COMPLEX PHASE-LOCKED LOOP DEMODULATOR FOR LOW-IF AND ZERO-IFRADIO RECEIVERS

摘要

A digital demodulator which coherently demodulates a low-IF or zero-IF compl ex signal using a complex-valued phase-locked loop (CPPL). The CPPL includes a numerical controlled oscillator, four multipliers and two combiners to provi de independent phase/frequency and amplitude outputs. The CPLL exhibits in firs t order PLL dynamics without a loop filter in the feedback loop to the NCO. However a filter with one or more poles may be included in the feedback circuit to exhibit 2 nd or higher order PLL dynamics. The CPLL allows coherent demodulation of extremely low F M modulation indexes whereby the incoming frequency drift may be larger than t he frequency deviation. It can also be used to coherently demodulate signals which have combined amplitude and phase characteristics.