Phase switching PLL and calibration method

Patent metadata

Field	Value
Publication number	US-9356609-B1
Application number	US-201414576691-A
Country	US
Kind code	B1
Filing date	Dec 19, 2014
Priority date	Dec 19, 2014
Publication date	May 31, 2016
Grant date	May 31, 2016

Abstract

The phase-locked loop (PLL) presented herein controls the phase of the output of the PLL. To that end, the PLL includes an oscillator that generates an output signal at an output of the PLL responsive to a comparison between a reference signal input to the PLL and a feedback signal derived from the output signal. To control the phase of the output signal, a modulation signal is applied to one input of the oscillator, separate from the reference signal input, where the modulation signal comprises one or more pulses having a total area defined based on the desired phase shift. To maintain the desired phase shift at the output of the PLL, the PLL also sets a time relationship between the reference signal and the feedback signal based on the desired phase shift.

First claim

What is claimed is:

1. A phase-locked loop (PLL) comprising:
an oscillator configured to generate an output signal at an output of the PLL responsive to a reference signal input to the PLL, the oscillator including a primary control input and a separate auxiliary control input;
a detector configured to compare the reference signal to a feedback signal to generate one or more PLL control signals, the feedback signal being derived by a feedback loop of the PLL from the output signal; and
a phase control system configured to control a phase of the output signal to achieve a desired phase shift at the output of the PLL, the phase control system comprising:
a modulation circuit operatively coupled to the oscillator and configured to execute open loop phase control of the PLL by:
generating a phase modulation signal comprising one or more pulses having a total area defined based on the desired phase shift; and
applying the phase modulation signal to the auxiliary control input to change the phase of the output of the PLL to achieve the desired phase shift; and

a phase skew circuit configured to execute closed-loop phase control of the PLL to maintain the phase of the output of the PLL at the desired phase shift by setting a time relationship between the reference signal and the feedback signal based on the desired phase shift.

2. The PLL of claim 1 wherein the total area of the one or more pulses of the phase modulation signal is derived from a fixed pulse amplitude and one or more variable pulse durations defined based on the desired phase shift.

3. The PLL of claim 1 wherein the PLL comprises:
a charge pump operatively connected between the detector and the primary control input of the oscillator; and
a loop filter operatively connected between the charge pump and the primary control input of the oscillator,
wherein the phase skew circuit is configured to set the time relationship between the reference signal and the feedback signal by injecting a current into the loop filter or by leaking the current out of the loop filter, wherein the phase skew circuit sets the magnitude of the injected or leaked current based on the desired phase shift.

4. The PLL of claim 1 wherein the phase skew circuit is configured to set the time relationship between the reference signal and the feedback signal by applying a time delay determined based on the desired phase shift to at least one of the reference signal and the feedback signal such that the time relationship between the reference signal and the feedback signal is established based on the desired phase shift.

5. The PLL of claim 1 wherein the output of the PLL is operatively coupled to an antenna element of an antenna array of at least one of a beam-forming transmitter and a beam-forming receiver, and wherein the PLL is used to at least one of downconvert signals received by the antenna element and upconvert signals to be transmitted by the antenna element.

6. The PLL of claim 5 wherein one of the phase control system and an external array control circuit selects the desired phase shift based on a location of the antenna element in the antenna array and at least one of a desired beam direction and beam shape of the beam-forming transmitter or receiver.

7. The PLL of claim 1 wherein the phase control system further comprises a control circuit configured to generate the phase modulation signal for the open-loop phase control based on the desired phase shift, and wherein the control circuit is further configured to define the time relationship between the reference signal and the feedback signal for the closed-loop phase control based on the desired phase shift.

8. The PLL of claim 1 further comprising a calibration circuit configured to calibrate, for at least one carrier frequency set by the PLL, the phase modulation signal for one or more desired phase shifts based on a calibration control signal derived from one or more PLL measurements.

9. The PLL of claim 8 wherein the calibration circuit calibrates the phase modulation signal by calibrating an amplitude of the one or more pulses of the phase modulation signal for each of the one or more desired phase shifts based on the calibration control signal.

10. The PLL of claim 8 wherein the calibration control signal comprises a loop voltage of the PLL.

11. A method of controlling a phase at an output of a phase-locked loop (PLL) to achieve a desired phase shift at the output of the PLL, the PLL comprising an oscillator configured to generate an output signal at the output of the PLL responsive to a reference signal input to the PLL, the oscillator including a primary control input and a separate auxiliary control input, and a detector configured to compare the reference signal to a feedback signal to generate one or more PLL control signals, the feedback signal being derived by a feedback loop of the PLL from the output signal, the method comprising:
executing open-loop phase control of the PLL by:
generating a phase modulation signal comprising one or more pulses having a total area defined based on the desired phase shift; and
applying the phase modulation signal to the auxiliary control input to change the phase of the output of the PLL to achieve the desired phase shift; and

executing closed-loop phase control of the PLL to maintain the phase of the output of the PLL at the desired phase shift by setting a time relationship between the reference signal and the feedback signal based on the desired phase shift.

12. The method of claim 11 further comprising defining the total area of the one or more pulses of the phase modulation signal based on a fixed pulse amplitude and one or more variable pulse durations defined based on the desired phase shift.

13. The method of claim 11 wherein the PLL comprises a charge pump operatively connected between the detector and the primary control input of the oscillator and a loop filter operatively connected between the charge pump and the primary control input of the oscillator, and wherein setting the time relationship between the reference signal and the feedback signal comprises injecting a current into the loop filter or by leaking the current out of the loop filter, wherein the phase skew circuit sets the magnitude of the injected or leaked current based on the desired phase shift.

14. The method of claim 11 further comprising determining a time delay based on the desired phase shift, wherein setting the time relationship between the reference signal and the feedback signal comprises applying the time delay to at least one of the reference signal and the feedback signal such that the time relationship between the reference signal and the feedback signal is established based on the desired phase shift.

15. The method of claim 11 wherein the output of the PLL is operatively coupled to an antenna element of an antenna array of at least one of a beam-forming transmitter and a beam-forming receiver, the method further comprising using the PLL to at least one of downconvert signals received by the antenna element and upconvert signals to be transmitted by the antenna element.

16. The method of claim 15 further comprising selecting the desired phase shift based on a location of the antenna element in the antenna array and at least one of a desired beam direction and beam shape of the beam-forming transmitter or receiver.

17. The method of claim 11 further comprising calibrating, for at least one carrier frequency set by the PLL, the phase modulation signal for one or more desired phase shifts based on a calibration control signal derived by

Assignees

• Ericsson Telefon Ab L M

Inventors

• Ek Staffan
• Påhlsson Tony
• Sjöland Henrik
• Sundström Lars

Classifications

• H03L7/099

  concerning mainly the controlled oscillator of the loop · CPC title

• H03L7/0891

  the up-down pulses controlling source and sink current generators, e.g. a charge pump · CPC title

• H03L2207/06

  Phase locked loops with a controlled oscillator having at least two frequency control terminals · CPC title

• H03L7/085 Primary

  concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal (H03L7/10 takes precedence; circuits for comparing the phase or frequency of two mutually-independent oscillations H03D13/00) · CPC title

• H03K5/19 Primary

  Monitoring patterns of pulse trains (indicating amplitude G01R19/00; indicating frequency G01R23/00; measuring characteristics of individual pulses G01R29/02) · CPC title