Control circuit for low noise frequency agile oscillator

Claim 1

A control ciruit for a voltage-controlled oscillator, such circuit comprising: (a) means receiving the output signal of the voltage-controlled oscillator, for deriving from said output signal an output representative signal; (b) means for equally splitting the output representative signal to form a first, second and third signal in corresponding first, second and third paths; (c) delay means and variable attenuating means disposed, respectively, in the first and the second path; (d) means for vectorially subtracting the delayed first and the attenuated second signals in the first and the second paths to form a fourth signal having an amplitude and phase, relative to the output signal of the voltage-controlled oscillator, indicative of the instantaneous frequency of said output signal; (e) means for dividing the third signal into a reference signal and a phase-shifted reference signal in quadrature with the reference signal; (f) first phase detector means responsive to the phase shifted reference signal and to the fourth signal, and second phase detector means responsive to the reference signal and to the fourth signal, said first phase detector means providing an error signal to control the frequency of the voltage-controlled oscillator and said second phase detector means providing an attenuator control signal to control the fourth signal, thereby ultimately to stabilize the frequency of the output signal of the voltage-controlled oscillator.