SPICE simulation of a sampler with anti-aliasing filter. According to the Shannon’s theorem, a signal must be sampled at a frequency greater than twice the highest frequency component in the analog signal for recovering the original waveform. Low-pass filtering prevents aliasing (extra frequency generated). A PCM sampling rate of 8Khz for example means a 4 kHz theoretical maximum input signal frequency. This circuit implements an anti-aliasing second-order Sallen and Key active low-pass filter preceding a dual sampling switch IC CD 4016.