Fuzzy controlled phase locked loop (FCPLL)

Abstract

Phase locked loop (PLL) operates on the principle of feed back control, except that the feed back quantity is not the amplitude but the phase of the sinusoidal input signal. If the input sinusoid is noisy, the PLL not only tracks the sinusoidal signal, but also cleans it up. The PLL can be used as an FM demodulator and frequency synthesizer. The PLL, being a relatively inexpensive integrated circuit, has become one of the most frequently used communication circuit. PLL is also used in space-vehicle-to-earth data links where there is a premium on transmitter weight or where the loss along the transmission path is very large. A classic PLL consists of a voltage controlled oscillator (VCO), a multiplier serving as a phase detector (PD) or phase comparator and a loop filter. The VCO adjusts its own frequency until it is equal to that of the input sinusoidal signal such that the frequency and phase of the two signals are in synchronism (except for a possible difference of a constant phase). This paper deals with some aspects of design and analysis of Fuzzy-Controlled PLL. It considers control of the loop gain by studying the phase variation between the two signals. The fuzzification deals with triangular membership functions for phase angle of the input signal and the voltage Vdc of the output signal. Fuzzy inference is drawn using IF-THEN rules. Defuzzification is carried out using height defuzzification method. We report improvement in S/N ratio and the lock in range frequency of a fuzzy controlled PLL as compared with that of classic PLL. © 2003 Taylor & Francis Group, LLC.