Digital complex sampling

Complex sampling is often employed in digital signal processing schemes where the input signal is bandpass in origin and is to be processed using lowpass techniques. Conventionally the signal is first mixed to zero centre frequency in two quadrature channels, filtered to remove the high-frequency mixing products and then digitised in two A/D convertors. A method is proposed that employs only one A/D convertor followed by digital mixing to produce the required pair of signals, thus allowing a considerable saving in hardware.