A Synchronous Sweep Frequency Oscillator

This paper describes a linear frequency sweep oscillator which is accurately controlled by a master clock. The voltage controlled oscillator which generates the frequency sweep is first phase-locked to the master clock. Then, a ramp generator drives the voltage controlled oscillator over the required frequency range, while a phase-sampling loop controls the instantaneous frequency to the desired ramp accuracy. The phase-sampling control loop is synchronized to the master oscillator by the sampling rate, which is derived directly from the master clock frequency. A laboratory system constructed on these principles sweeps from 2.095 MHz to 2.320 MHz in approximately 1.709 seconds, with a deviation from linearity of less than ±75 Hz.