A compact digitally programmable reconfigurable filter for dual-mode BT/802.11b receivers

A new 4th-order reconfigurable (complex bandpass or normal lowpass) filter for implementing the channel select filter for dual-mode receivers adopting low-IF for Bluetooth (BT) and zero-IF for WLAN (IEEE 802.11b) is presented. It provides an alternative solution to the optimum low-power complex filter based on the current amplifier. The new filter avoids the employment of capacitor and/or resistor banks leading to an area efficient design solution while maintaining high linearity and relatively low power consumption. The center frequency in BT mode and the pole frequency in 802.11b mode are digitally tuned through programming active current division networks (CDNs). Experimental results obtained from 0.18 μm CMOS chips show that the proposed design offers improved characteristics over available solutions in terms of power consumption, spurious-free dynamic range (SFDR) and/or area. It achieves in-band SFDR of 65.3 dB for BT and 65.2 dB for 802.11b while it consumes 1.8 mW. Also, it offers image rejection of better than 59 dB.