Automatic gain control circuit of trans-impedance amplifier

Abstract

The invention discloses an automatic gain control circuit of a trans-impedance amplifier. The automatic gain control circuit of the trans-impedance amplifier comprises a trans-impedance amplifier TIA1, a trans-impedance amplifier TIA2, a NMOS tube Q1, a NMOS tube Q2, an error amplifier U3 and a bias current source Ib; the input end of the trans-impedance amplifier TIA1 is connected with a drain electrode of the NMOS tube Q1; the output end of the trans-impedance amplifier TIA1 is connected with a source electrode of the NMOS tube Q1; the input end of the trans-impedance amplifier TIA2 is connected with a drain electrode of the NMOS tube Q2; the output end of the trans-impedance amplifier TIA2 is connected with a source electrode of the NMOS tube Q2; the in-phase input end and an inverted phase input end of the error amplifier U2 are respectively connected with the input end and output end of the trans-impedance amplifier TIA2; the output end of the error amplifier U2 is connected withgrid electrodes of the NMOS tube Q1 and the NMOS tube Q2; and the output end of the bias current source Ib is connected with the in-phase input end of the error amplifier U2 and the drain electrode ofthe NMOS tube Q2. The fast response of the automatic gain control of the trans-impedance amplifier TIA1 can be realized by the NMOS tube Q1 and the NMOS tube Q through adopting a device with low-starting voltage threshold.

Description

technical field [0001] The invention relates to the field of transimpedance amplifiers, in particular to an automatic gain control circuit for transimpedance amplifiers. Background technique [0002] In modern high-speed optical fiber communication systems, the transimpedance amplifier TIA (Trans-Impedance Amplifier) ​​plays the role of converting and amplifying the weak photocurrent signal generated by the photodiode into a voltage signal, and outputting it to the subsequent circuit for processing. Therefore, TIA is at the forefront of the receiving end and is the core device of the receiving end of the optical communication system. Its core indicators such as noise, sensitivity, dynamic range, and sensitivity basically determine the performance of the entire receiving system. [0003] The input dynamic range is an important indicator in the transimpedance amplifier circuit, which is defined as the difference between the saturated input optical power and the sensitivity. S...

AI Technical Summary

Problems solved by technology

But this method has a disadvantage. The threshold of the typical diode’s turn-on voltage is about 0.7V, and the threshold of the turn-on voltage of the diode-connected MOS tube is basically above 0.4V; and the general transimpedance amplifier TIA The output amplitude will not produce obvious distortion only within 0.2V. Therefore, the general voltage-controlled shunt element can only use a special low threshold (low threshold) device to realize the fast response of the automatic gain control of the transimpedance amplifier. The price is that the process cost increases and special process support is required. Many commercial processes do not support the process options of this special device.

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