Phase-locked loop with clamped voltage-controlled oscillator
First Claim
1. A circuit receiving an input signal and generating an output signal, comprising:
- first and second voltage controlled oscillators, said first voltage controlled oscillator providing a control signal, said second voltage controlled oscillator operatively coupled to said input signal and providing said output signal; and
constraining means receiving said control signal for limiting the voltage swing at an input terminal of said second voltage controlled oscillator to thereby constrain the frequency range of operation of said second voltage controlled oscillator in accordance with said control signal, wherein said constraining means comprises a clamping circuit.
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Accused Products
Abstract
A phase-locked loop responsive to both phase and frequency difference between the incoming signal and the feedback signal is provided. Using a reference signal, this phase-locked loop accepts a wide range of frequencies similar to a phase-locked loop having a phase frequency detector, and also achieves the noise performance of a phase-locked loop having only a simple phase detector. In one embodiment, the phase-locked loop is a combination including first and second phase-locked loops. The reference signal is provided to the first phase-locked loop, which includes a phase frequency detector. This first phase-locked loop is used to control a second phase-locked loop, which includes a phase detector. A voltage clamp can also be provided to enhance the ability to lock a signal among several signals, or from a noisy background.
90 Citations
25 Claims
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1. A circuit receiving an input signal and generating an output signal, comprising:
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first and second voltage controlled oscillators, said first voltage controlled oscillator providing a control signal, said second voltage controlled oscillator operatively coupled to said input signal and providing said output signal; and constraining means receiving said control signal for limiting the voltage swing at an input terminal of said second voltage controlled oscillator to thereby constrain the frequency range of operation of said second voltage controlled oscillator in accordance with said control signal, wherein said constraining means comprises a clamping circuit. - View Dependent Claims (2)
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3. A circuit receiving an input signal and generating an output signal, comprising:
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first and second phase-locked loops said first phase-locked loop providing a control signal, said second phase-locked loop receiving said input signal and providing said output signal; and constraining means receiving said control signal for limiting the voltage swing at an input terminal of said second phase-locked loop to thereby constrain the frequency range of operation of said second phase-locked loop in accordance with said control signal, wherein said constraining means comprises a clamping circuit. - View Dependent Claims (4)
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5. An apparatus receiving first and second input signals, said apparatus comprising:
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(a) a first phase-locked loop receiving said first input signal and providing a center frequency based on said first input signal comprising; (i) first voltage-controlled oscillator for receiving a phase and frequency correction signal, and for providing a first feedback signal responsive to said phase and frequency correction signal; and (ii) phase frequency detector and filter means for detecting a phase and frequency difference between said first input signal and said first feedback signal, and for providing said phase and frequency correction signal responsive to said phase and frequency difference; (b) a second phase-locked loop receiving said second input signal comprising; (i) second voltage-controlled oscillator, substantially the same as said first voltage-controlled oscillator, for receiving a correction signal, and for providing a second feedback signal responsive to said correction signal; and (ii) phase detector and filter means for detecting a phase difference between said second input signal and said second feedback signal, and for providing a phase correction signal responsive to said phase difference; (c) constraining means constraining the frequency range of said second phase-locked loop such that said second phase-locked loop locks on said second input signal if said second input signal is within a pull-in range centered around said center frequency, comprising; (i) summation means for receiving said phase and frequency correction signal and said phase correction signal and for providing a summed signal to said second voltage controlled oscillator; and (ii) a voltage clamp connecting said phase and frequency detector and filter means, such that the difference between said phase and frequency correction signal and said phase correction signal is constrained to within a predetermined voltage interval. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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Specification