SIMPLE_PLL_DEMODULATOR

Published:2009/7/16 2:11:00 Author:Jessie | From:SeekIC

Requires only single IC to provide synchronous detection. Performance is satisfactory for most requirements of most amateur radio experimenters. Gates A, B, and C in IC form relaxation-type VCO whose output frequency is determined by C1 and positive current sources supplying pins 10 and 13 of IC. When pin 6 is high, gate D is biased by R2 and R3 to operate as linear amplifier for input signal. In operation, pin 6 is made alternately high and low by oscillator output, so D acts as amplifying phase detector. Output goes through low-pass filter R4-C2 to VCO, completing phase-locked loop. Separate filter R5-C3 provides AF output. When C1 is 22 pF, circuit operates at about 10 MHz. With 270 ohms for R6, lock is maintained over range of 2 MHz; with 10 kilohms, locking range is 300 kHz. R7 is optional, for fine adjustment of frequency.-R. King, Phase-Locked Loop Demodulator, Wireless World, July 1973, p 337.



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