Method and circuitry for chirped oscillator automatic frequency control

Abstract

The starting frequency and sweep rate of a chirped frequency-shift-keyed oscillator are automatically controlled for correction of long-term drift. The substantially linear swept frequency output of the oscillator, during each of a successive multiplicity of swept frequency chirps, is counted and the count converted to an error signal utilized to control an appropriate potential in the oscillator circuit. The initial frequency is monitored, where the swept frequency range is small compared to the initial frequency, by counting the number of cyles during a chirp period in obtaining a first error signal from the total cycle count. The frequency-chirp ramp rate is monitored by counting the number of cycles during an initial portion, e.g. the first one-tenth, of the chirp interval, and comparing the count thus obtained with a frequency count obtained during an identical-length interval at the end of the frequency chirp; the count difference is utilized for automatic correction of change in frequency chirp sweep rate. Circuitry for implementation of initial frequency and/or sweep rate automatic correction is described.