Analog-input digital phase-locked loops for precise frequency andphase demodulation

摘要

Most conventional analog-input digital phase-locked loopsn(ADPLL's) suffer from the effect of in-loop quantization and fromnnonlinear behavior caused by the approximations inherent in practicalndigitally controlled oscillators (DCO's). The resulting errors limit thenaccuracy of ADPLL-based frequency demodulation and usually makenADPLL-based phase demodulation impractical because of severe phase-driftnproblems. This paper presents a new class of ADPLL's that areninsensitive to the deleterious effects of quantization, and do notnexhibit nonlinear behavior when implemented with practical DCO's. ThenADPLL's are well suited to applications requiring precise frequencyndemodulation, and can also be used for phase demodulation because theirnquantization error is well behaved even after discrete-time integration.nThe paper establishes an analogy between the ADPLL's and delta-sigmanmodulators, and applies existing delta-sigma modulator results tonpredict the frequency and phase demodulation accuracy of the ADPLL's. Anmechanization of the general architecture consisting of easilynimplemented components such as analog integrators, digital flip-flops,nand digital counters is then presented and analyzed