Fast Switching Synthesizer

The most common approaches used for achieving large step fast synthesizer switching is to pretune the VCO by a coarse tuning voltage produced by a D/A circuit, or by using switching inductors in the VCO. Both solutions suffer from poor noise immunity and much circuit hardware. This paper presents a new technique for increasing the switching speed of high resolution PLL synthesizers. A novel solution is presented whereby the Reference Frequency is increased for a short period of time so as to increase the natural frequency of the loop ¿n and thereby accelerating the loop´s acquisition time. After acquiring lock the Reference Frequency is changed back to its high resolution value. Experiments incorporating this technique were conducted with a 10-kHz step synthesizer that achieved a 1-msec lock-time for a 300 to 460 MHz change.