A frequency-shifting technique is discussed that uses a digital filter
to interpolate a bandpass-sampled signal at a low-pass position. The
discussion focuses on the derivation of the required digital filter. I
t is shown that second-order bandpass sampling offers more flexibility
than first-order bandpass sampling. It is also shown how well-known q
uadrature-sampling methods for frequency-shifting are special cases of
the general second-order sampling technique.