Calibrating RF path delay and IQ phase imbalance for polar transmit system

• US 9,954,626 B2
• Filed: 08/08/2016
• Issued: 04/24/2018
• Est. Priority Date: 12/18/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Intel IP Corporation (Intel Corporation)
• Inventors: Belitzer, Alexander, Sogl, Bernhard
• Primary Examiner(s): Koeth, Michelle M
• Application Number:
  US15/231,379
• Publication Number:
  US 20160352439A1
• Time in Patent Office: 624 Days
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 17/104 of other parameters, e.g. DC offset, delay or propagation times
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion
• CPC Class Codes: H04B 2001/0433 with linearisation using feedback
• CPC Class Codes: H04H 20/12 Arrangements for observation, testing or troubleshooting
• CPC Class Codes: H04L 1/248 Distortion measuring systems measurement of non-linear distortion G01R23/20; measuring characteristics of individual pulses, e.g. deviation from pulse flatness, rise time, duration G01R29/02
• CPC Class Codes: H04L 27/361 Modulation using a single or unspecified number of carriers, e.g. with separate stages of phase and amplitude modulation
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
• CPC Class Codes: H04W 72/0473 the resource being transmission power

Abstract

A method of calibrating parameters for a polar transmitter (Polar TX) system includes receiving phase information derived from transmission information in a Polar TX for producing a radio frequency (RF) broadcast signal. An Inphase local oscillator (LO_I) signal and a quadrature phase local oscillator (LO_Q) signal are derived from a combination of a first signal and the phase information using a digital phase lock loop. A feedback receiver (FBR) receives the RF broadcast signal provided by the Polar TX. The LO_I signal and the LO_Q signal are mixed with the RF broadcast signal to obtain mixer output signals. RF path delay and IQ phase imbalance are concurrently determined as a function of the first signal and of the mixer output signals.

Claims

1. A feedback receiver (FBR) configured to receive a radio frequency (RF) transmission signal that is fed back to the FBR from a transmitter (TX) that is associated with the FBR, the FBR comprising:

a plurality of mixers configured;

to mix the RF transmission signal with an inphase local oscillator (LO_I) signal and a quadrature phase local oscillator (LO_Q) signal,

the RF transmission signal comprising amplitude modulation (AM) information and phase information derived from a baseband signal, and

the LO_I signal and the LO_Q signal derived from a signal comprising a combination of both the phase information and a variable first signal that is injected into the TX, and that is configured to be varied for measurement of the AM information and the phase information, and for calculation of RF path delay and IQ phase imbalance, and to obtain a plurality of mixer output signals based on the RF transmission signal, the LO signal, and the LO_Q signal;

processing circuitry configured to measure, responsive to the variation of the variable first signal, the AM information and the phase information from the plurality of mixer output signals; and

measuring circuitry configured to concurrently calculate the RF path delay as a function of variation of the variable first signal and calculate the IQ phase imbalance as a function of the amplitude of the variable first signal as the variable first signal is varied.

2. The FBR of claim 1 wherein the measuring circuitry monitors at least one of the measured AM information and the measured phase information to concurrently determine the RF path delay and the IQ phase imbalance as a function of the monitored at least one measured information, the plurality of mixer output signals, and the varied first signal.

3. The FBR of claim 1 wherein the variable first signal is injected into the transmitter by circuitry configured to combine the variable first signal with a function of the phase information of a modulated baseband signal.

4. The FBR of claim 1 wherein the concurrent calculation of the RF path delay and the IQ phase imbalance comprises calibration of the RF path delay.

5. The FBR of claim 1 wherein the AM information is periodic, the variable first signal is an FM signal (FM_tune) comprising a sinusoid, and calculation of the IQ phase imbalance comprises variation of the value of FM_tune in a plurality of discrete points for a full period of the AM information, measurement of the AM information as a function of each of the plurality of discrete points, and calculation of the magnitude |e| of the IQ phase imbalance as a function of FBR power.

6. The FBR of claim 5 wherein the LO_Q signal is a delayed version of the LO_I signal and the delay is ninety degrees plus the IQ phase imbalance, wherein the magnitude |e| of the IQ phase imbalance that is calculated as the function of FBR power is approximately the maximum power of the FBR divided by the average power of the FBR, for phase imbalances that are smaller than 20 degrees.

7. The FBR of claim 1 wherein the variable first signal comprises a sinusoid, and the RF path delay is calculated as the difference in amplitude at two points of variation of the AM information divided by the variable first signal.

8. A method of calibrating parameters in a polar transmitter (polar TX) system wherein a radio frequency (RF) transmission signal is fed back to a feedback receiver, (FBR) the method comprising:

receiving the RF transmission signal provided by the polar TX, the RF transmission signal comprising amplitude modulation (AM) information derived from a baseband signal, and also comprising phase information derived from the baseband signal;

deriving an inphase (I) local oscillator (LO_I) signal and a quadrature phase (Q) local oscillator (LO_Q) signal from a combination of both the received phase information and a variable first signal, the variable first signal configured to be varied for measurement of the AM information and the phase information, and for calculation of RF path delay and IQ phase imbalance;

mixing the LO_I signal and the LO_Q signal with the RF transmission signal to obtain mixer output signals;

responsive to variation of the variable first signal, processing the mixer output signals to measure the AM information and the phase information; and

processing the measured AM information and phase information to calculate the RF path delay as a function of the variation of the variable first signal, and calculate the IQ phase imbalance as a function of the amplitude of the variable first signal as the variable first signal is varied.

