INTEGRATED CIRCUIT WITH CALIBRATED PULLING EFFECT CORRECTION
A frequency-control circuit includes a phase frequency detector configured to receive a reference frequency signal and generate an output detection signal. The phase frequency detector can be configured to detect a difference in phase and frequency between the reference frequency signal and a feedback of the output frequency signal. The frequency-control circuit also includes a current source applied to the output detection signal to form a correction voltage that is a function of a pulling signal having one or more unwanted frequency components. The frequency-control circuit also includes a loop filter configured to filter the output detection signal including the correction voltage and generate a control voltage signal. The frequency-control circuit also includes a voltage-controlled oscillator configured to receive the control voltage signal and generate an output frequency signal.
1 . A frequency-control circuit for reducing interference from a pulling signal having one or more unwanted frequency components, the frequency-control circuit comprising:
a phase frequency detector (PFD) configured to receive a reference frequency signal and generate an output detection signal;
a current source coupled to an output of the PFD, the current source configured to receive a baseband signal that is a function of the pulling signal and output a current source signal;
a loop filter coupled to an output of the current source and the output of the PFD, the loop filter configured to receive the output detection signal including the current source signal and generate a control voltage signal having a correction voltage that corrects for the one or more unwanted frequency components of the pulling signal; and
a voltage-controlled oscillator (VCO) coupled to an output of the loop filter, the VCO configured to receive the control voltage signal with the correction voltage and generate an output frequency signal having a reduced number of the one or more unwanted frequency components of the pulling signal,
wherein the PFD is further configured to detect a difference in phase and frequency between the reference frequency signal and a feedback of the output frequency signal.
2 . The frequency-control circuit of claim 1 , wherein the output current signal is combined with the output detection signal through the loop filter to form the correction voltage at an input of the VCO.
3 . The frequency-control circuit of claim 1 , further comprising:
a processor configured to generate one or more components of the baseband signal based on a calibration of the output frequency signal, wherein the processor is further configured to compute one or more components of the baseband signal that correspond to the one or more unwanted frequency components; and
a digital-to-analog converter configured to convert the baseband signal from the analog domain to the digital domain for output to the current source.
4 . The frequency-control circuit of claim 1 , wherein the correction voltage comprises phase and magnitude components associated with the one or more unwanted frequency components.
5 . The frequency-control circuit of claim 4 , wherein the pulling signal comprises second-order frequency components associated with a transmitted baseband signal.
6 . The frequency-control circuit of claim 5 , wherein the second-order frequency components of the transmitted baseband signal are greater than a magnitude threshold.
7 . The frequency-control circuit of claim 1 , wherein the pulling signal is generated by another frequency-control circuit.
8 . The frequency-control circuit of claim 1 , further comprising a frequency divider inserted in a feedback loop from the VCO to the PFD and configured to increase the feedback of the output frequency signal by N times the reference frequency signal, where N is a positive integer.
9 . The frequency-control circuit of claim 1 , further comprising a sigma-delta modulator inserted in a feedback loop from the VCO to the PFD and configured to increase the feedback of the output frequency signal by a fractional divide ratio of N/N+1 times the reference frequency signal, where N is a positive integer.
10 . The frequency-control circuit of claim 1 , further comprising:
calibration circuitry coupled to an output of the VCO,
wherein the calibration circuitry adjusts the VCO during a calibration state to vary the output frequency signal according to the correction voltage.
11 . An apparatus for reducing interference from a pulling signal having one or more unwanted frequency components, the apparatus comprising:
means for receiving a reference frequency signal and generating an output detection signal;
means for receiving a baseband signal that is a function of the pulling signal and outputting an output current signal;
means for receiving the output detection signal including the output current signal and generating a control voltage signal having a correction voltage that corrects for the one or more unwanted frequency components of the pulling signal; and
means for receiving the control voltage signal with the correction voltage and generating an output frequency signal having a reduced number of the one or more unwanted frequency components of the pulling signal.
12 . The apparatus of claim 11 , wherein the means for receiving the reference frequency signal comprises means for detecting a difference in phase and frequency between the reference frequency signal and a feedback of the output frequency signal.
13 . The apparatus of claim 11 , further comprising:
means for generating the baseband signal based on a calibration of the output frequency signal; and
means for converting the baseband signal from the analog domain to the digital domain for output to the means for receiving the baseband signal.
14 . The apparatus of claim 13 , wherein the means for generating the baseband signal comprises means for computing one or more components of the baseband signal that correspond to the one or more unwanted frequency components.
15 . The apparatus of claim 11 , wherein the correction voltage comprises phase and magnitude components associated with the one or more unwanted frequency components.
16 . The apparatus of claim 11 , wherein the pulling signal is generated by another frequency-control circuit operating at a center frequency that is proximate to a center frequency of the frequency-control circuit.
17 . The apparatus of claim 11 , further comprising a frequency divider inserted in a feedback loop from the VCO to the PFD and configured to increase the feedback of the output frequency signal by N times the reference frequency signal, where N is a positive integer.
18 . The apparatus of claim 11 , further comprising a sigma-delta modulator inserted in a feedback loop from the VCO to the PFD and configured to increase the feedback of the output frequency signal by a fractional divide ratio of N/N+1 times the reference frequency signal, where N is a positive integer.
19 . The apparatus of claim 11 , further comprising:
means for calibrating the means for generating the output frequency signal.
20 . The apparatus of claim 19 , wherein the means for calibrating comprises means for adjusting the means for generating the output frequency signal during a calibration state to vary the output frequency signal according to the correction voltage.