System and method for RC calibration using phase and frequency
First Claim
1. A method of calibrating a resistor-capacitor (RC) filter to a desired cutoff frequency, the method comprising:
- initializing the RC filter with a cutoff frequency;
filtering an input signal, indicative of the desired cutoff frequency, with the RC filter to provide a filter output signal having phase and frequency values;
adjusting the cutoff frequency of the RC filter, based on the phase and frequency values of the filter output signal, if the phase and frequency values do not satisfy a predetermined condition, wherein the predetermined condition is that the input signal is locked in frequency to the filter output signal and the filter output signal lags the input signal in phase by at least a specified threshold; and
repeating the filtering and adjusting until the phase and frequency values of the filter output signal satisfy the predetermined condition.
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Accused Products
Abstract
An RC filter is calibrated to a desired cutoff frequency by initializing the filter with a cutoff frequency. An input signal is filtered by the RC filter to provide a filter output signal having phase and frequency values. The cutoff frequency of the RC filter is adjusted based on the phase and frequency values of the filter output signal if the phase and frequency values do not satisfy a predetermined condition. The filtering and adjusting are repeated until the phase and frequency values of the filter output signal satisfy the predetermined condition. A calibration apparatus has a frequency generator, a resistor-capacitor (RC) filter, a phase comparator, a frequency detector, and a state machine. The phase comparator, frequency detector, and state machine are configured to calibrate the RC filter to a cutoff frequency specified by the reference signal based on a filter output signal of the RC filter.
20 Citations
17 Claims
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1. A method of calibrating a resistor-capacitor (RC) filter to a desired cutoff frequency, the method comprising:
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initializing the RC filter with a cutoff frequency; filtering an input signal, indicative of the desired cutoff frequency, with the RC filter to provide a filter output signal having phase and frequency values; adjusting the cutoff frequency of the RC filter, based on the phase and frequency values of the filter output signal, if the phase and frequency values do not satisfy a predetermined condition, wherein the predetermined condition is that the input signal is locked in frequency to the filter output signal and the filter output signal lags the input signal in phase by at least a specified threshold; and repeating the filtering and adjusting until the phase and frequency values of the filter output signal satisfy the predetermined condition. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A calibration apparatus comprising:
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a frequency generator configured to provide a reference signal; a resistor-capacitor (RC) filter configured to filter the reference signal and provide a filter output signal; a phase comparator coupled to receive the reference signal and the filter output signal; a frequency detector coupled to receive the reference signal and the filter output signal; and a state machine; wherein the phase comparator, the frequency detector, and the state machine are configured to calibrate a cutoff frequency of the RC filter to a value specified by the reference signal based on the filter output signal of the RC filter, and the RC filter is configured to be calibrated by varying a capacitance of a variable capacitor of the RC filter until the reference signal is locked in frequency to the output of the RC filter and the output of the RC filter lags the reference signal in phase by at least a specified threshold. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. A digital RC calibration circuit comprising:
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a phase comparator configured to receive a reference signal and a quadrature output of an RC filter; a frequency detector configured to receive the reference signal and the quadrature output of the RC filter; and a state machine configured to process outputs of the phase comparator and the frequency detector, respectively, to provide a capacitor code to a variable capacitor of the RC filter to calibrate the RC filter to a desired cutoff frequency; wherein the frequency detector comprises; a first N-bit counter having a CLEAR input coupled to a clock, and having a CLK input coupled to the input to the RC filter; a second N-bit counter having a CLEAR input coupled to the clock, and having a CLK input coupled to the in-phase output of the RC filter; and an N-bit comparator providing an output indicative of whether outputs of the first and second N-bit counters are equal. - View Dependent Claims (16, 17)
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Specification