Dual-mode bluetooth/wireless local area network channel-select filter for direct conversion receivers

System level analysis is used to extract various specifications of the channel select filter for integrated dual-mode CMOS bluetooth (BT)/wireless local area network (WLAN; IEEE 802.11b) receivers. A digitally programmable active-RC filter suitable for direct conversion topology is presented. Six-bit R-2R ladders are used to adjust the filter bandwidth with tuning resolution better than 1.56%. Experimental results obtained from 0.35 μm CMOS chips show that using a fourth-order filter satisfies the selectivity requirements of both applications. The filter exhibits spurious free dynamic range of 70.6 and 61.2 dB for BT and WLAN, respectively.