CALIBRATION ARRANGEMENT FOR FREQUENCY SYNTHESIZERS

• US 20150146835A1
• Filed: 07/20/2012
• Published: 05/28/2015
• Est. Priority Date: 07/20/2012
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Delbecq, Dominique, Gauthier, Laurent, Vigier, Jean Stphane
• Granted Patent: US 9,197,403 B2
• Time in Patent Office: Days
• US Class Current: 375/376
• CPC Class Codes: H03C 3/0925 applying frequency modulation at the divider in the feedback loop
• CPC Class Codes: H03L 7/197 a time difference being used for locking the loop, the counter counting between numbers which are variable in time or the frequency divider dividing by a factor variable in time, e.g. for obtaining fractional frequency division H03L7/1806 takes precedence
• CPC Class Codes: H04L 7/0331 with a digital phase-locked loop [PLL] processing binary samples, e.g. add/subtract logic for correction of receiver clock H04L7/0337 takes precedence

Abstract

An electronic device has a calibration arrangement for controlling a frequency characteristic of a PLL circuit having a phase comparator having an output for generating a phase difference signal, a voltage controlled oscillator and a divider. The divisor of the divider is programmable, and the oscillator is also directly modulated by an oscillator modulation signal. A modulation unit has a modulation input for receiving a modulation signal and generates the oscillator modulation signal and the divisor such that modulation generates a predefined change of the output frequency and a change of the divisor proportional to said predefined change. The calibration arrangement receives the phase difference signal, and has a ripple detector for providing a detector output signal by detecting a ripple on the phase difference signal correlated to edges in the modulation signal. A calibration control unit adjusts the oscillator modulation signal based on the detector output signal such that the ripple is reduced.

Claims

1. An electronic device, the device 4 comprising a calibration arrangement for controlling a frequency characteristic of a circuit, the circuit comprising

a phase comparator having a first input for receiving a feedback signal and a second input for receiving a reference frequency and a comparator output for generating a phase difference signal,

a voltage controlled oscillator having a first control input coupled to the phase comparator output and a second control input for receiving a second control signal, and an oscillator output for outputting an oscillator signal at an oscillation frequency controlled by the first and second control input,

a divider having an input coupled to the oscillation signal and an output for generating the feedback signal, the divisor of the divider being programmable via a divisor input,

a modulation unit having a modulation input for receiving a modulation signal and a first modulation output coupled to the second control input of the voltage controlled oscillator and a second modulation output coupled to the divisor input such that a change of the modulation signal generates a predefined change of the output frequency and a change of the divisor proportional to said predefined change,

the calibration arrangement comprising:

a calibration input for receiving the phase difference signal;

a ripple detector for providing a detector output signal by detecting a ripple on the phase difference signal correlated to edges in the modulation signal; and

a calibration control unit for adjusting the second control signal based on the detector output signal such that the ripple is reduced.

2. The device as claimed in claim 1, wherein the ripple detector comprises at least one sample and hold unit coupled to the calibration input, and a detector having a detector input coupled to a sample and hold output signal of the sample and hold unit,

the sample and hold unit being arranged for generating the sample and hold output signal by sampling on edges in the modulation signal.

3. The device as claimed in claim 2, wherein the ripple detector comprises a second sample and hold unit coupled to the calibration input,

said first sample and hold unit being arranged for generating the first sample and hold output signal by sampling on positive edges in the modulation signal, and

the second sample and hold unit being arranged for generating a second sample and hold output by sampling on negative edges in the modulation signal, and

the detector having a second detector input coupled to the second sample and hold output signal, and being arranged for detecting a difference between said first detector input and the second detector input.

4. The device as claimed in claim 2, wherein the ripple detector comprises a low-pass filter coupled to the calibration input, the low-pass filter being arranged for generating a reference signal by low-pass filtering the phase difference signal, and

the detector having a second detector input coupled to the reference signal, and being arranged for detecting a difference between said first detector input and the second detector input.

5. The device as claimed in claim 2, wherein the detector comprises a comparator for providing the detector output signal.

6. The device as claimed in claim 2, wherein the detector comprises a multi threshold comparator for providing, as the detector output signal, a respective one of a set of output values when the phase difference signal exceeds a respective threshold of multiple thresholds.

7. The device as claimed in claim 1, wherein the device comprises a digitally controlled oscillator constituting the voltage controlled oscillator.

8. The device as claimed in claim 1, wherein the device comprises a phase locked loop comprising the phase comparator, the divider and the modulation unit.

9. The device as claimed in claim 1, wherein the calibration arrangement is arranged for said adjusting the second control signal by setting a modulation gain.

10. The device as claimed in claim 9, wherein the calibration arrangement is arranged for setting the modulation gain via changes of said gain according to a successive approximation process.

11. An integrated circuit comprising at least one electronic device according to claim 1.

12. A method of controlling a frequency characteristic of a circuit of an electronic device, the circuit comprising

a phase comparator having a first input for receiving a feedback signal and a second input for receiving a reference frequency and a comparator output for generating a phase difference signal,

a voltage controlled oscillator having a first control input coupled to the comparator output and a second control input for receiving a second control signal, and an oscillator output for outputting an oscillator signal at an oscillation frequency controlled by the first and second control input,

a divider having an input coupled to the oscillation signal and an output for generating the feedback signal, the divisor of the divider being programmable via a divisor input,

a modulation unit having a modulation input for receiving a modulation signal and a first modulation output coupled to the second control input of the voltage controlled oscillator and a second modulation output coupled to the divisor input such that a change of the modulation signal generates a predefined change of the output frequency and a change of the divisor proportional to said predefined change, the method comprising

receiving the phase difference signal;

detecting a ripple on the phase difference signal correlated to edges in the modulation signal;

adjusting the second control signal based on the detector output signal such that the ripple is reduced.

13. The method as claimed in claim 12, wherein the ripple detector comprises at least one sample and hold unit coupled to the calibration input, and the method comprises generating a sample and hold output signal by sampling on edges in the modulation signal, and detecting the ripple on the sample and hold output signal.

14. The method as claimed in claim 13, wherein the ripple detector comprises a second sample and hold unit coupled to the calibration input, and the method comprises

generating, via said first sample and hold unit, the first sample and hold output signal by sampling on positive edges in the modulation signal;

generating, via the second sample and hold unit, a second sample and hold output by sampling on negative edges in the modulation signal; and

detecting a difference between first sample and hold output signal and the second sample and hold output signal.

15. The method as claimed in claim 13, wherein the ripple detector comprises a low-pass filter coupled to the calibration input, the low-pass filter being arranged for generating a reference signal by low-pass filtering the phase difference signal, and the method comprises

detecting the detector a difference between the sample and hold output signal and the reference signal.

16. The method as claimed in claim 13, wherein the method comprises detecting a respective one of a set of output values when the difference of the difference peak signal and the reference signal exceeds a respective threshold of multiple thresholds.

17. The method as claimed in claim 12, wherein the method comprises adjusting the second control signal by setting a modulation gain.

18. The method as claimed in claim 17, wherein the method comprises setting the modulation gain via changes of said gain according to a successive approximation process.