JPH0258819B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light receiving device used in a remote control device, and is particularly designed to prevent malfunction due to external noise.

Conventionally, there are two types of remote control devices for television receivers: one uses ultrasonic waves as a communication medium, and the other uses infrared rays. Since methods using ultrasonic waves often malfunction in response to ultrasonic components such as from a telephone ringing, methods using infrared rays have recently been widely used. For remote control, pulse codes are sent and received corresponding to functions such as power on/off and channel switching. In the method using infrared rays, infrared rays with a wavelength of 900 nm to 1000 nm are transmitted at several tens of kilohertz.
The signal is modulated at a frequency m, and sent and received using a pulse code of several bits, and a microcomputer on the receiving side processes the code signal to obtain a remote control signal. An example of a remote control signal is a pulse modulated infrared carrier wave, as shown in FIG. A light receiving circuit that receives such a signal is configured as shown in FIG. A light receiving element 2 that receives infrared rays 1 has one end connected to a power supply terminal 3 to form a light receiving section 4, and the other end is connected to a field effect transistor TR via an amplitude limiting circuit 5 for buffering and amplification with a transistor _TR1 . ₂ , and the remote control signal amplified by this amplifier circuit 6 is input to a first selection amplifier circuit 7 at the next stage. This first selection amplifier circuit 7 is a tuning circuit, and a signal near the modulation frequency m of the remote control signal is selectively outputted by an inductive coupler _L1 provided on the collector side of the transistor _TR3 , which is the main part. be. Subsequently, the output of this circuit is level-adjusted by a level adjustment circuit 8 constituted by a transistor TR ₄ , and is input to a second selection amplification circuit 9 at the next stage. This second selection amplifier circuit 9 also includes a transistor TR ₅ and an inductive coupler L ₂
A signal near the modulation frequency m is selected and output to the output amplification circuit 10.
This output amplification circuit is composed of a complementary circuit of transistors TR ₆ and TR ₇ , and rectifies and shapes the incoming waveform to form a required code signal at the output terminal 11.

In the above circuit, the code signal at the output terminal 11 is guided to the pulse generating section of the tuning circuit, undergoes the code signal processing as described above, and is converted into a tuned output. The first and second selection amplification circuits 7 and 9 have characteristics of sharp selectivity to prevent frequency components of external noise from being mixed into this output signal, and accurately respond to the infrared transmission signal, resulting in erroneous judgment output. becomes difficult to obtain.

Incidentally, in recent years, fluorescent lamps that are lit by an inverter circuit have been commercially available for the purpose of power saving.
This fluorescent lamp generates a high frequency wave using an inverter circuit, and is turned on by this high frequency wave. However, since the frequency a of this inverter circuit is close to the modulation frequency m of the remote control signal of the television receiver, this light receiving circuit amplifies the light from the fluorescent lamp and does not work with the original remote control signal. This problem has started to occur.

Therefore, the selectivity Q of the inductive couplers L ₁ and L ₂ of the first and second selection amplifier circuits 7 and 9 is further increased.
It was considered to make the other components as narrow as possible, but since there is also a temperature drift of the tuning point,
Naturally, there are limits and it is not possible to deal with them adequately. That is, the modulation frequency of the infrared light emitted from the fluorescent lamp.
a is the modulation frequency m of the remote control signal
If they match, there is no way to increase Q to eliminate the interference waves. In addition, the amplification degree of the above-mentioned light receiving circuit is fixed, and the total gain of the circuit is set to 100 [dB] or more so that the signal can be received even if the remote control signal is weak.
For example, the output amplitude in the second selection amplifier circuit 9 becomes saturated. Therefore, even if the above-mentioned interference signal from the fluorescent lamp is weak, there is no difference in amplitude between it and the regular remote control signal, and the interference signal may be responded to. In other words, as shown in Figure 3, the input/output characteristics of the photodetector circuit described above are such that when the input amplitude exceeds point a shown in the figure, whether it is an interference wave or a regular remote control signal, it is amplified to a constant amplitude. This can cause the device to stop responding to legitimate remote control signals or malfunction.