9. The method of claim 8 wherein the phase information comprises delayed phase information, and the calculated RF path delay and IQ phase imbalance is a function of a monitored amplitude of the measured AM information and of the varied first signal.

10. The method of claim 8 wherein the variable first signal is injected into the polar transmitter by a combiner that is configured to combine the variable first signal with a function of the phase information that is derived from a baseband signal in the polar TX.

11. The method of claim 8 wherein an RF digital to analog converter receives the amplitude modulation information and provides a component of the RF transmission signal provided by the polar TX.

12. The method of claim 8 wherein a plurality of mixers is configured to mix the LO_I signal and the LO_Q signal with the received RF transmission signal to provide the mixer output signals, wherein the mixer output signals are processed to obtain the phase information and the AM information for measurement, as the variable first signal is varied to concurrently determine the RF path delay and the IQ phase imbalance.

13. The method of claim 12 wherein the AM information is periodic, the variable first signal is a variable FM signal (FM_tune) comprising a sinusoid, and calculating the IQ phase imbalance comprises varying the value of FM_tune in a plurality of discrete points for a full period of the AM information, measuring the AM information as a function of each of the plurality of discrete points, and calculating the magnitude |e| of the IQ phase imbalance as a function of FBR power.

14. The method of claim 13 wherein the LO_Q signal is a delayed version of the LO_I signal and the delay is ninety degrees plus the IQ phase imbalance, wherein the magnitude |e| of the IQ phase imbalance that is calculated as the function of FBR power is approximately the maximum power of the FBR divided by the average power of the FBR, for phase imbalances that are smaller than 20 degrees.

15. The method of claim 13 wherein the RF path delay is determined as the difference in amplitude at two points of variation of the AM information divided by a function of the variable first signal.

16. A polar transmitter (polar TX) comprising:

a radio frequency (RF) digital to analog converter (RFDAC) configured to receive processed baseband information and provide amplitude modulation (AM) information as a first component of an RF transmission signal for broadcast; and

oscillator circuitry configured to receive a signal that comprises a combination of both phase modulation information of a baseband signal and a variable first signal that is configured to be varied for measurement of the AM information and the phase modulation information, and for calculation of RF path delay and IQ phase imbalance, and to provide an Inphase local oscillator (LO_I) signal, and a quadrature phase local oscillator (LO_Q) signal as an input to a feedback receiver (FBR),

wherein the polar TX is configured to provide the RF transmission signal to the FBR to determine both the RF path delay of the FBR and the IQ phase imbalance of the FBR, each as a function of at least one signal that results from a mixing of the RF transmission signal with the LO_I signal and the LO_Q signal as the variable first signal is varied over a sinusoidal period of the variable first signal to measure the AM information and the phase information.

17. The polar TX of claim 16 wherein the mixing is performed by a plurality of mixers configured to mix the radio frequency transmission signal with the LO_I signal and the LO_Q signal and provide a plurality of mixer output signals.

18. The polar TX of claim 17 wherein the plurality of mixer output signals are processed to derive the AM information and the phase modulation information from the plurality of mixer output signals, and wherein the AM information and the phase modulation information are measured as the variable first signal is varied, to concurrently determine the RF path delay of the FBR as a function of the variable first signal, and the IQ phase imbalance of the FBR as a function of the measured AM modulation information and the varied first signal.

19. The polar TX of claim 16 wherein the AM information comprises a signal having a substantially sinusoid trajectory.

20. The polar TX of claim 19 wherein the RF path delay is calculated as the difference in amplitude of the substantially sinusoid trajectory at two points of variation of the variable first signal, and division of the difference by a function of the variable first signal.

21. A polar transmitter (polar TX) system comprising:

a polar TX that comprises;

a radio frequency (RF) digital to analog converter to receive processed first amplitude modulation (AM) information as a first component of an RF transmission signal for broadcast;

oscillator circuitry configured to receive a signal that comprises a combination of both phase modulation information from a baseband signal, and a variable first signal that is configured to be varied for calculation of RF path delay and IQ phase imbalance, to provide phase modulation information as a second component of the RF transmission signal and to further provide an Inphase local oscillator (LO_I) signal and a quadrature phase local oscillator (LO_Q) signal;

a feedback receiver (FBR) that is configured to receive the RF transmission signal, the LO_I signal and the LO_Q signal, the FBR comprising;

at least one mixer configured to mix the RF transmission signal with the LO_I signal and the LO_Q signal and provide a plurality of mixer output signals, processing circuitry configured to derive the AM information and the phase information from the plurality of mixer output signals, and

measuring circuitry configured to measure the AM information and the phase information, as the variable first signal is varied, to concurrently determine both the RF path delay as a function of variation of the variable first signal, and the IQ phase imbalance as a function of the amplitude of the variable first signal as the variable first signal is varied.

22. The Polar TX system of claim 21 wherein the measuring circuitry further derives at least a second AM information from at least one of the mixer output signals, varies the variable first signal and measures the variation of the second AM information as the variable first signal is varied to determine the RF path delay and the IQ phase imbalance.

23. The polar TX system of claim 21 wherein the RF path delay is calculated by the difference in amplitude of a signal having a substantially sinusoid trajectory at two points of variation of the variable first signal and the division of the difference by a function of the variable first signal.