An Automatic Gain Control Circuit for a Single-Chip UHF RFID Reader Transceiver

This paper presents an automatic gain control (AGC) circuit which is used in a single-chip UHF RFID reader transceiver system. The VGA is a fully differential circuit with differential output swing of 1-Vpp. The gain of the two VGAs can be varied linearly from 0dB to 60dB with respect to a control voltage from 0.28V to 0.93V. The exponential voltage to current (V-I) convertor is based on Taylor’s series expansion. The AGC circuit consumes 4.5mA current and has a 2.7MHz 3-dB bandwidth when the gain is 60dB. A differential positive peak detector is used in the AGC circuit loop. The AGC circuit is based on UMC 0.18-μm single-poly six-metal CMOS process technology.