A 2.4–2.5 GHz WLAN Direct-Conversion Receiver Front-End With Low-Distortion Baseband Filters

Low-distortion I/Q baseband filters interface with a 2.5 GHz RF receiver front-end configured as a Gm-cell in a direct-conversion architecture targeted towards WLAN 802.11b application. The active I/Q current-mode filters use AC current to carry the large swing of both desired and blocker signals, relaxing the voltage headroom requirement to a 1.2 V supply. An on chip master-slave automatic tuner is used to lock the filter bandwidth to a precision 20 MHz reference crystal oscillator, resulting in a <3% tuning accuracy and <0.5% I/Q bandwidth matching. The receiver achieves a 3.2 dB DSB NF, -14 dBm out-of-band IIP3, and + 27 dBm worst case IIP2, all referred to the LNA input, while drawing 30 mA from a 2.7 V supply. The chip is fabricated in a 0.5 mum 46 GHz f_T SiGe BiCMOS process. The active area is 2.54 mm².