A Transimpedance Amplifying Circuit Capable of Realizing Automatic Gain Control

Abstract

A transimpedance amplifying circuit capable of realizing automatic gain control comprises: a transimpedance amplifying front-end circuit, a phase splitting circuit and an AGC feedback network. The transimpedance amplification front-end circuit converts the input current signal into a voltage signal, including a first switch tube, a second switch tube and a first MOS tube; the collector of the first switch tube is connected to the base of the second switch tube; The base of the first switch tube is connected to the emitter of the second switch tube through transresistance; the source of the first MOS tube is connected to the base of the first switch tube, and the drain of the first MOS tube (M0) The pole is connected to the collector of the first switching tube; the AGC feedback network includes a peak detection circuit and a comparison circuit; the peak detection circuit detects the differential voltage signal output from the phase-splitting circuit, and outputs a DC voltage; the comparison circuit detects the peak detection circuit The output DC voltage is compared with the reference level; the output end of the comparison circuit is connected to the gate of the first MOS transistor.

Description

technical field [0001] The invention relates to a transimpedance amplifying circuit, in particular to a transimpedance amplifying circuit capable of realizing automatic gain control. Background technique [0002] A transimpedance amplifier is an electronic circuit that converts a current signal into a voltage signal and amplifies it. It is often used as the front-end circuit of an optical communication receiving chip. The transimpedance amplifier circuit needs to have a large enough input dynamic range to meet the application. In order to ensure that the transimpedance amplifier circuit can handle large signals, it is necessary to introduce an automatic gain control mechanism in the transimpedance amplifier circuit, that is, when the input signal is greater than a certain value, the circuit The automatic gain loop starts to work, reducing the gain of the transimpedance amplifier circuit, so as to achieve the function of processing large signal input. [0003] There are main...

AI Technical Summary

Problems solved by technology

This structure has a disadvantage: when the automatic gain loop starts to work, the dominant pole of the loop moves to high frequency due to the reduction of transimpedance, and the stability margin decreases because the loop gain does not change, and the signal processing will be degraded. Ringing occurs, so large input dynamics cannot be met

[0007] These two shortcomings create two insurmountable problems

[0008] 1. When the automatic gain control loop is turned on and Vcon is small, the bandwidth of the transimpedance amplifier circuit may not be large enough to handle high-speed signals due to the sudden decrease of the loop gain

[0009] 2. When the automatic gain control loop is turned on and Vcon exceeds a certain value, since the loop gain cannot continue to decrease, the stability margin of the loop may be insufficient, and ringing will occur after signal processing

Images