An improved double sampling scheme for switched-capacitor delta-sigma modulators

A switching scheme for a delta-sigma modulator (DSM) is described that allows double-sampled integrators to be used without degrading the performance of the DSM. To implement double sampling, two capacitors are required and it is impossible to assure perfect matching of these capacitors. With previously described switching methods, this capacitor mismatch causes a degradation in baseband signal-to-noise ratio. The novel switching scheme converts the capacitive mismatch into an additive out-of-band tone that has no impact on the performance of the DSM. Simulations have verified that, for arbitrary capacitor mismatches with an ideal op-amp, the improved double sampling scheme provides nearly perfect performance.<>