JPS623951Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an optical receiver used in a remote control device, and is particularly designed to prevent malfunctions due to external noise.

Conventional remote control devices for television receivers include methods that use ultrasonic waves as a communication medium and methods that use infrared rays as a communication medium. 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 in response 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 KHz.
The signal is modulated by a pulse code of several bits and transmitted and received, and a microcomputer on the receiving side processes the code signal to obtain remote control.
An example of a remote control signal is a pulse modulated infrared carrier wave, as shown in FIG. A receiving device for receiving such signals is constructed as shown in FIG. 2, and the infrared rays 11 are converted into electrical signals by the light receiving element D. In Fig. 2, 12 is a limiter, 13,
14, 15, 16 are first to fourth stage amplifier circuits, 1
7 is a tuning circuit, 18 is a rectifier circuit, 19 is a waveform shaping circuit, and 20 is a level shift circuit. A code signal is derived from the output terminal 21, and is input to a microcomputer and processed. Further, 22 is a power supply terminal.

In the above circuit, the coil of the tuning circuit 17 is tuned to the modulation frequency m, so that only the m component of this circuit can be extracted. Here, as the Q of the tuning circuit 17 is increased, the frequency selectivity characteristic becomes sharper, so that this circuit accurately responds to the infrared transmission signal, and it becomes difficult to obtain an erroneous determination output.

However, in recent years, there are fluorescent lamps that are equipped with switching circuits using transistors and have improved luminous efficiency. The energy emitted from this fluorescent lamp is mainly visible light, but it also contains a considerable amount of infrared rays. This infrared ray is modulated at several tens of KHz, and its modulation frequency a is close to the modulation frequency m of a so-called remote control signal used for remote control. For this reason, the receiving circuit may also respond to light from a fluorescent lamp, resulting in malfunction. In order to prevent this, the tuning circuit 1
It was considered to increase the selectivity characteristics of 7 and increase the Q, 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. Assuming that the modulation frequency a of the infrared rays emitted from the fluorescent lamp matches the modulation frequency m of the remote control signal, the interference waves cannot be removed no matter how high the Q is. Furthermore, the amplification degree of the receiving circuit is fixed, and the overall 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. Therefore, even if the interference signal from the above-mentioned fluorescent lamp is weak, it may be responded to. In other words, as shown in FIG. 3, the input/output characteristics of the above receiving circuit are such that the input amplitude is a
If this point is exceeded, whether it is an interference wave or a legitimate remote control signal, it will be amplified to a certain amplitude, resulting in a complete failure to respond to legitimate remote control signals or malfunctions.

This idea was made in view of the above circumstances, and it is possible to automatically adjust the amplification degree internally according to the amplitude of the remote control signal, and even when interference signals are mixed in, the above-mentioned legitimate remote control signal can be detected. It is an object of the present invention to provide an optical receiving device capable of detection.

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

FIG. 4 shows a first embodiment of this invention, and the same parts as in FIG. 2 will be described with the same reference numerals. That is,
The signal photoelectrically converted by the light-receiving element D is amplitude limited by a limiter 12 made up of a transistor _TR1 , and is input to an amplifier circuit ₁₃ made up of a transistor TR2. The signal amplified by this amplifier circuit 13 is tuned through sequentially the amplifier circuit 14 composed of the next transistor TR ₃ , the amplifier circuit 15 composed of the transistor TR ₄ , and the amplifier circuit 16 composed of the transistor TR ₅ . Input terminal 1 of circuit 17
7 ₁ is supplied. The primary coil _L1 of this tuned circuit 17 has one input terminal ₁₇₁ connected to a transistor.
It is connected to the collector of TR ₅ , and the other terminal ₁₇₂ is connected to the power supply line. The signal frequency-selected by the tuning circuit 17 has its high frequency components removed in the rectifier circuit 18, and is input to the waveform shaping circuit 19 as a pulse output. The waveform-shaped output by transistors TR ₆ and TR ₇ is
The signal is level-shifted by the transistor TR ₈ and delivered to the output terminal 21 as a pulse code signal.

Furthermore, a gain control circuit is provided to the above circuit configuration. That is, diode 31, resistor 3
2. The capacitor 33 constitutes a detection and integration circuit for the signal at the input terminal ₁₇₁ of the tuning circuit 17. Here, when a remote control signal appears in the coil of the tuning circuit 17, by appropriately selecting the value of the capacitor 33, an output as shown by the solid line in FIG. 5 appears at the base of the transistor _TR10 . This output level increases as the amplitude of the remote control signal increases, and the base potential of the transistor _TR10 increases. That is, the output of the detection and integration circuit is applied via resistor 34 to the base of transistor _TR10 . The collector of the transistor _TR10 is connected to the power supply line, and the emitter is connected to the base of the transistor _TR11 . The connection configuration of the transistors TR ₁₀ and TR ₁₁ is to increase the base input impedance of the transistor TR _10. If the base input impedance is low, the capacitor 33 will be discharged immediately and the base potential of the transistor TR ₁₀ will fluctuate. This is because it will be put away. transistor
If the remote control signal detection circuit using TR ₁₀ and TR ₁₁ does not operate at a rising speed of several 100 μsec, it will not be able to fully respond to a remote control signal with a width of several milliseconds, so the capacitor 3
The capacitance of transistor TR10 cannot be increased very much, and it is necessary to increase the discharge time constant to keep the base potential of transistor _TR10 constant.
The base input impedance of TR ₁₀ must be large.

