Phase locked oscillator
AssigneeInternational Business Machines Corporation
InventorJohn Richard Taylor
Life of this patent
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Abstract
In a phase locked oscillator (PLO), the frequency of a voltage controlled oscillator (VCO) is changed in response to error signals indicating the phase error between the individual pulses of a stream of input pulses and the output pulses of the PLO. The running of the PLO is temporarily interrupted whenever the phase error exceeds a predetermined amount, and is restarted in phase with the next input pulse from the stream of pulses. A residual part of the error signal causing the interruption is accumulated so that after each interruption the frequency of the oscillator is closer to the frequency of the input stream of pulses. The process is repeated as required until phase lock is achieved.
Claims12
A phase locked oscillator comprising:
- a voltage controlled oscillator arranged to be controlled by an incoming controlliing signal consisting of a stream of pulses of substantially constant repetition rate;
- means for comparing the phase of the output from the voltage controlled oscillator with the phase of the controlling signal and for producing on receipt of each pulse of the controlling signal, an error signal indicative of any phase error existing between the incoming pulse and the oscillator output;
- means for converting each phase error signal to a corresponding voltage and for accumulating the voltages in a store which has a predetermined decay rate, the resulting error voltage being applied to the input of the oscillator so as to reduce the phase error;
- means for interrupting the oscillator output to the comparing means on detection of a phase error exceeding a predetermined amount and for resupplying the oscillator output to the comparing means in phase with a subsequent incoming control pulse, such that voltage is accumulated in the store until it is of sufficient magnitude to bring the frequency of the oscillator to the desired value to hold the phase lock.
Dependencies are inferred from the claim text.