A feed-forward AGC circuit with 48 dB-gain range, 1.2 μs minimum settling time for WiMAX receiver

Abstract

The IEEE 802.16 standard uses orthogonal frequency division multiplexing (OFDM) to allow high data rates in WiMAX environment. The stringent settling-time constraints of OFDM signals make conventional closed-loop feedback AGC impractical for WiMAX applications. This paper presents a novel fast-settling feed-forward automatic gain control (AGC) circuit designed for WiMAX receivers. The proposed AGC uses a switched coarse gain-setting followed by a continuous fine gain-setting to accelerate locking speed. The coarse gain-setting is performed without peak detection (PD) and the fine gain-setting is carried out by a one-step method both for shortened settling time. The chip is fabricated in 0.13 μm CMOS technology. The measurement results verify that the 48 dB AGC converges to the desired level within 1.2 μs minimum settling time. Besides, the THD is 0.32---1.37 % and the power consumption is 5.2 mW accordingly.