A charge sampling mixer with embedded filter function for wireless applications

A charge sampling mixer with embedded and programmable filter function is described, which is not based on the conventional sub-sampling but the proposed bandpass charge sampling (BPCS) principle. A BPCS circuit samples a radio signal by integrating the weighted current of the clocked radio signal in n clock cycles. The large sampling capacitor used in the circuit results in low noise and low charge and clock feedthrough. The BPCS circuit is simultaneously a high-Q filter, a homodyne mixer and a baseband signal sampler. The center frequency, the bandwidth and the adjacent selectivity can be set through the clock frequency, the number n and the weighting function. Simulation results of a 4 GHz charge sampling mixer in 0.35 μm CMOS are shown in the paper