A Digital Phase Locked Loop based Signal and Symbol Recovery System for Wireless Channel by Basab Bijoy Purkayastha & Kandarpa Kumar Sarma

Author:Basab Bijoy Purkayastha & Kandarpa Kumar Sarma
Language: eng
Format: epub
Publisher: Springer India, New Delhi

Fig. 5.10Nyquist rate phase detector

Fig. 5.11Nyquist rate phase detector waveform

5.6.3 Nyquist Rate (NR) Phase Detector

A very common and easy to implement PD is the Nyquist rate PD (NRPD). The DPLL based on NRPD was proposed in [5, 6] and subsequently developed by the works in [7–9]. As depicted in Fig. 5.10 the NRPD is basically a digital multiplier. The incoming signal is band pass filtered to ensure that high frequency components that would cause aliasing are not allowed into the system. Often this type of filter is called an anti-aliasing filter. Filtered signal is then sampled uniformly at the Nyquist rate and converted to bit digital signal by an analog-to-digital converter (ADC). The digital phase difference signal is obtained by multiplying the numerically controlled oscillator (NCO) local reference signal with the signal out of ADC. The waveforms for the NRPD (Fig. 5.11) show that the incoming signal is sampled according to the clock pulses. The output from the digital multiplier or the phase difference signal is shown to contain an average value. As depicted in the figure, this average value is not zero and causes the signal not to be centered on the horizontal axis. This average value is filtered out by the next stage in the DPLL, the digital loop filter.

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