JPS5873251A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To simplify the constitution of a photo reception circuit, by using a constant current source for a bias power supply of an avalanche photo diode. CONSTITUTION:An avalanche photo diode 11 converts an optical pulse train into an electric pulse train. A constant current source 13 reverse-biases the diode 11. Then, since the output current of the diode 11 is kept constant, the amplitude to an output signal of the diode 11 is constant independently of the characteristic change of the diode 11 due to the input optical signal amplitude and temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION In particular, avalanche photodiodes (abbreviated as AP)
The present invention relates to an optical receiving circuit using an optical receiver (also referred to as D).

Conventional optical pulse receiving circuits often use an APD having an amplifying effect as a light-to-electricity conversion element. The APD is used with a reverse bias, and its multiplication factor M is changed by changing the noquious voltage.

However, when the value of M is increased, the noise generated from inside the APD corresponding to M is also multiplied, so just because the multiplication factor M is large does not necessarily improve the signal-to-noise ratio of 87M.
There is a certain value of M for which 7M is the best. Also, as will be explained in detail later, the bias voltage vs. multiplication factor M characteristic of the APD changes greatly with temperature.
needs to be constant.

Further, it is desirable that the output signal of the optical receiving circuit has a constant amplitude regardless of the magnitude of the input optical signal for the operation of the electric circuit thereafter. For this reason, the APD is adjusted according to the size of the input optical signal.
It is necessary to change the multiplication factor M and keep the output of the optical receiving circuit constant.

Conventionally, in order to satisfy the above two requirements.

As will be explained in detail later, the amplitude of the output of the optical receiver circuit is detected by a peak detection circuit, the detected value is compared with a reference voltage, and the reverse bias voltage of the APD, that is, M, is determined from the error voltage. A method is adopted in which the output of the optical receiving circuit is kept constant regardless of changes due to the size of the APD or the temperature of the APD.

FIG. 1 is a block diagram of the conventional optical receiver circuit explained above, in which 1 is an APD p, 2 is an amplification circuit, 3 is a peak detection circuit, 4 is a DC amplification circuit, and 5 is a DC amplification circuit. A DC/D conversion circuit whose output voltage changes, 6 represents an optical input terminal, 7 represents a receiving circuit output terminal, and 8 represents a reference voltage terminal. In the circuit shown in FIG. 1, the peak value of the output is detected by the amplifier circuit 3 and the reference voltage (V
□F), and the error voltage is converted into an APD bias voltage by the DC/DC converter 5 to increase the APDO multiplication factor.

It operates to keep the amplitude of the output terminal 7 constant.

The present invention uses a circuit configuration that maintains the amplitude of the receiving circuit output constant without configuring a large control loop including an amplification circuit as in the conventional system.

If the code of the optical transmission line is a DC-balanced code, the DC component of the code is constant regardless of the type of information. AP
D has the function of converting the input optical signal into a current, so if a DC balanced optical signal 4) response train is input as input light, it will convert depending on the amplitude of the input optical signal. AP
Since the output current of D changes and the wear rate etc. changes, APD
It is clear that the output current and the amplitude of the light/2 lux do not have a one-to-one correspondence.

From the above, if the APD bias power source is a constant current source, 1. Even if the magnitude of the input optical signal or the characteristics of the APD change due to temperature, the output current (output amplitude) of the APD remains constant, that is, the output of the receiving circuit remains constant, and the system performs the same function as the conventional system.

FIG. 2 is a diagram showing an outline of the configuration of an optical receiving circuit according to the present invention, in which 11 is an APD and 12 is an amplification circuit.

13 represents a constant current power supply, and 14 represents an optical input terminal.

15 represents a receiving circuit output terminal. In this configuration, the APD output current is kept constant by 13 constant current sources, so
The amplitude of the APD output signal remains constant regardless of the input optical signal amplitude and changes in APD characteristics due to temperature.

FIG. 3 is a diagram showing an example of a detailed configuration of the receiving circuit according to the present invention shown in FIG. 26 is a resistor, 27 is an optical input terminal, 28 is an output terminal, and 29 is a reference voltage input terminal. In this example.

The current flowing through the APD 21 is converted into a voltage by the resistor 26 and detected, the detected voltage is amplified by the DC amplifier circuit 23, and the error signal, which is the difference voltage between the voltage of the amplified signal and the reference voltage vREF, is sent to the DC amplifier circuit. 24 and operates the DC/DC conversion circuit 25, so that the current flowing through the APD 21 is kept constant.

As explained above, by using a constant current source as the bias power source of the APD, the configuration of the optical receiving circuit can be simplified.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a conventional optical receiver circuit, Fig. 2 is a diagram showing an outline of the configuration of an embodiment of the present invention, and Fig. 3 is a diagram showing an outline of the configuration of an embodiment of the present invention.
The figure is a diagram showing details of the configuration of the circuit according to the present invention shown in FIG. 2. Explanation of symbols = 11 is APD, 12 is amplifier circuit. 13 is a constant current power supply, 21 is an APD, 22 is a signal amplification circuit, 23 and 24 are DC amplification circuits, 25 is a DC/DC conversion circuit, and 26 is a resistor.

Claims (1)

[Claims] In an optical relay transmission line using a DC balanced transmission line code, an avalanche photodiode that converts an optical pulse train into an electric pulse train, and a constant current source that reverses the avalanche photodiode. An optical receiving circuit 0 characterized by comprising: