A charge-domain sampling technique for integrating an arbitrary FIR filtering function into high-frequency signal sampling is presented. In the method, 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 sin(c{sup}3) FIR function in 0.35-μm CMOS are shown, demonstrating the feasibility of the presented method.
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