CHARACTERISTICS OF PHASE DETECTORS IN PRESENCE OF NOISE

Abstract

The phase detector is an important device used extensively in phase locked loops and in coherent detectors. Its characteristics must be known to predict the behaviour of the phase locked loop especially by non linear analysis. Noiseless analysis has been made for great varieties of phase detectors, but a satisfactory analysis in presence of noise is still needed. Many authors make the implicite assumption that the characteristics in presence of noise and without noise are alike, what is wrong. In fact it will be shown that all phase detector characteristics become sinusoidal at low signal to noise ratios whatever their noiseless characteristic may be. Besides, it will also be shown that when used as coherent detectors, sinusoidal phase detectors are better than linear phase detectors regarding the output signal to noise ratio, and output signal to noise spectral density ratio.