This invention has been made in view of the above-mentioned points, and by periodically changing the gain of a circuit that receives remote control signals in synchronization with the power supply frequency, it is possible to use It is an object of the present invention to provide an optical receiver capable of receiving a regular remote control signal even if a noise source emitting modulated infrared rays is taken in.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 4 is a circuit diagram according to an embodiment of the present invention. Before explaining the details of the circuit, the principle of the present invention will be described with reference to FIG. 5. In each waveform in FIG. ₅ , the horizontal axis represents time and the vertical axis represents signal _amplitude .
This is the output waveform when a signal from a fluorescent lamp is received. The lower signal _S2 indicates the power frequency waveform of the commercial AC power source.
As described above, it has been experimentally confirmed that when the conventional circuit receives light from a fluorescent lamp, the amplitude change of the output waveform signal _S1 has a constant phase relationship with the period of the power supply frequency waveform _S2 . In other words, the maximum amplitude of signal S ₁ is the power supply waveform
It appears periodically with a certain phase relationship with the amplitude change of S ₂ . Therefore, the signal S ₃ at the output terminal 11 of the light receiving circuit becomes, for example, a positive pulse waveform in synchronization with the maximum amplitude of the signal S ₁ in the light receiving circuit. This pulse _S3 is input to the microcomputer built in the channel selection circuit after the light receiving circuit, and becomes an obstacle for the microcomputer to determine the correct code signal. The present invention is characterized in that the signal S ₁ in the light receiving circuit when receiving the interfering light beam that is the basis of the pulse signal S ₃ becomes periodic as shown in FIG. 5, and is synchronized with the cycle of the power supply. By lowering the gain of the light receiving circuit only during periods when the amplitude of the interference light beam is large, the interference signal is eliminated and only the remote control signal based on the regular infrared rays is extracted.

The configuration of FIG. 4 will be explained. Note that the same elements as in the conventional circuit are given the same reference numerals. The light-receiving element 2 is an element that photoelectrically converts infrared rays 1, and is configured such that the DC voltage supplied from the feed end 3 of the constant voltage circuit 21 is bias-adjusted and always applied, and the photoelectric conversion signal is transmitted to the amplitude limiting circuit 5. The collector output is inputted to the base of the transistor _TR1 , and the collector output is returned to the base and output to the next stage amplifier circuit 6.
The amplifier circuit 6 is, for example, a junction field effect transistor.
The transistor TR ₂ is connected to the base of the transistor TR ₃ that constitutes the first selection amplification circuit 7. An inductive coupler _L1 is inserted into the collector of the transistor _TR3 , and is coupled to the level adjustment circuit 8 at the next stage. The inductive coupler L ₁ is set to take out the modulation frequency m component of the remote control signal,
The device is configured to eliminate interfering signal components other than the remote control signal. Furthermore, a switching circuit 22 composed of a transistor _TR8 for deriving a gain control signal _S6 , which will be described later, is connected to the base of the transistor _TR3 .

This switching circuit 22 is coupled to a phase shifter 24 via an adjustment resistor 23, takes in the output signal _S5 , and detects the amplitude peak portion of the signal _S5 . The phase shifter 24 is connected to a voltage dividing circuit 26 that divides and detects a rectified signal S ₄ obtained by full-wave rectification of the AC power source 25, for example. In detail below, the AC power supply 25 connects the transformer 27 to the same pole of each of the rectifying diodes _D1 to _D4 via the transistor 27.
Both ends of the secondary coil are connected. The center tap of the secondary coil is grounded and the rectifier diode
The other electrode of D ₁ and D ₄ is a smoothing capacitor C ₁
The other electrodes of the rectifying diodes D ₂ and D ₃ are connected to each other through resistance.
The voltage divider circuit 26 consists of R ₁ and resistor R ₂ in series.
is grounded through. These voltage dividing resistors R ₁
The connection point between and R ₂ is capacitor C ₂ and adjustment resistor R ₃
It is connected to the base of the transistor _TR8 constituting the switching circuit 22 through a series connection of a phase shifter 24 and an adjustment resistor 23. The transistor _TR8 has a base resistor _R4 , and a collector is grounded via a resistor _R5 . The output of the constant voltage circuit 21 is used as the power supply voltage of the transistor _TR8 , that is, the power supply end 3 is connected to the emitter of the transistor _TR8 via a resistor _R6 . Also, the emitter of transistor TR ₈ is resistor R ₇
is grounded by The output terminal of the switching circuit 22 is connected to the base of the transistor _TR3 constituting the first selection amplifier circuit 7 via a resistor _R8 .

As described above, the collector output of the transistor TR ₃ controlled by the transistor TR ₈ is led to the output terminal 11 via the level adjustment circuit 8, the second selection amplifier circuit 9, and the output amplifier circuit 10, which have the same configuration as the conventional ones. , it is designed to output a code signal for remote control.

