Digital complex sampling

Complex signal handling is employed in processing procedures in which the input signal is bandpass in origin and is to be processed in lowpass form. Normally, two-channel processing in quadrature channels is required to remove an ambiguity as to whether a signal is higher or lower than the bandpass center frequency. Complex signal processing has now been extended to the digital signal processing field. A conventional complex sampling scheme is shown. The scheme uses two quadrature analog channels and two A/D converters. This method has the disadvantage that two complete channels are required and that the channels must be very closely matched in phase and amplitude. These disadvantages may be overcome by using a digital complex sampling scheme employing one A/D converter. The advantages of the new technique over the conventional one are that no analog components apart from the A/D converter are required and that accurate phase and amplitude balance in the two channels are more easily achieved.