Abstract: A complex digital sampling converter, for use with an IF demodulator, includes: an analog-to-digital converter (ADC) receiving the IF analog signal for conversion to a digital data stream by sampling at a sampling rate frequency substantially equal to four times the IF signal frequency; a digital mixer for converting the sampled data to baseband; a sorter for separating the interleaved sequential in-phase I data words and quadrature-phase Q data words into a pair of concurrent I and Q data word streams; and at least one of a circuit for removing the effects of any DC offset in the analog IF signal applied to the ADC, and a circuit for correcting misalignment errors in the concurrent I and Q streams.

Abstract: A variable-delay, sine-cosine non-coherent demodulator recovers digital data angle-modulated upon a radio-frequency (RF) carrier signal, by frequency conversion of the carrier signal to a selected IF frequency, which is ideally equal to one-fourth of a sample frequency supplied to the demodulator. The IF signal is sampled at the sample frequency, and the samples are then sorted to provide a pair of baseband quadrature-phased I and Q signals. Each of the I and Q signals is delayed by a variable first delay T.sub.1 to provide first-delayed in-phase I.sub.1 and first-delayed quadrature-phased Q.sub.1 signals. These signals are then delayed by a second delay T.sub.2 to provide twice-delayed in-phase I.sub.2 and twice-delay quadrature-phase Q.sub.2 signals. The sum of the two delays is a constant related to the sample frequency, which itself is related to the data bit rate, but the first delay T.sub.1 is variably dependent upon the frequency offset between the IF signal and the sample signal.