The optical receiving device of the present invention is configured as described above. Next, this effect will be explained. As described in the above basic operation, in this embodiment, the gain of the signal detected by the light receiving element 2 is controlled in synchronization with the cycle of the power supply 25 in the first selective amplification circuit 7. However, as shown in Fig. 5, the light receiving circuit signal S ₁ based on the interference signal from the fluorescent lamp
The peak of AC power supply 25 has a phase difference of several tens of degrees. For example, this is due to the switching characteristics of an inverter circuit that blinks a fluorescent lamp. Therefore, even if the gain of the light receiving circuit is controlled with the same phase relationship, the signal S ₁ in the light receiving circuit
Since the peak of the power supply is not synchronized with the peak of the noise, it is not possible to eliminate the interference factor.

Therefore, in the optical receiving device of the present invention, the alternating current signal S ₂ from the power supply 25 is, for example, full-wave rectified, and the rectified output S ₄ with a large amount of drift is detected as a divided voltage, and then the phase shift amount is adjusted by the phase shifter 24 . The phase shifter 24 has a phase shift amount Θ determined by Θ=tan ^-1 (1/2πC ₂ R ₃ ), and the phase shift amount Θ is changed by changing the value of the resistor R ₃ .
Adjust the phase of rectified output S ₄ input to rectified output S ₅
The peak of the rectified output S ₄ is made to match the peak of the signal S ₁ in the light receiving circuit by adjusting the phase. This phase-adjusted output S ₅ forms the gain control signal S ₆ of FIG. 5 from the collector of the transistor TR ₈ of the switching circuit 22 via the adjustment resistor 23. That is,
At the peak of the adjusted rectified output S ₅ the transistor TR ₈
is turned off and its collector level is set to a low level, which is approximately the same level as the base potential of transistor TR ₃ , and transistor TR ₈ is turned on except at peak times, and is determined by resistor R ₆ , resistor R ₅ , and resistor R ₇ . By applying a high level voltage to the base of the transistor _TR3 , the gain of the first selection amplifier circuit 7 is lowered when the gain control signal _S6 is at a low level, and is increased when the gain control signal S6 is at a high level. This makes it possible to reduce the signal at the peak of the signal _S1 in the light receiving circuit based on the interference signal.
The selective amplification circuits 7 and 9 selectively amplify only the signals based on the original remote control signal, and do not send erroneous pulse code signals to the channel selection circuit.

Note that the gain control signal _S6 can be applied to any amplification stage in the light receiving circuit, and may be controlled over several stages in some cases. It is also possible to directly amplify the output of the adjusted rectified output _S5 , which is the output of the phase shifter 24, and use it as a signal for gain control.

As described above, according to the present invention, the gain of the light receiving circuit is changed periodically in synchronization with the power supply, so that interference signals such as infrared rays generated in synchronization with the power supply can be used as regular remote control signals. It is possible to provide a remote control device that is free from the risk of malfunction even if the remote control device is mixed with the device.

[Brief explanation of the drawing]

Figure 1 is a diagram showing remote control signals;
FIG. 2 is a circuit diagram showing a conventional light receiving circuit, FIG. 3 is an input/output characteristic diagram of the circuit shown in FIG. 2, FIG. 4 is a circuit diagram of an optical receiving device according to the present invention, and FIG. FIG. 2 is an operation waveform diagram illustrating the operation of FIG. 2... Light receiving element, 3... Feeding end, 4... Light receiving section, 5... Amplitude limiting circuit, 6... Amplifying circuit, 7...
...First selection amplification circuit, 8...Level adjustment circuit, 9
... second selection amplification circuit, 10 ... output amplification circuit,
11... Output terminal, 21... Constant voltage circuit, 22...
...Switching circuit, 23...Adjustment resistor, 24...
...Phase shifter, 25 ... AC power supply, 26 ... Voltage divider circuit, TR ₁ to _{TR 8} ... Transistor, D ₁ to _{D 4} ...
Diode, L ₁ - L ₂ ... Inductive coupler, C ₂ ... Capacitor, R ₁ - _{R 8} ... Resistor.

Claims (1)

[Claims] 1. An optical medium having a modulation frequency is transmitted as a pulse code signal, which is received by a light-receiving element and converted into an electrical signal, and this electrical signal is amplified by an amplifier circuit to obtain the modulation frequency. In an optical receiver equipped with a light receiving circuit that inputs a signal to a tuned circuit with frequency selectivity and shapes the output of this tuned circuit to extract a desired code signal, a commercial AC power source and a voltage of this AC power source are used. rectifying means for performing full-wave rectification; phase shifting means for shifting the rectified output from the rectifying means by a constant phase in order to synchronize the rectified output from the rectifying means with a disturbance signal having a constant phase relationship with the cycle of the AC power source; detection means for detecting periodic amplitude peak portions of the output of the light receiving circuit, and controlling the gain of the light receiving circuit to be lowered during the period of the interference signal in response to the detection signal of the detection means. 1. An optical receiver comprising gain control means.