Voltage controlled crystal oscillator with reduced oscillations at crystal overtones
First Claim
1. A crystal controllable oscillator circuit comprising an amplifier having an input for coupling a crystal resonator thereto and having an output, an oscillation sustaining feed-back loop coupled between the output and the input of the amplifier, the loop including a first integrator and a second integrator fed from the first integrator whereby overtone oscillations are inhibited.
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Abstract
The invention relates to a crystal controllable oscillator circuit. The oscillator includes an amplifier and an oscillation sustaining feed-back loop coupled between an output and an input of the amplifier the loop including two integrators in series for inhibiting oscillation at crystal overtones. Each integrator provides 90° phase shift independently of the oscillators defining RC product which determines only the gain thereby making the oscillator less sensitive to variations in circuit time constants due to temperature and manufacturing tolerance effects. The invention is particularly suitable for incorporating in integrated circuit form where only a single pin connection is required for the controlling crystal.
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Citations
11 Claims
- 1. A crystal controllable oscillator circuit comprising an amplifier having an input for coupling a crystal resonator thereto and having an output, an oscillation sustaining feed-back loop coupled between the output and the input of the amplifier, the loop including a first integrator and a second integrator fed from the first integrator whereby overtone oscillations are inhibited.
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11. A crystal controllable oscillator circuit comprising a differential amplifier having an output and first and second inputs;
- a crystal circuit coupled between the first input and a supply terminal;
an oscillation sustaining feed-back loop coupled to the output of the differential amplifier, the loop including a first integrator and a second integrator fed from the first integrator, means coupling an output of the second integrator to the first and second inputs of the differential amplifier;
a frequency control circuit having an input coupled to the output of the second integrator and an output coupled to feed an adjustable amplitude frequency control signal to a control input of the second integrator and an auxiliary negative feed-back loop having relatively low gain at oscillator signal frequencies coupled to the differential amplifier for establishing quiescent D. C. biasing for the amplifier whereby to provide an adjustable frequency crystal controllable oscillator in which oscillations at crystal overtones are inhibited.
- a crystal circuit coupled between the first input and a supply terminal;
Specification