Charge-domain FIR sampler with programmable filtering coefficients

A charge-domain sampling technique for integrating an arbitrary FIR filtering function into high-frequency signal sampling is presented. The impulse response of the sampler´s built-in FIR filtering function is implemented by weighting signal current samples integrated into a sampling capacitor with a discrete-time current multiplier unit, which is constructed from sets of parallel current-mode switches, each carrying a unit current element. The fine achievable resolution and digital controllability of the multiplier values, and hence the filter tap coefficients, allows realization of advanced programmable mixed-mode FIR filtering functions. Circuit simulation results of an example 50-MHz IF-sampler with a built-in 22-tap complex bandpass sinc³ FIR function in 0.35-μm CMOS are shown, demonstrating the feasibility of the presented method.