JPH03249811A - Light-receiving amplifier - Google Patents

Abstract

PURPOSE:To set a DC offset constant in spite of an AGC control error by independently providing a circuit controlling the DC offset of an output and an AGO control circuit setting amplitude constant. CONSTITUTION:The DC offset control circuit and the AGC offset circuit are independently provided. A DC feedback circuit 8 feeds back the peak holding values of a positive phase SD and the negative phase SD so that they are kept constant. Thus, the DC offset becomes constant in spite of output amplitude being the AGC control error. Thus, a light-receiving amplifier where the DC offset is not shifted even if there is the AGC control error can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light receiving amplifier equipped with a qDC offset control circuit and a 5Gc control circuit.

[Conventional technology]

Figure 8 shows a conventional general C offset control circuit and an AG
FIG. 2 is a circuit diagram of a light receiving amplifier equipped with an O control circuit.

In the figure, Ill is a light receiving element, and 1!1 is a light receiving element 11.
1 is a preamplifier that converts current into voltage, 13I is an automatic gain control circuit (hereinafter referred to as AGO amplifier), (8D) H positive phase output, CBD) is a negative phase output, (41 is a positive phase peak hold circuit, fat Fi Reverse phase peak hold [OL path,
(61 is a positive phase and negative phase intermediate value detection circuit, 171 is an AGO feedback circuit that applies feedback to keep the difference between the positive phase peak hold 141 and the positive phase and negative phase intermediate value detection circuit (6) constant, (8) is a DC feedback circuit that applies feedback to keep the difference between the negative phase peak hold +Il and the positive phase and negative phase intermediate value detection circuit 161 constant.

Next, the operation will be explained.

The electric current of the photodetector III is converted into a voltage by the Rt preamplifier +71, amplified by the AGO amplifier; The positive phase and negative phase intermediate value detection circuit 16) detects the intermediate value between the positive phase and the negative phase. The Go feedback circuit (
71, it is fed back to the AGO amplifier iml. In addition, the AG is controlled by the DC feed puncture circuit (8) so that the difference between the negative phase peak hold value and the intermediate value detection value is constant.
It is fed back to the O amplifier 13. These two feedbacks control the output amplitude DC offset to be constant.

[Problem to be solved by the invention]

Since the conventional DCC off-celler and the light receiving amplifier equipped with the AGo11111 circuit were configured as described above, the AGC
If there is an error in the output amplitude, which is a control error, the DC offset control circuit will work to keep the difference between the negative phase peak hold value and the intermediate detection value constant, as shown in the output waveform diagram shown in Figure wi4, and the DC offset will shift. There was a problem with this.

This invention was made to solve the above-mentioned problems, and aims to provide a light receiving amplifier in which the DD offset does not shift even if there is a Go control error.

[Means to solve the problem]

The light receiving amplifier according to the present invention has an independent DC offset control circuit and a Go offset circuit.

[Effect]

In the light receiving amplification WA in this invention, the DC offset control circuit and the AGO control circuit are made independent, so that the DC offset is constant regardless of the AGO control error.

[Implementation row]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a light receiving amplifier which is an embodiment of the present invention. In the figure, (h) is a DC feedback circuit,
Feedback is applied to keep the peak hold values of the positive phase and negative phase constant.

In the drawings, the same reference numerals as in the prior art design indicate the same or corresponding parts, and the explanation thereof will be omitted.

Next, the operation will be explained.

Since the DC feedback circuit (8) is set to a feed balance so that the difference between the peak hold values of the positive phase and negative phase is constant, the A()0111J# error is related to the output amplitude as shown in Figure 2. According to the invention, as described above, since the DC offset control circuit and the Go control circuit are made independent, the DC offset remains constant regardless of the AGO control error. Moreover, there is an effect that feedback adjustment becomes easier.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a light receiving amplifier according to an embodiment of the present invention, [Figure 1 is an output waveform diagram of the light receiving amplifier shown in Figure 1, Figure 3 is a circuit diagram of a conventional light receiving amplifier, and Figure 1 is a circuit diagram of a light receiving amplifier according to an embodiment of the present invention. Third
It is an output waveform diagram of the figure. In the figure, 1llFi light receiving element, (!1 is preamplifier, 13) is AGO7/pu, +41. l! il is a peak hold circuit, 1g1 intermediate value detection circuit, It) Fi
The feedback circuit 181FiDc shows the feedback path. In addition, in the figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A light-receiving amplifier characterized by independently comprising a circuit for controlling the DC offset of the output and an AGO control circuit for keeping the amplitude constant.