 [V], and the transistor TR1 turns on, but the average DC Since the current Idc does not exceed 1 [mA], the base-emitter voltage of the transistor TR2 does not exceed 0.7 [V], and the transistor TR2 is still in the "off" state.

Then, the transistor T turned "on"
The collector current of R1 is the switching transistor TR3
The switching transistor TR3 is supplied to the base of the switching transistor TR3 and turns on, but the transistor TR2 remains “off”, so that the switching transistor TR4 still holds the state of “off”. When the switching transistor TR3 is turned "on", the collector and the emitter of the switching transistor TR3 become conductive, so that the resistance R
This means that L2 is connected in parallel with the resistor RL1, and the combined resistance value becomes the resistance value of the load resistance. This combined resistance value is about 160 [Ω].

Further, the LED and the photodiode P. D
And the distance R is within 3 [cm], the average DC current Idc supplied from the power source exceeds 1 [mA] as shown in FIG.
The base-emitter voltage of R2 exceeds 0.7 [V],
Following the transistor TR1, the transistor TR2 is also “turned on”. Then, the transistor TR turned on
The collector current of 2 is supplied to the base of the switching transistor TR4, and the switching transistor TR4 is also turned “on” following the switching transistor TR3.

When the switching transistor TR4 is turned "on", the collector and emitter of the switching transistor TR4 become conductive, and the resistor RL3 connected to the collector is also connected in parallel to the resistor RL1, so that the resistors RL1, RL2. The combined resistance value, which is the resistance value of the RL3 connected in parallel, becomes the resistance value of the load resistance. This combined resistance value is about 60 [Ω].

[Table 2]

The LED of the light receiving device shown in FIG. Table 2 shows the relationship between the distance R from D and the output voltage V0 and the resistance value of the switched load resistance RL. Referring to Table 2, the distance R is 10
Even if the distance is within [cm], the resistance value of the load resistance RL becomes smaller as the distance R becomes smaller, so that the output voltage V0 never exceeds 1 [V], and the pulse waveform of the output voltage V0 appearing at the output terminal OUT. The phenomenon in which is expanded is eliminated, and the demodulation circuit connected to the output terminal OUT can correctly perform PPM demodulation.

The average DC current detecting resistors R3 and R4
And the resistance value of the safety resistance R5 and the load resistances RL1 and RL
2 and RL3 have the same resistance value as the photodiode P.P. Characteristics and number of D, characteristics of transistors TR1 to TR4, and output terminal O
The value is determined in consideration of the characteristics of the circuit connected to the UT, and is not limited to the resistance value shown above.

Further, although the load resistance is changed in three steps in the light receiving device shown in FIG. 3, it may be changed in four steps or more. In this case, it goes without saying that the circuit for detecting the average DC current Idc may also be capable of detecting the average DC current Idc in four or more stages.

[0048]

Since the present invention is constituted as described above, even if the distance between the LED for transmitting infrared light and the photodiode for receiving the infrared light is short, the pulse output from the photodiode is generated. Is not expanded, so that the light receiving device can obtain a correct demodulated signal. Therefore, there is an effect that the dynamic range of the transmissible distance can be widened even when a large output infrared light is output in order to increase the distance between the transmission and the reception. Further, according to the light receiving device of the present invention, it is possible to achieve the above-described effects without reducing the light receiving sensitivity of the light receiving device.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a light receiving circuit of the present invention.

FIG. 2 is a diagram showing an example of a variable resistance of a light receiving circuit.

FIG. 3 is a diagram showing another embodiment of the light receiving circuit of the present invention.

FIG. 4 is a diagram showing a conventional light receiving circuit.

FIG. 5 is a diagram showing a graph of a relationship between distance and average DC current.

[Fig. 6]

FIG. 8 is a diagram showing a pulse waveform output from a photodiode.

FIG. 9 is a diagram showing a block diagram of a conventional remote control device.

FIG. 10 is a block diagram of a conventional wireless microphone.

FIG. 11 is an operation waveform diagram of a transmitter of a conventional wireless microphone.

FIG. 12 is an operation waveform diagram of a receiving unit of a conventional wireless microphone.

[Explanation of symbols]

 1 Resistance for Average DC Current Detection 2 Variable Load Resistance 101 Control Signal Generator 102 Coding Circuit 103 Modulator 104 Oscillator 105 LED 106 Photodiode 107 Amplifier 108 Demodulator 109 Decoder 110 Control Circuit 200 Transmitter 300 Photoreceiver 201 Microphone 202 amplifier 203 sampling and holding circuit 204 comparator 205 monostable multivibrator 206 LED 207 clock generation circuit 208 sawtooth wave generation circuit 210 photodiode 211 amplifier 212 waveform shaping circuit 213 superposition circuit 214 clipper 215 hold circuit 216 LPF 217 speaker 218 clock generation Circuit 219 Sawtooth wave generation circuit 400 Transmitter 500 Light receiver T1 FET TR1, TR2, TR3, TR4 Njisuta R1, R2, R5 resistors R3, R4 average DC current detection resistor RL, RL1, RL2, RL3 distance between the load resistor C1, C2, C3 Capacitor N1 inverter R LED and photodiode

Claims (4)

[Claims] 1. A photodiode for receiving a pulse-modulated pulse signal of infrared light, a detecting means for detecting an average DC current amount supplied to the photodiode, and an output of a signal received by the photodiode. An infrared pulse communication type light receiving device, characterized in that the resistance value of the load resistor is variably controlled according to the output of the detecting means. 2. The load resistor comprises a plurality of sub resistance circuits in which a resistance and a switching means are connected in series in parallel with the main resistance, and the switching means of the sub resistance circuit responds to the output of the detection means. 2. The pulse communication type light receiving device according to claim 1, wherein the light receiving device is controlled so as to be sequentially turned on. 3. The pulse according to claim 1 or 2, wherein the resistance value of the load resistance is controlled to gradually decrease as the magnitude of the average DC current detected by the detection means increases. Communication type light receiving device. 4. The infrared pulse communication type light-receiving device according to claim 1, wherein the pulse signal of the infrared light is pulse position modulated.