Performance of a quadricorrelator driven by modulated signals

An analysis is presented of a balanced quadricorrelator driven by a digital-modulated signal with thermal noise. The aim is to assess its performance as a frequency difference detector. The circuit output is decomposed into a signal term and a disturbance referred to as noise. Exprssions are given for the signal and for the power spectral density of the noise as a function of the various system parameters. Design criteria are provided to minimize the output noise for zero frequency offset. In particular, it is found that at high signal-to-noise ratios the noise level can be made vanishingly small by the proper choice of the quadricorrelator filters. A similar result has been recently discovered for another frequency difference detector, the dual-filter detector. It is shown that a balanced quadricorrelator and a dual-filter detector can be made totally equivalent