PLL_WITH_DIVIDE_BY_N_CIRCUIT

Published:2009/7/13 21:37:00 Author:May | From:SeekIC

The MAX038 function generator IC can be used in a PLL system. To gain the advantages of a wider capture range and an optional divide-by-N circuit (which allows the PLL to lock onto arbitrary multiples of the applied frequency), you can introduce an external frequency-phase detector, such as the 74HC4046 or the discrete-gate version shown. Unlike phase detectors, which can lock to harmonics of the applied signal, the frequency-phase detector locks only to the fundamental. In the absence of an applied frequency, its output assumes a positive dc voltage (logic 1) that drives the RF output to the lower end of its range as determined by resistors R4 to R6. These resistors also determine the frequency range over which the PLL can achieve lock. Again, R4 to R6, C4, and RZ, determine the PLL's dynamic performance.



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