JPH037175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical receiver for converting digital optical signals into electrical signals, and more particularly to an optical receiver in which a circuit is integrated on a semiconductor substrate.

An optical receiver for reproducing digital optical signals has conventionally been configured as shown in FIG. In operation, an optical signal received by a light receiving element such as a pin photodiode 1 is converted into an electrical signal, amplified by an amplifier 2, and input to a negative input terminal 6 of a voltage comparator 4. On the other hand, the reference voltage generated by the reference voltage circuit 3 is input to the positive input terminal 5 of the comparator 4, and when the magnitude of the reference voltage and the signal voltage applied to the negative input terminal 6 are reversed, a signal is output to the output terminal 7. Output. This is shown in FIG. 2, where an electrical signal 8 is applied to the negative input terminal 6 of the comparator, and a reference voltage 11 is applied to the positive input terminal 5. The electrical signal 8 consists of a DC voltage E ₀ when no light is input and a signal voltage E ₁ when light is input, and when the voltage E _ref of the reference voltage 11 and the magnitude of the electrical signal 8 are reversed, An output S is output as an output signal 13.

Generally, in an optical receiver, the output of the light-receiving element 1 is extremely small, so the difference between E ₀ and E _ref is set to about several + mV. If this happens, the DC voltage E ₀ of the electric signal 8 will fluctuate as shown in Figure 3, and there will be cases where the signal voltage E ₁ does not intersect with the reference voltage E _ref , making it impossible to obtain a normal output signal 13. . That is, for example, since the temperature dependence of the BE voltage of the transistor T _r1 of the amplifier 2 is large, the DC level E ₀ of the output signal of the amplifier 2 fluctuates greatly as the temperature rises, resulting in the state shown in FIG. 3. Become.

The present invention aims to eliminate such output instability caused by temperature fluctuations and power supply voltage fluctuations.

In order to improve the above-mentioned problems of the conventional example,
The one shown in FIG. 4 can be considered. The light receiving element 20, amplifier 21, and voltage comparator 24 have the same configuration as in FIG. The reference voltage applied to the positive input 26 of the voltage comparator 24 is generated by a reference voltage generation circuit 22 which has the same circuit configuration as the amplifier 21 and is integrated on the same semiconductor device as the amplifier 21, and a level shift circuit 23 which provides a slight offset voltage. It is provided by a reference voltage circuit consisting of: By adopting such a configuration, the DC voltage E ₀ of the electrical signal 8 which is the output of the amplifier 21 shown in FIG.
Even if the absolute value of E _ref changes due to temperature fluctuations or power supply voltage fluctuations, the relative level difference between the two does not change and a normal output signal 13 is obtained. however,
This device has problems such as malfunction of the light receiving element 20 due to a change in the DC voltage E ₀ due to a temperature change in the dark current.

FIG. 5 shows an embodiment of the present invention. A light receiving element 29 having the same structure and size as the light receiving element 20 connected to the amplifier 21 is connected to the input section 30 of the reference voltage generating circuit 22, and a light-opaque material 3 is placed on the light receiving surface of the light receiving element 29.
1. For example, by providing a black resin, the influence of changes in the DC voltage E ₀ due to temperature changes on the dark current of the light receiving element 20 is reduced. These two light receiving elements 20, 29
However, this effect is particularly large when the circuit is integrated on the same semiconductor device as other circuits due to temperature uniformity. In this embodiment, a level shift circuit is connected to the reference voltage generation circuit and an offset voltage is applied. However, it is possible to directly compare the reference voltage and the output of the amplifier without connecting the level shift circuit. Needless to say, the same effect can be obtained even if According to the present invention, it is possible to provide an optical receiver that can obtain a stable output even with respect to temperature fluctuations, power supply voltage fluctuations, and dark current fluctuations of the light receiving element.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional optical receiver, Fig. 2 is a waveform diagram showing the signal level of Fig. 1, Fig. 3 is a waveform diagram showing signal levels that fluctuate due to temperature fluctuations, etc., and Fig. 4 is a waveform diagram showing the signal level of Fig. 1. FIG. 5 is a circuit diagram showing an embodiment of the present invention. 21...Amplifier, 22...Reference voltage generation circuit,
24... Voltage comparator, 20, 29... Light receiving element,
31...Light opaque substance.

Claims (1)

[Claims] 1. An amplifier that amplifies the output of the first light-receiving element; A reference voltage generation circuit that outputs a reference voltage and is configured of the same DC circuit as this amplifier; and connected to this reference voltage generation circuit. a second light-receiving element having the same function as the first light-receiving element and having a light-receiving surface covered with a light-opaque material; and a comparator for comparing the output of the amplifier and the reference voltage. An optical receiver characterized by: