JPS6114447B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal receiving device for a remote control device using infrared signals.

A conventional infrared signal receiver has the configuration shown in FIG. 1, for example, and when modulated infrared light is incident on the infrared light detection element 1, a current flows through the infrared light detection element 1. The signal current flowing through the infrared light detection element 1 is converted into a voltage by an LC tuning circuit 2 tuned to the transmission signal carrier frequency, amplified by a first amplification circuit 3 and a second amplification circuit 4, and then converted to a voltage by a detection circuit. It is demodulated by 5. In the conventional circuit, when natural light other than the signal, disturbance light from an incandescent light source, etc. enters the infrared light detection element 1, a noise current flows through the infrared light detection element 1, and the signal frequency tuned to the LC tuning circuit 2 is generated. The component noise is amplified and input to the detection circuit 5. When this noise becomes large, the input of the detection circuit 5 becomes saturated with the noise, making it impossible to distinguish between the signal and the noise. Therefore, if the communication distance by infrared light is increased and the reception sensitivity to the signal is increased, that is, if the gain of the amplifier circuits 3 and 4 is increased, the infrared light detection element 1 becomes more sensitive to noise.
It has the disadvantage that communication becomes impossible if even a small amount of disturbance light other than signals is incident on it. If the gains of the amplification circuits 3 and 4 are limited under the worst conditions of disturbance light, it becomes necessary to unnecessarily increase the transmission energy of the infrared signal in order to increase the communication distance under practical disturbance light. , the power consumption on the light transmitting side is large, which is extremely disadvantageous for remote controls that operate on dry batteries, etc. Therefore, it is conceivable to provide an automatic gain control circuit that limits the gain according to the noise level of the outputs of the amplifiers 3 and 4, so as to always suppress the noise entering the input of the detection circuit 5 to a certain amount or less. This method is effective for natural light and incandescent lamps, but for pulsed incident light from fluorescent lamps, it is difficult to use due to the noise of the tuned frequency component contained in the incident light and passing through the LC tuning circuit. It has the disadvantage that automatic gain control is applied too strongly under the same illuminance as incandescent lamps. If a circuit with a high ability to discriminate between pulse noise and signals, for example a circuit with a high ability to remove noise such as fluorescence, is adopted as the detection circuit 5, the gain control circuit described above will perform unnecessary gain control, resulting in a loss of communication distance. become.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a receiver amplifier with automatic gain control suitable for combination with a detection circuit that is resistant to fluorescent lamp noise.

In order to achieve the above object, the present invention detects the magnitude of the infrared component of the disturbance light based on the magnitude of the current flowing through the infrared detection element, distinguishes fluorescent lamp noise from incandescent lamp noise, etc. Automatic gain control is disabled for noise.

FIG. 2 is a block diagram showing an embodiment of the present invention. The structure is such that a direct current flowing due to disturbance light incident on the infrared detection element 1 is detected as a voltage drop across a resistor 6, and an automatic gain control circuit 8 is turned on and off by a transistor switch 7.

That is, when the current flowing through the resistor 6 increases and the voltage across the resistor 6 becomes larger than the base-emitter voltage of the transistor 7, the transistor 7 is turned on.

Here, this receiver has a signal carrier frequency
It receives a 1 mSec repeated signal modulated at 40KHz, amplifies it, detects it, and demodulates it into a 1 mSec repeated pulse. The detection circuit 9 integrates the signal twice with two time constants: τ ₁ =40 μSec and τ ₂ =400 μSec. As a result, even if the amplitude of the pulse output from the amplifier 4 is large, fluorescent lamp noise with a repetition frequency of 3 to 7 KHz is not output as demodulated output. The white noise that appears at the output of the amplifier 4 due to the incidence of light such as an incandescent lamp is reduced to a level that does not affect the demodulated output at the input of the detection circuit 9. A gain control circuit 8 for controlling gain is provided. By stopping the operation of the gain control circuit 8 when fluorescent lamp noise is input, the resistor 6 detects the direct current flowing through the infrared detection element, and the automatic gain control circuit 8 is turned on and off.

This means that the current induced in the infrared detection element 1 by a typical light source under the same illuminance is proportional to the infrared component of the light source, and the ratio of the two is approximately, assuming that an incandescent light source (tungsten lamp) is 1. Fluorescent lights take advantage of the fact that it is approximately 0.1. As a result, under ambient light of the same illuminance, a maximum gain is obtained without gain control in a fluorescent lamp, and a gain under gain control is obtained in an incandescent lamp. Under fluorescent lights, the noise is amplified as it is, but the detection circuit 9 is resistant to fluorescent light noise.
can take advantage of the properties of 3, 4, and 5 compare the relationship between communication distance and disturbance light for a circuit without gain control, a receiving circuit using conventional gain control, and a receiving circuit using gain control according to the present invention. Since the communication distance is proportional to the infrared energy on the transmitting side, it is normalized by l, and the tolerance to disturbance light illuminance is inversely proportional to the gain of the amplifiers 3 and 4, so it is normalized by E. Each transmits the same energy and uses an amplifier with the same maximum gain. Third
As shown in the figure, in the case of fixed gain, when the illuminance becomes high under incandescent lamps, the input of the detection circuit 9 becomes saturated with noise and becomes uncontrollable. Under fluorescent light, the detection circuit 9 is resistant to fluorescent light noise, so the communication distance will not be impaired.

FIG. 4 shows automatic gain control applied to the output of the amplifier 4, and for incandescent lamps, a communication distance that is inversely proportional to the disturbance illuminance can be obtained. Fluorescent lamps are subjected to too much gain control, which impairs communication distance.

FIG. 5 shows the characteristics of the receiver according to the present invention, which combines the better performances shown in FIGS. 3 and 4.

As explained above, according to the present invention, it is possible to maximize the capabilities of the receiver both under fluorescent light and incandescent light.
It is possible to provide a receiver that is not affected by noise caused by disturbance light.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional circuit, and FIG. 2 is a block diagram showing an embodiment of a receiving circuit according to the present invention.
FIG. 3, FIG. 4, and FIG. 5 are characteristic diagrams. 1: infrared detection element, 3, 4: amplifier, 7: transistor (switch circuit), 8: automatic gain control circuit.

Claims (1)

[Claims] 1. An infrared light detection element, an amplifier for amplifying its output signal, and an automatic gain control circuit connected to reduce the gain of the amplifier as the output noise of the amplifier increases. An infrared signal receiver comprising: a switch circuit that turns on and off by detecting a direct current flowing through the infrared light detection element; and an output of the switch circuit intermittents the operation of the gain control circuit.