Abstract: An automatic gain control (AGC) circuit is implemented in UMC65 nm CMOS process for ultra-high frequency (UHF) radio frequency identification (RFID) reader receiver. The system consists of a variable gain amplifier (VGA), a peak detection circuit, a loop filter, a comparator and an exponential gain control circuit. The simulation results show that the gain of VGA varies linearly from 4 dB to 70 dB when the control voltage varies from 0.85 V to 0.35 V. The circuit has a constant -3 dB bandwidth of 10 MHz. For modulation depth 60% input AM signal with a modulation frequency 1 kHz, this AGC needs 20 μs to stabilize the output voltage. The final circuit consumes 6.6 mA current from a single 1.2 V voltage supply.