The collector of the transistor _TR11 is connected to the power supply line, and the emitter is connected to the reference potential terminal via a resistor 35 and to the base of the transistor _TR12 via a resistor 36. The base of this transistor _TR12 is connected to the reference potential terminal via a variable resistor 37. The emitter of this transistor _TR12 is connected to the power supply line via a resistor 38 and to a reference potential terminal via a resistor 39. This transistor 39
The collector of the amplifier circuit 1 serves as a control signal output section.
It is connected to the control terminal of 4.

When the base potential of the transistor _TR10 becomes high and turns on, the transistor _TR11 also turns on, and the emitter potential of the transistor _TR11 becomes high. As a result, the base potential of the transistor _TR12 also increases, and the emitter-collector resistance of the transistor _TR12 increases. Therefore, the base bias resistance of transistor TR ₃ increases, and the amplification degree of transistor TR ₃ decreases. In the presence of a noise source such as a fluorescent light, the result is that the noise amplitude appearing in the coil of the tuned circuit 17 is reduced.
By operating in this way, only the remote control signal appears at the terminal 21 that supplies the code signal to the microcomputer.
It is possible to perform normal remote control operation even if there is some noise.

FIG. 6 shows another embodiment, in which the collector output of transistor TR ₁₂ is used to control the base bias of transistor TR _4.Other operations are the same as in the previous embodiment, with a certain amplitude Only when the above remote control signal is input, the gain of the transistor TR ₄ is lowered to reduce the noise output amplitude appearing at the coil of the tuning circuit 17. FIG. 7 shows still another embodiment, in which the gain of the transistors TR ₃ and TR ₄ is controlled by the collector output of the transistor TR ₁₂ .

FIG. 8 shows yet another embodiment, in which the detection and integration circuit is composed of a diode 31, a resistor 32, a capacitor 33, and a resistor 40, and the output is
It is input to the gate of the field effect transistor 41. The drain variable resistor 4 of this transistor 41
The transistor TR 13 is connected to the power supply line via a resistor 43, and to the base of a transistor TR ₁₃ via a resistor 43. Further, the source of the field effect transistor 41 is connected to the reference potential end via a diode 44 in the opposite direction, and is also connected to the power supply line via a resistor 45. The emitter of the transistor _TR13 is connected to the reference potential terminal, and the base is connected to the resistor 4.
6 to the reference potential end, the collector is
It is connected to the power supply line via a resistor 47 and to the base of the transistor _TR14 . The emitter of this transistor _TR14 is connected to the power supply line, and the collector is connected to, for example, a control terminal of the amplifier circuit 14. The circuit according to this example also
The remote control signal detection means and gain control means operate in the same manner as in the previous embodiment. That is, when there is a remote control signal of a certain amplitude or more, the gate voltage of the field effect transistor 41 becomes high and turns off, and the drain voltage thereby becomes low and the transistor _TR13 turns off. At this time, the base voltage of the transistor _TR14 increases, its emitter-collector resistance increases, the base bias current of the transistor _TR3 decreases, and the amplification factor decreases.

As mentioned above, this invention is an optical receiver that can automatically adjust the amplification level internally according to the amplitude of the remote control signal, and can detect legitimate remote control signals even when interference signals are mixed in. can be provided.

[Brief explanation of the drawing]

Figure 1 is a diagram showing remote control signals;
Fig. 2 is a circuit diagram of a conventional optical receiver, Fig. 3 is an input/output characteristic diagram of the circuit shown in Fig. 2, Fig. 4 is a circuit diagram showing an embodiment of this invention, and Fig. 5 is a The detection characteristic diagram of the circuit shown in the figure, and FIGS. 6, 7, and 8 are circuit diagrams showing other embodiments of this invention, respectively. D... Light receiving element, 12... Limiter, 13-16...
Amplifier circuit, 17... Tuning circuit, 18... Rectifier circuit, 1
9...Waveform shaping circuit, 20...Level shift circuit, 3
DESCRIPTION OF SYMBOLS 1...Diode, 32...Resistor, 33...Capacitor, _TR10 , _TR11 , _TR12 , _TR13 , _TR14 ...Transistor, 41...Field effect transistor.

Claims (1)

[Scope of utility model registration request] 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, which is amplified by an amplifier circuit, and a frequency selection characteristic is set to the modulation frequency. In an optical receiving device, the signal amplitude input to the tuning circuit is an optical receiver comprising: means for detecting the signal using a detection and integration circuit; and gain control means for lowering the gain of the amplitude circuit when the signal amplitude exceeds a certain amplitude level according to the output of the detection means. Device.