JPH02101832A - Light receiving unit - Google Patents

Abstract

PURPOSE:To reduce effect by an external light by juxtaposing a parallel resonance circuit in terms of AC in parallel with a photodiode, passing an output signal of the parallel resonance circuit through an amplifier circuit and extracting a demodulated signal with a demodulation circuit. CONSTITUTION:A photodiode 1 receives a light such as an infrared ray modulated and sent with a signal. A parallel resonance circuit 2 is connected in parallel with the photodiode 1 in terms of AC. A charge generated in the photodiode 1 flows through the parallel resonance circuit 2 and converted into a voltage. The impedance of the parallel resonance circuit 2 is high in the vicinity of a carrier frequency and low in other frequencies. Thus, the voltage due to the charge generated by an external light is very less. Thus, a signal is generated in the input of the amplifier circuit 3 only when a carrier is sent and the output signal of the amplifier circuit 3 is demodulated into the original signal by a demodulation circuit 4. Thus, the effect of an external light is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit configuration of a light receiving unit of a receiving device in a system that transmits and receives light such as infrared light.

[Summary of the Invention] The present invention provides a light receiving unit in which a parallel resonant circuit is provided in parallel with the photodiode in an alternating current manner, an output signal of the parallel resonant circuit is passed through an amplifier circuit, and then a demodulated signal is extracted in a demodulation circuit. This configuration greatly simplifies the circuit configuration and greatly reduces the influence of external light.

[Prior Art] FIG. 2 shows a circuit diagram of a conventional light receiving unit. Second
In the figure, 31 is a photodiode, 7 is a load resistor,
33 is an amplifier circuit, 8 is a parallel resonant circuit, 9 is a level shift cool limiter-1lO is a demodulation circuit, 11 is a waveform shaper, 1
2 is an automatic bias adjuster. The light incident on the photodiode 1 is converted into voltage and input to the amplifier circuit 3 where it is amplified. In addition to the target light, the incident light usually includes light from indoor lights and external light from sunlight, so when strong external light enters, the input signal bias of the amplifier circuit 33 may fluctuate significantly. The signal is clipped, so the input bias of the amplifier circuit 33 is fixed by changing the impedance of the automatic bias adjuster 12 connected in parallel to the load resistor 7 according to the output level of the amplifier circuit 33. The output signal of the 6-order amplifier circuit 33 is input to the parallel resonant circuit 8, and only the signal of the target light is extracted.6 Normally, the target light is a carrier with a frequency of about 38 kHz interrupted by signal data. Therefore, if the parallel resonant circuit 8 is made to resonate at about 38 Hz, the signal of the target light can be extracted. , performs amplitude limitation after amplification, and demodulates the circuit 10.
, the carrier is removed and the signal data is extracted. Further, the signal data was waveform-shaped by a waveform shaper 11 and outputted.

[Problems to be Solved by the Invention] However, in the prior art described above, since both the external light and the target light are amplified by the amplifier circuit 33, the automatic bias adjuster 12
is necessary. Furthermore, when strong external light enters, the load impedance of the photodiode 1 decreases and the signal of the target light also decreases, resulting in a decrease in sensitivity when strong external light enters. Furthermore, it is necessary to increase the amplification degree of the amplifier circuit 33, resulting in a problem that the overall circuit scale becomes large.

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and its purpose is to provide a light receiving unit that has a simplified circuit configuration and is less susceptible to external light.

Means for Solving 1 Problem] The light receiving unit of the present invention includes a photodiode, a parallel resonant circuit connected in parallel to the photodiode in an alternating current manner,
The present invention is characterized by comprising an amplifier circuit that receives the parallel resonant circuit signal output as an input and amplifies the signal, and a demodulation circuit that receives the amplifier circuit signal as an input and demodulates and outputs the original signal.

[Function] According to the above configuration of the present invention, first, among the charges generated in the photodiode by the incident light, a signal near the resonant frequency of the parallel resonant circuit, that is, a carrier signal component of the target light, is transferred to the parallel resonant circuit. A voltage is generated across the circuit, but
For external light such as sunlight, which can be considered as direct current, or indoor light flickering at the commercial power frequency, the impedance of the parallel resonant circuit is low and almost no voltage is generated. Therefore, the signal of only the target light is input manually to the amplifier circuit, so the automatic bias adjuster that was required in the past becomes unnecessary, and problems caused by strong external light entering are eliminated. Since the automatic bias adjuster is no longer necessary and the amplification degree of the amplifier circuit can be reduced, the overall circuit configuration can be simplified.

[Embodiment 1 FIG. 1 is a circuit configuration diagram in an embodiment of the present invention,
1 is a photodiode that generates a charge according to the amount of incident light; 2 is a parallel resonant circuit connected in parallel to the photodiode 1 in an alternating current manner; 3 is a parallel resonant circuit that receives the output signal of the parallel resonant circuit 2 and amplifies the signal. 4 is an amplifier circuit; 4 is a demodulation circuit that removes carriers, demodulates signal data, and outputs the demodulated signal data to output terminal 5; 6 is a capacitor between power supplies.

