Serially_programmable_VHF_frequency_synthesizer_1

Published:2009/7/23 22:34:00 Author:Jessie | From:SeekIC

This circuit uses an NJ8822 single-chip synthesizer, an SP8793 dual-modulus prescaler, and an SL562 low-noise op amp to form a frequency synthesizer, with an output range from 144 to 146 MHz at a level of +3 dBm into 50Ω. The lock-up time for a 1-MHz change in frequency is 80 ms. The NJ8822 is programmed via a serial microprocessor interface. The VCO (using a coax resonator) is modulated by applying audio to the cathode of a reverse-biased PIN diode. The loop filter uses the SL562, which has a loop bandwidth of 60 Hz (with the values shown) and a damping factor of 0.6. The filter is followed by a low-pass pole at 3.7 kHz to attenuate the 12.5-kHz reference sidebands.



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