Calibration arrangement for frequency synthesizers

• US 9,197,403 B2
• Filed: 07/20/2012
• Issued: 11/24/2015
• 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: Gauthier, Laurent, Delbecq, Dominique, Vigier, Jean-Stephane
• Primary Examiner(s): Perez, James M
• Application Number:
  US14/415,961
• Publication Number:
  US 20150146835A1
• Time in Patent Office: 1,222 Days
• Field of Search: 375354-376
• US Class Current: 1/1
• 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 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 phase comparator output for generating a phase difference signal;

a voltage controlled oscillator having a first control input coupled to receive the phase difference signal 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 inputs;

a divider having a first input coupled to receive the oscillation signal and an output for generating the feedback signal by dividing the oscillation signal by a divisor, the divisor of the divider being programmed based on a divisor control signal received via a divisor input; and

a modulation unit having a modulation input for receiving a modulation signal, a first modulation output to provide the second control signal, and a second modulation output to provide the divisor control signal, and a change of the modulation signal generates a predefined change of the second control signal and a change of the divisor via the divisor control signal that is proportional to said predefined change; and

the calibration arrangement comprising;

a calibration input for receiving the phase difference signal;

a ripple detector for providing a ripple 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 generating a calibration control signal based on the ripple detector output signal,

wherein the second control signal is adjusted based on the calibration control signal such that the detected ripple is reduced.

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

the first sample and hold unit being arranged for generating the first 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 further 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 signal by sampling on negative edges in the modulation signal, and

the detector unit 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 further 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 unit 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 unit is a comparator.

6. The device as claimed in claim 2, wherein the detector unit is a multi-threshold comparator.

7. The device as claimed in claim 1, wherein the voltage controlled oscillator is a digital voltage controlled oscillator.

8. The device as claimed in claim 1, wherein the device further 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 second control signal is adjusted by setting a modulation gain.

10. The device as claimed in claim 9, wherein setting the modulation gain uses successive approximation operations.

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 method comprising:

generating, by a phase comparator of the circuit, a phase difference signal representing the phase difference between a feedback signal and a reference frequency, the feedback signal and the reference frequency being respectively received at first and second inputs of the phase comparator;

generating, by a voltage controlled oscillator of the circuit, an oscillator signal at an oscillation frequency controlled by the phase difference signal and a second control signal respectively received at first and second control inputs of the voltage controlled oscillator;

generating, by a divider of the circuit, the feedback signal by dividing the oscillation signal by a divisor, the divisor being programmed based on a divisor control signal received via a divisor input of the divider;

receiving a modulation signal at a modulation unit of the circuit;

generating, by the modulation unit, the second control signal of the voltage controlled oscillator and the divisor control signal based at least in part on the received modulation signal, and a change of the modulation signal generates a predefined change of the second control signal and a change of the divisor via the divisor control signal that is proportional to said predefined change;

receiving the phase difference signal at a calibration input of a calibration arrangement;

detecting, via a ripple detector of the calibration arrangement, a ripple on the phase difference signal correlated to edges in the modulation signal; and

generating, via a calibration control unit, a calibration control signal based on the results of the ripple detector,

wherein the second control signal is adjusted based on the calibration control signal such that the detected ripple is reduced.

13. The method as claimed in claim 12, wherein detecting the ripple further comprises generating at least a first sample and hold output signal by sampling the phase difference signal on edges in the modulation signal, and detecting the ripple on the at least first sample and hold output signal using a detector unit.

14. The method as claimed in claim 13, wherein detecting the ripple further comprises:

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

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

detecting, via the detector unit, a difference between the first sample and hold output signal and the second sample and hold output signal.

15. The method as claimed in claim 13, wherein detecting the ripple further comprises generating a reference signal by low-pass filtering the phase difference signal, and detecting a difference between the at least first sample and hold output signal and the reference signal using the detector unit.

16. The method as claimed in claim 12, wherein the second control signal is adjusted by setting a modulation gain.

17. The method as claimed in claim 16, wherein setting the modulation gain uses a successive approximation process.