A dual-mode low-pass filter for 802.11b/Bluetooth receiver

The design of a dual-mode low-pass channel selection filter for a dual-standard 802.11b/Bluetooth direct conversion receiver is presented. The filter is an OTA-C, 5/sup th/ order, Butterworth low pass structure. The OTA is implemented as a source-degenerated bipolar differential pair. Dual-mode operation, 600 kHz cut-off frequency for Bluetooth mode and 6 MHz for Wi-Fi mode, is achieved by switching the source-degeneration resistors and the capacitors. The filter operates from a single 2.5 V supply while consuming 2.7 mA and 0.9 mA for 802.11b and Bluetooth, respectively. It achieves 10 dBm in-band IIP3, 40 dBm out-of-band IIIP3 for both modes. The measured input referred noise density is -148.92 dBV/Hz and -140.48 dBV/Hz for 802.11b and Bluetooth, respectively.