Charge-based frequency locked loop and method
First Claim
1. A frequency locked loop (FLL) comprising:
- a charge integrating amplifier;
a voltage controlled oscillator which operates in response to an output voltage from said amplifier;
a switched-capacitor circuit for providing an input current to said amplifier which is a function of a combination of a reference current related to a reference frequency and a feedback current related to an output frequency of said voltage controlled oscillator,whereby the input current varies in response to the output frequency to lock the FLL on a frequency.
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Abstract
A frequency locked loop (FLL) having an oscillator whose output frequency controls the amount of charge provided by a switched feedback capacitor to a charge integrator whose output voltage controls the frequency of the oscillator. A switched reference capacitor provides a charge to the charge integrator which is a function of a reference frequency, so that the oscillator output frequency is a function of a product of the reference frequency times a ratio of the capacitance of the reference capacitor to the capacitance of the feedback capacitor. Plural reference capacitors, each responsive to a respective reference frequency may be provided so that the oscillator output frequency can be related to the sums or differences of the reference frequencies, the ratios of capacitors, the ratio of the reference voltages or a fixed multiplication factor.
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Citations
26 Claims
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1. A frequency locked loop (FLL) comprising:
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a charge integrating amplifier; a voltage controlled oscillator which operates in response to an output voltage from said amplifier; a switched-capacitor circuit for providing an input current to said amplifier which is a function of a combination of a reference current related to a reference frequency and a feedback current related to an output frequency of said voltage controlled oscillator, whereby the input current varies in response to the output frequency to lock the FLL on a frequency. - View Dependent Claims (2, 3, 4, 5)
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- 6. A charge-based frequency locked loop (FLL) comprising an oscillator whose output frequency controls the amount of charge provided by a switched feedback capacitor to a charge integrator whose output voltage controls the frequency of said oscillator.
- 16. A method of frequency locking a frequency of an output from an oscillator comprising the steps of using an output frequency from the oscillator to control the amount of charge provided by a switched feedback capacitor to a charge integrator, and using an output voltage of the charge integrator to control the output frequency of the oscillator.
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26. A method of setting a bandwidth of a frequency locked loop (FLL) independently of an output frequency of an oscillator in the FLL, the method comprising the steps of:
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(a) using an output frequency from the oscillator to control the amount of charge provided by a switched feedback capacitor to a charge integrator; (b) providing a charge from a switched reference capacitor to the charge integrator which is a function of a reference frequency; (c) using an output voltage of the charge integrator to control the output frequency of the oscillator; (d) charging the reference capacitor with a first reference voltage and charging the feedback capacitor with a second reference voltage; (e) setting a bandwidth of the FLL by adjusting magnitudes of the first and second reference voltages; and (f) scaling the magnitudes of the first and second reference voltages by the same factor so that the output frequency is independent of changes in the loop bandwidth.
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Specification