Gm-C complex transitional filter for low-IF wireless LAN application

The design and implementation of a gm-C complex filter for low-IF WLAN is described. Fifth-order transitional complex Bessel-Chebyshev filter is implemented to compromise between high attenuation and low group-delay variation. The circuit is fabricated using 0.18 /spl mu/m CMOS process. Measured results show that the filter provides 30 dB to 40 dB image rejection and 18 dB adjacent channel rejection, while keeping a low group-delay variation of below 6.0ns within the pass-band. High frequency and wide bandwidth filter also requires stringent design specification of the circuitries. Differential inverter transconductor is optimized for this gm-C continuous-time filter design. The complete filter including on-chip tuning circuit and bandgap consumes only 7.5 mA with 1.8 V single supply voltage.