A 2.7 V CMOS dual-mode baseband filter for GSM and WCDMA

A 5th order analog CMOS continuous-time baseband filter for a dual-mode cellular phone was designed with maximum component sharing in the two modes. The filter was designed to meet the bandwidth requirements of both GSM and WCDMA standards. The area was minimized by using common capacitance matrices and operational amplifiers in the two modes. Operational amplifiers with a programmable GBW were used in order to minimize the power consumption in GSM-mode. The real pole of both fifth order transfer functions was realized as a passive integrated structure and a ladder filter was used to realize the two remaining complex pole pairs. This helped to reduce the power consumption further while resulting in a very low input referred noise. A 7-step gain tuning was implemented with tunable transconductance stage between the passive RC-loop and the active ladder structure. The measured frequency responses are in good agreement with simulations. The measured integrated input referred noise was 6.9 μV and 13.6 μV in the GSM- and WCDMA-modes, respectively. The IIP3 was +25 dBV in the WCDMA-mode and the circuit consumed 13.0 mW and 21.8 mW in the GSM- and WCDMA-modes, respectively