VFO having plural feedback loops
AssigneeRCA Corporation
InventorsJames A. Wilber, Todd J. Christopher
Life of this patent
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Abstract
An oscillator including a resonator having a primary feedback loop for causing oscillations to occur at a desired frequency and a secondary feedback loop including a multiplier for causing variations of said frequency in response to an input signal manifestation. Spectral purity is enhanced and potential overtone oscillations are suppressed by a cascade connection of lag networks in the primary loop which exhibit a low-pass transfer characteristic and provide at least .pi. radians of phase shift, one of the networks being shared in common with the secondary loop for supplying a quadrature signal to the multiplier.
Claims12
In an oscillator of the kind comprising a piezoelectric crystal having first and second plates, a primary feedback loop coupled to said crystal for causing output signal oscillations to occur at a desired frequency and a secondary feedback loop coupled to said crystal and including a multiplier for causing variations of said desired frequency in response to a control signal manifestation, the improvement for enhancing spectral purity of the output signal and for suppressing tendencies toward overtone oscillation, said improvement comprising:
- a cascade connection of first (14) and second (16) 90.degree. phase lag networks in said primary feedback loop (14, 16, 18, 10) for providing a lowpass transfer characteristic and .pi. radians of phase shift in the primary loop, the first network (14) having an input coupled to said second plate of said crystal, the second network (16) having an input coupled to an output of the first network and having an output coupled to said first plate of said crystal;
- inverter means (18) connected in series with said second network between said output of said first network and said first plate of said crystal for imparting an additional .pi. radians of phase shift to said primary feedback loop;
- means coupling said output of said first network (14) to a first input of said multiplier (20) whereby the first one of said networks in said cascade connection is shared in common with the secondary loop and supplies a quadrature input signal to said multiplier;
- and
- means for deriving said output signal from the output of the second of said networks in said cascade connection.
In an oscillator of the kind comprising a piezoelectric crystal having first and second plates, a primary feedback loop coupled to said crystal for causing output signal oscillations to occur at a desired frequency and a secondary feedback loop coupled to said crystal and including a multiplier for causing variations of said desired frequency in response to a control signal manifestation, the improvement for enhancing spectral purity of the output signal and for suppressing tendencies toward overtone oscillation, said improvement comprising:
- a cascade connection of a plurality of 90.degree. phase lag networks in said primary feedback loop for providing a lowpass transfer characteristic and at least .pi. radians of phase shift in the primary loop;
- the first one of said networks in said cascade connection being shared in common with the secondary loop for supplying a quadrature input signal to said multiplier;
- means for deriving said output signal from the last one of said networks in said cascade connection;
- a vector summation circuit for vectorally combining signals in said feedback loops, said summation circuit having a first input coupled to an output of a last one of said phase lag networks for receiving a fixed magnitude vector signal, having a second input coupled to an output of said multiplier for receiving a variable magnitude vector signal and having an output coupled to said first plate of said crystal for supplying a composite vector signal thereto;
- a first circuit for producing at an output thereof a second composite vector signal having an antiphase relationship with the first mentioned composite vector signal;
- and
- a neutralization circuit for coupling said second composite signal to said second plate of said crystal.
Dependencies are inferred from the claim text.