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

An 5th order analog CMOS RC-opamp baseband filter for a dual-mode cellular phone receiver was designed with maximum component sharing in the two modes. The filter meets the bandwidth specifications of both the PDC and WCDMA standards, which represent the two extremes in respect of the channel bandwith. The total area was minimized by reducing the filter order from five to three in the PDC-mode. Also, the operational amplifiers with adjustable GBW were used to minimize PDC-mode power consumption. The capacitance matrices were made only partially overlapping to reduce the resistance spread. The largest resistors were implemented with T networks and the smallest capacitors with series connections to extend the range of feasible passive component values. The measured frequency responses match the simulations very closely. The measured integrated input referred noise was 17 and 47uV in the PDC- and WCDMA-modes, respectively. The IIP3 was +35dBV in the WCDMA-mode and the circuit consumed 6.8mW and 25.4mW in the PDC- and WCDMA-modes, respectively.