FIG. 3 is a waveform diagram illustrating the operation of the circuit configuration diagram of FIG. 1. 13 is a signal data waveform, and 14 is a transmission signal waveform in which the carrier is turned on and off according to the signal data. 15 is an input waveform of the amplifier circuit 3. The charge generated in the photodiode 1 flows through the parallel resonant circuit 2 and is converted into a voltage. A frequency-impedance characteristic diagram of the parallel resonant circuit is shown in FIG. 4. In FIG. 4, the horizontal axis represents frequency and the vertical axis represents impedance. According to Figure 4, the impedance of the parallel resonant circuit is high near the carrier frequency (38K Hz), and the impedance is low at other frequencies.Therefore, there is very little voltage generation due to charges generated by external light. Sunlight can almost be considered as direct current, and indoor lights such as fluorescent lights and incandescent lights are hardly affected by the commercial power supply frequency, which is 60Hz or 50Hz.Therefore, the input waveform 15 of the amplifier circuit in Figure 3 is As shown, a signal is generated only when a carrier is transmitted.

In FIG. 3, 16 is the output waveform of the amplifier circuit 3, and 17 is the output waveform of the demodulation circuit 4.

The amplifier circuit 3 is composed of active elements such as FETs and transistors, and passive elements such as resistors and capacitors, and amplifies the input signal and outputs it while limiting resonance. FIG. 5 shows a circuit diagram of the amplifier circuit configuration side.

In Fig. 5, 18 is an input terminal, 19 is an output terminal, 2
0 is a FET, 21.22 is an npn transistor, and 23 is a pnp transistor. Each resistance value is set to obtain an appropriate degree of amplification, and each capacitance value is set so as not to amplify low frequency noise, especially hum noise caused by commercial power supply.

Next, Fig. 6 shows a circuit diagram of the demodulation circuit configuration side. In Fig. 6, 24 is a c-MO3'J toggable mono multi-vibration break, 25 is an input terminal, 26 is an output terminal, 27 is a resistor, and 28 is a capacitor. The 0 time setting is 27 resistors and 28 capacitors.
To be determined. Carrier frequency 38KHz period 26
．． Set the time to 3us or more.

The retriggerable mono multi-by-break 26 means that when a pulse-like signal is input to the input terminal 25, at that moment the output terminal 26, which has been at a low level, becomes a high level.
After maintaining the high level for a certain period of time t determined by the resistor 27 and capacitor 28, it returns to the low level. If the next pulse-like signal is input within a certain period of time, the high level continues for a certain period of time, starting from the second signal. When the amplifier circuit output waveform 16 shown in the waveform diagram of FIG. 3 is input, the output terminal 26 maintains a high level while the carrier signal is output, and after the carrier signal stops, remains at a high level for a certain period of time t. A sustained movement that returns to a low level.

In this way, the demodulation circuit output waveform 1 in the waveform diagram in FIG.
7 is obtained.

[Effects of the Invention] As described above, according to the present invention, a parallel resonant circuit is provided in parallel with the photodiode in an alternating current manner, and only the signal of the target light is inputted to the amplifier circuit, and then the original signal is converted to the original signal by the demodulation circuit. Since the configuration is to demodulate and output, an automatic bias adjuster is unnecessary. Also.

There is no decrease in sensitivity even when strong external light is incident, and as a result, there is no need to increase the amplification degree of the amplifier circuit, and the size of one circuit is reduced.

As described above, the present invention has the effect of providing a light receiving unit that has a simplified overall circuit configuration and is less susceptible to external light.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the light receiving unit of the present invention. FIG. 2 is a circuit configuration diagram showing a conventional light receiving unit. FIG. 3 is a waveform diagram illustrating the operation of FIG. 1. FIG. 4 is a frequency-impedance characteristic diagram of a parallel resonant circuit. FIG. 5 is a circuit diagram of the amplifier circuit configuration side. FIG. 6 is a circuit diagram of the demodulation circuit configuration side. l. 2 ・3. 4 ・ 5 ・ 6 ・ 7 ・ 8 ・ 9 ・ l O・ l 1 ・ l 2 ・ l 3 ・ l 4 ・ 15 ・ 16 ・ l 7 ・ Photodiode parallel resonant circuit amplifier circuit demodulation circuit output terminal capacitor load resistance between power supply Parallel resonant circuit level shifter limiter Demodulation circuit Waveform shaper Automatic bias adjuster Signal data waveform Transmission signal Input of waveform amplification circuit Output waveform of the waveform amplification circuit Output waveform of the demodulation circuit 18 Input terminal 19 Output Terminal 20... FET 21, 22, npn) transistor 23... pnp transistor 24... c-MOS retriggerable mono multi-by-break 25... input terminal 26... output terminal 27 ...Resistance 28...Capacity or more

Claims (1)

[Claims] (1) a) A light receiving unit that receives infrared rays or other light that has been modulated by a signal and outputs the original signal, b) a photodiode, and c) connected in parallel to the photodiode in an alternating current manner. a parallel resonant circuit; d) an amplifier circuit that receives the parallel resonant circuit signal output as an input and amplifies the signal; and e) a demodulation circuit that receives the amplification circuit signal output as an input and demodulates and outputs the original signal. A light receiving unit characterized by: