Noise and False-Lock Performance of the PSK-Tanlock Loop

The tanlock modification of the phase detector characteristics of a phase-lock loop can be used to increase the linear range of operation of the S-curve of an analog loop, hence increasing the tracking and acquisition ranges without increasing the loop gain. The phase-shift-keying tanlock loop is a realization of this modification for the coherent demodulation and tracking of a PSK suppressed carrier signal. In this paper we consider the PSK-TLL loop performance in the presence of additive noise. The equivalent noise source used with the baseband model of the loop is derived. Both linear and quasi-linear approximations are considered for evaluation of the phase error variance (mean-square tracking error) of the loop. The false-lock performance of the PSK-TLL due to distortion of the digital data caused by the limited bandwidth of the arm filters is also considered. Results are obtained for both NRZ and Manchester encoded data symbols.