AUTOMATIC GAIN CONTROL CIRCUIT OF TRANSIMPEDANCE AMPLIFIER

摘要

An automatic gain control circuit of a transimpedance amplifier, comprising a transimpedance amplifier TIA1 and a transimpedance amplifier TIA2, an NMOS transistor Q1, an NMOS transistor Q2, an error amplifier U3, and a bias current source Ib; an input end of the transimpedance amplifier TIA1 is connected to a drain electrode of the NMOS transistor Q1; an output end of the transimpedance amplifier TIA1 is connected to a source electrode of the NMOS transistor Q1; an input end of the transimpedance amplifier TIA2 is connected to a drain electrode of the NMOS transistor Q2; an output end of the transimpedance amplifier TIA2 is connected to a source electrode of the NMOS transistor Q2; a same-phase input end and an inverse-phase input end of the error amplifier U3 are respectively connected to the input end and the output end of the transimpedance amplifier TIA2; an output end of the error amplifier U3 is connected to a gate electrode of the NMOS transistor Q1 and a gate electrode of the NMOS transistor Q2; and an output end of the bias current source Ib is connected to the same-phase input end of the error amplifier U3 and a drain electrode of the NMOS transistor Q2. The NMOS transistor Q1 and the NMOS transistor Q2 can achieve a fast response of the automatic gain control of the transimpedance amplifier TIA1 without the need for a low turn-on voltage threshold device.