AGC (Automatic Gain Control) circuit for transimpedance amplifier

Abstract

The invention relates to an AGC (Automatic Gain Control) circuit for a transimpedance amplifier. An output voltage sampling module acquires an amplitude sampling signal and a common mode sampling signal from a differential output voltage signal; a threshold modulation module is used for removing a module high-frequency component from the common mode sampling signal and setting the threshold of the common mode sampling signal so that an output threshold modulation signal is different from the amplitude sampling signal to some extent; a low-frequency linear amplifier is used for identifying and amplifying the threshold modulation signal and the amplitude sampling signal; and an AGC signal output by the low-frequency linear amplifier is used for modulating the equivalent resistance of an MOS (Metal Oxide Semiconductor) transistor to control the gain of the transimpedance amplifier. The AGC circuit obtains an AGC control voltage by sampling, analyzing and processing output signals to realize stable output, moreover, since the variation range of the output signals is smaller, from tens of mV to hundreds of mV, and the span of the output signals is about 25dB, the grain of the transimpedance amplifier can be controlled linearly under input photoelectriccurrent in a large dynamic range.

Description

technical field [0001] The invention relates to an automatic gain control circuit, in particular to an AGC (Automatic Gain Control, automatic gain control) circuit for a transimpedance amplifier. In particular, it refers to the automatic gain control circuit used for cross-group amplifiers in optical receiving modules. Background technique [0002] In the field of optical communication, cross-group amplifiers are usually used as preamplifiers for receivers. Researchers at home and abroad have done a lot of research on transimpedance amplifiers. The AGC circuit used by the general transimpedance amplifier mainly samples the current of the input signal, and obtains the AGC control voltage by analyzing and processing the sampled current, thereby controlling the gain of the transimpedance amplifier, so that the output of the transimpedance amplifier remains constant; and because The change range of the input signal current is large, from uA level to mA level, and its span reac...

AI Technical Summary

Problems solved by technology

The AGC circuit used by the general transimpedance amplifier mainly samples the current of the input signal, and obtains the AGC control voltage by analyzing and processing the sampled current, thereby controlling the gain of the transimpedance amplifier, so that the output of the transimpedance amplifier remains constant; and because The input signal current has a large range of variation, from uA level to mA level, and its span reaches 50dB. Under such a large dynamic range input signal, it is difficult to linearly control the gain of the transimpedance amplifier.

Images