JPS62283710A - Light receiving circuit - Google Patents

Abstract

PURPOSE:To realize a complicated non-linear input/output characteristic, which is extremely difficult by an analog circuit, and to execute control with a high accuracy, by providing an A/D converting circuit, a digital processing circuit, and a D/A converting circuit, and generating various control signals at a stage of a digital signal. CONSTITUTION:A digital AGC control signal which has been generated by a digital processing circuit 7 is converted to an analog signal of the correspondent level a D/A converting circuit 8, and thereafter, supplied to a control signal input terminal of an AGC amplifying circuit 3, and controls a gain of this AGC amplifying circuit 3. Also, a digital bias control signal which has been generated by the digital processing circuit 7 is converted to an analog signal of the corresponding level in a D/A converting circuit 9, and thereafter, supplied to a control signal input terminal of a variable bias applying circuit 13, and a bias value of an optical/electric converting element 1 is controlled.Also, a digital reference voltage which has been generated by the digital processor 7 is converted to an analog signal of the corresponding level in a D/A converting circuit 10, and thereafter, supplied to a reference voltage input terminal of a discriminating/reprodecing circuit 4, and its discriminating/reproducing characteristic is controlled.

Description

3. Detailed Description of the Invention Object of the Invention Industrial Application Field The present invention relates to an optical receiving circuit used in an optical communication system, and particularly relates to an AGC circuit in which digital adjustment control is performed. It is something.

2. Description of the Related Art A typical optical receiving circuit installed in an optical communication system is configured as shown in FIG. In this optical receiving circuit, a received optical signal is converted into an electrical signal of a level corresponding to the received light level by an optical/electrical conversion element 1, amplified by a preamplifier circuit 2 and an AGC amplifier circuit 3, and then sent to an identification/regeneration circuit 4. Supplied. In parallel with this, the peak value of the output of the AGC amplifier circuit 3 is detected by the peak detection circuit 5, and the peak value of the output of the AGC amplifier circuit 3 is detected by the peak detection circuit 5.
The signal is supplied to the gain control signal input terminal of the AGC amplifier circuit 3 via the feedback circuit 11, and its gain is controlled. Further, the output of the peak detection circuit 5 is supplied to a bias control terminal of a variable bias application circuit 13 via a bias feedback circuit 12, and the bias value applied to the photo/electrical conversion element 1 is controlled from there.

As a result, the output amplitude of the AGC amplifier circuit 3 is stabilized, and this stabilized output is compared with a reference voltage of a predetermined value in the identification circuit 4, thereby performing stable identification and reproduction.

Problems to be Solved by the Invention In the conventional optical receiving circuit described above, in order to absorb variations in element constants and assembly work, the characteristics of the AGC feedback circuit 11 and the bias feedback circuit 12 and the reference voltage of the identification/circuit are However, in order to realize complex nonlinear input/output characteristics, a large number of variable constant elements must be combined.
Not only does the individual adjustment become complicated, but also the adjustment at one location affects the adjustment at other locations, resulting in a problem in that the accuracy of the adjustment decreases and the overall adjustment work becomes extremely complicated.

Configuration of the Invention Means for Solving the Problems The optical receiving circuit of the present invention includes an optical/electrical conversion element that converts an optical signal into an electrical signal, a variable bias application circuit that applies a variable bias voltage to the electrical conversion element, A preamplifier circuit that amplifies the output of the photo/electric conversion element, an AGC amplifier circuit that amplifies the output of this preamplifier circuit, an identification/regeneration circuit that identifies and reproduces the output of this AGC amplifier circuit, and an output of the AGC amplifier circuit. a peak detection circuit that detects the peak value of the peak detection circuit; an A/D conversion circuit that converts the output of this peak detection circuit into a digital signal;
a digital processing circuit that creates a third digital control signal; a first D/A converter that converts the first digital control signal of this digital processing circuit into an analog signal and supplies it to the gain control signal input terminal of the AGC amplifier circuit; a second D/C circuit that converts the second digital control signal into an analog signal and supplies it to a control signal input terminal of the variable bias application circuit;
The digital processing circuit is equipped with an A conversion circuit and a third D/A converter that converts the third digital control signal into an analog signal and supplies it to the reference voltage input terminal of the identification/regeneration circuit. It is designed so that it can be carried out freely and easily.

Hereinafter, the operation of the present invention will be explained in detail together with examples.

