Separation of close sinusoids by cross-coupled phase locked loop

A study is made of a cross-coupled phase-locked loop (CCPLL) used for separation of close sinusoids with slowly varying frequencies. It is assumed that the sinusoids have equal amplitudes, and it is shown that the CCPLL system can effectively separate two sine signals with an observation interval T<1/Δf. An analysis in the presence of noise is also given. It is shown that a satisfactory phase estimation can be achieved for SNR ⩾15 dB. The result has application in fields such as ranging, symbol synchronization, and carrier recovery for coherent demodulation