JPH021634A - optical receiver circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical receiving circuit particularly suitable for optical space communication.

[Background of the invention]

A generally known optical receiver circuit is JP-A-58-
As described in Japanese Patent No. 142647, there is a photocurrent voltage conversion circuit in which a light receiving element and an amplifier circuit with low input impedance are connected. However, when this circuit is used for optical space communications that are affected by external noise light such as sunlight and lighting, the following problems arise.

(1) Generally, an optical signal modulated at a high frequency is converted into an electrical signal by a light-receiving element, but noise such as hum occurs because the DC component from sunlight and the light from lighting are modulated at the power frequency. Therefore, it is necessary to provide a complicated filter circuit at the subsequent stage.

(2) Especially when a large amount of direct current is generated from the light receiving element, the light receiving element becomes saturated and reception becomes impossible.

[Purpose of the invention]

An object of the present invention is to remove external noise optical components generated in a light receiving element in order to stably receive optical signals even in a communication environment with strong external noise light such as sunlight and lighting in optical space communication. The object of the present invention is to provide a functional optical receiving circuit.

[Summary of the invention]

The present invention automatically absorbs low frequency components including direct current and hum generated in the light receiving element in an optical receiving circuit that connects a light receiving element and an amplifier with low input impedance, and absorbs high frequency components of an optical signal. By providing a bias control circuit exhibiting high impedance, only the optical signal current can be converted into voltage by an amplifier circuit with low input impedance.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The figure is a circuit diagram showing the basic configuration of the present invention, in which 1 is a light receiving element represented by a diode, 2, 3, 4 are transistors, 5, 6, 7.8 are resistors, 9 is a capacitor, 10 is a power supply terminal, and 11 is an output terminal.

Diode 1 is a common emitter transistor 2
and an amplifier circuit composed of a transistor 3 whose collector is grounded. Note that the above-mentioned amplifier circuit is configured to apply feedback using a feedback resistor 5, and has a low input impedance. Also, ground the emitter and connect the base to 1-
The collector of the transistor 4 connected to the emitter of the transistor 2 is connected to the input terminal of the amplifier circuit, and the capacitor 9 for AC bypass is connected between the base of the transistor 4 and the ground, so that the high frequency region of the optical signal component is sufficiently The low impedance is designed to have a sufficiently high impedance in the low frequency region, which is the main component of external noise light.

Optical signals and external noise light such as sunlight or illumination light are converted into current by the photodiode 1.

First, we will explain the DC r current generated by sunlight. This photocurrent flows into the base of transistor 2 and increases the emitter potential of transistor 2. As a result, the base current of transistor 4 increases, and the photocurrent increases. As the collector current of transistor 4 increases, the base current of transistor 2 decreases, and the emitter potential of transistor 2 is maintained at V++R (voltage between the base and emitter of transistor 4). ] 4 will be bypassed by transistor 4, and the collector potential of transistor 4 will be 2V regardless of the degree of photocurrent.
n2 (voltage between the base and emitter of transistor 2 and transistor 4). This means that the photodiode 1 is biased at a constant level, so that the photodiode 1 will not become saturated and become unable to receive data.

Regarding low frequency noise current including hum generated by lighting, etc., the capacitor 9 has a high impedance in the low frequency region, so a low frequency noise voltage is generated at the emitter of the transistor 2. Therefore, the low frequency noise current generated in the photodiode 1 is also bypassed by the transistor 4.

On the other hand, regarding the signal current generated by the optical signal, the capacitor 9 has a low impedance in the signal frequency region, and no signal voltage is generated at the emitter of the transistor 2.

Therefore, since the impedance between the collector and emitter of the transistor 4 is high, the signal current generated by the photodiode 1 is converted into a signal voltage by an amplifier circuit with a low input impedance composed of the transistors 2 and 3. This signal voltage ■. is the value shown by the following equation.

V 04 Iin It is now possible to remove external noise light components with a simple circuit configuration, and even in communication environments with a lot of external noise light in optical space communications, the SN ratio is generally improved by 20 dB or more compared to conventional circuits.
This has the effect of expanding the communication distance.

[Brief explanation of the drawing]

The figure is a circuit diagram of a basic configuration showing an embodiment of the present invention. 1... Photodiode 2, 3.4... Transistor 5.6, 7.8... Resistor 9... Capacitor 10... Power supply terminal 11... Output terminal

Claims (1)

[Claims] In an optical receiving circuit that connects a first transistor with a common emitter to a second transistor with a common collector and applies feedback to the light receiving element to convert an optical signal into an electrical signal, the emitter is grounded. By connecting the collector of a third transistor whose base is connected to the emitter of the first transistor constituting the amplifier circuit to the input terminal of the amplifier circuit, an external noise optical component generated in the light receiving element is removed. An optical receiving circuit characterized in that it is configured as follows.