Embodiment FIG. 1 is a block diagram showing the configuration of an optical receiving circuit according to an embodiment of the present invention.

In Figure 1, 1 is a photo/electrical conversion element, 2 is a preamplifier circuit, and 3
is an AGC amplifier circuit, 4 is an identification/regeneration circuit, 5 is a peak detection circuit, 6 is an A/D conversion circuit, 7 is a digital processing circuit, 8, 9.10 is a D/A conversion circuit, and 13 is a variable bias application circuit. It is.

In this optical receiving circuit, a received optical signal is converted into an electrical signal of a level corresponding to the received light level by an optical/electrical conversion element 1, amplified by a preamplifier circuit 2 and an AGC amplifier circuit 3, and then an identification/regeneration circuit. 4.

In parallel with this, the peak value of the output of the AGC amplifier circuit 3 is detected by the peak detection circuit 5, converted into a corresponding digital signal by the A/D conversion circuit 6, and then supplied to the digital processing circuit 7. .

The digital processing circuit 7 processes the supplied digital peak value according to a built-in program, and generates a digital A c c I control signal for controlling the AGC amplifier circuit 3 and a digital A c c I control signal for controlling the variable bias application circuit 13 . - Create a bias control signal and a digital reference voltage to be supplied to the identification/regeneration circuit 4.

The digital AGC control signal created by the digital processing circuit 7 is converted into an analog signal of a corresponding level by the D/A conversion circuit 8, and then supplied to the control signal input terminal of the AGC amplifier circuit 3. Control the gain of 3. Further, the digital bias control signal created by the digital processing circuit 7 is converted into an analog signal of a corresponding level by the D/A conversion circuit 9, and then
The signal is supplied to the control signal input terminal of the variable bias application circuit 13, thereby controlling the bias value of the photo/electrical conversion element 1. Further, the digital reference voltage created by the digital processing device 7 is converted into an analog signal of a corresponding level in the D/A conversion circuit 10, and then supplied to the reference voltage input terminal of the identification/reproduction circuit 4, and the identification・Control playback characteristics.

Effects of the Invention As explained in detail above, the optical receiving circuit of the present invention has A
It is equipped with a /D conversion circuit, a digital processing circuit, and a D/A conversion circuit, and is configured to create various control signals at the digital signal stage, so it realizes complex nonlinear input/output characteristics that are extremely difficult to achieve with analog circuits. This enables highly accurate control.

In addition, since the digital processing device is configured to centrally create three types of control signals: the AGC feedback system, the bias feedback system, and the identification/reproduction system, the control of each system can be executed while maintaining mutual coordination. This makes it possible to achieve highly accurate control.

In particular, if a program is given to the digital processing circuit that uses the element constants of the main components of the optical receiver circuit as parameters, adjustment can be completed immediately by simply inputting data of the actual element constants for each circuit, and the adjustment process can be completed quickly. It can also be substantially reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical receiving circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional optical receiving circuit. l...Photo/electric conversion element, 2...Preamplifier circuit, 3...A
GC amplifier circuit, 4...Identification/regeneration circuit, 5...Peak detection circuit, 6...A/D conversion circuit, 7...Digital processing circuit, 8,9.10...D/A conversion circuit, 13.・Variable bias application circuit.

Claims (1)

[Claims] an optical/electrical conversion element that converts a received optical signal into an electrical signal; a variable bias application circuit that applies a variable bias to the optical/electrical conversion element; a preamplifier circuit that amplifies the output of the optical/electrical conversion element; an AGC amplifier circuit that amplifies the output of the amplifier circuit; an identification/regeneration circuit that identifies and reproduces the output of the AGC amplifier circuit; a peak detection circuit that detects the peak value of the output of the AGC amplifier circuit; and an output of the peak detection circuit. an A/D conversion circuit that converts the output into a digital signal; a digital processing circuit that processes the output of this A/D conversion circuit to create first, second, and third digital control signals; a first D/A conversion circuit that converts the first digital control signal into an analog signal and supplies it to the gain control signal input terminal of the AGC amplifier circuit; a second D/A conversion circuit that supplies the control signal input terminal of the application circuit; and a third D/A conversion circuit that converts the digital control signal into an analog signal and supplies it to the reference voltage input terminal of the identification/reproduction circuit. An optical receiving circuit characterized by comprising an A converter.