Abstract: This paper presents a programmable gain amplifier (PGA) circuit with a digitally assisted DC offset cancellation (DCOC) scheme for a direct conversion WLAN receiver. Implemented in a standard 0.13-μm CMOS process, the PGA occupies 0.39 mm² die area and dissipates 6.5 mW power from a 1.2 V power supply. By using a single loop single digital-to-analog converter (DAC) mixed signal DC offset cancellation topology, the minimum DCOC settling time achieved is as short as 1.6 μs with the PGA gain ranging from -8 to 54 dB in a 2 dB step. The DCOC loop utilizes a segmented DAC structure to lower the design complexity without sacrificing accuracy and a digital control algorithm to dynamically set the DCOC loop to fast or normal response mode, making the PGA circuit in compliance with the targeted WLAN specifications.

Key words: direct conversion receiver