Tunable oscillator with noise degeneration

An oscillator comprising:

• (a) means for producing an output signal having an output frequency, said producing means comprising:
• (i) an amplifier having an input and an output and a field effect transistor as an active element thereof;
• (ii) a resonator having a first port and a second port, used in a transmission mode as a feedback element in a feedback loop disposed between the input and the output of the amplifier;
• (iii) a voltage-controlled phase shifter having a control port, responsive to a control signal, for controlling the phase shift of signals fed thereto, and disposed in the feedback loop in series with the resonator;
• (iv) means for dividing signals from the feedback loop into at least a first path and a second path;
• and
• (v) a circulator having a first port, a second port and a third port, the first port of the circulator responsive to the signals in the first path, the second port of the circulator connected to the resonator;
• and
• (b) a discriminator circuit, using the resonator in the reflection mode, comprising:
• (i) a phase detector having a first and a second input port and an output port, the first input port responsive to signals from the third port of the circulator;
• (ii) a 90.degree. phase shifter having an input port and an output port, the input port responsive to the signals from the second path and the output port connected to the second input port of the phase detector;
• and
• (iii) means, responsive to the output port of the phase detector, for providing the control signal to the voltage-controlled phase shifter;
• and
• (c) means for:
• (i) producing a resonator control signals for tuning the resonator at the output frequency;
• (ii) producing a 90.degree. phase shifter control signal for tuning the 90.degree. phase shifter;
• and
• (iii) producing a voltage-controlled phase shifter coarse control signal for tuning the voltage-controlled phase shifter to produce a selected differentiated phase shift corresponding to the output frequency.

A microwave oscillator having an output signal with an output frequency comprising:

• (a) an amplifier having a GaAs MESFET as an active element;
• (b) a resonator, resonant at the output frequency and comprising an yttrium-iron-garnet filter, connected to the amplifier and having a high Q to reduce FM noise and to provide positive feedback signals;
• (c) a voltage-controlled phase shifter having an input port, an output port and a control port, the input port being fed by the amplifier and the output port coupled to the resonator;
• (d) phase detector means, responsive to signals out of the voltage-controlled phase shifter shifted by 90.degree. and a portion of the positive feedback signals, for providing signals representative of low frequency noise arising within the amplifier;
• (d) means, responsive to the signals out of the phase detector means, for providing a control signal to the control port of the voltage-controlled phase shifter and for degenerating said low frequency noise;
• and
• (f) means for:
• (i) providing a resonator control signal for tuning the resonator at the output frequency;
• (ii) providing a 90.degree. phase shifter control signal for tuning the phase shift to 90.degree. of the signals fed to the phase detector means from the voltage-controlled phase shifter;
• and
• (iii) providing a voltage-controlled phase shifter coarse control signal for tuning the voltage-controlled phase shifter to produce a selected differentiated phase shift corresponding to the output frequency.