Experimental 1-V flexible-IF CMOS analogue-baseband chain for IEEE 802.11a/b/g WLAN receivers

Abstract

A low-voltage low-power analogue-baseband chain designed for IEEE 802.11a/b/g wireless local-area network (WLAN) receivers is described. It features architecturally a ‘two-step channel selection’ to complement the radio front-end, and a flexible intermediate frequency (IF) reception capability to alleviate the cancellation of frequency and DC-offset. In circuit implementation, a double-quadrature downconverter based on a ‘series-switching’ mixer-quad realises a wideband-accurate I/Q demodulation. A ‘switched-current-resistor’ programmable-gain amplifier (PGA) minimises the bandwidth variation and transient in gain tuning by stabilising, concurrently, the PGA's feedback factor and quiescent-operating point. An ‘inside-OpAmp’ DC-offset canceller creates area-efficiently a very low cut-off frequency high-pass pole at DC while providing a fast settling of DC-offset transients. Fabricated in a 0.35 µm complementary metal-oxide semiconductor (CMOS) process without resorting to any specialised device, the prototype consumes 14 mW per channel at 1 V. The transient time in a 52-dB gain step is <1 µs and the stopband rejection ratio at 20/40 MHz is 32/90 dB. The error vector magnitudes are −27 and −17 dB for 802.11a/g and b modes, respectively.