ADAPTIVE IIP2 CALIBRATION

• US 20100093298A1
• Filed: 10/09/2008
• Published: 04/15/2010
• Est. Priority Date: 10/09/2008
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: PRATT, PATRICK, SOBCHAK, CHARLES LEROY
• Granted Patent: US 8,060,043 B2
• Time in Patent Office: Days
• US Class Current: 455/226.1
• CPC Class Codes: H04B 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements

Abstract

A radio frequency transceiver (102), including a transmitter (104), a duplexer (108) and a direct-conversion receiver (106) including a mixer (140 and 141). An IIP2 calibration system (170), coupled to the transceiver, includes an IIP2 coefficient estimator (172) for calculating an estimate of second-order distortion intermodulation distortion, and an IIP2 controller (174) for adjusting an IIP2 tuning port of the mixer in the receiver to minimize second-order distortion intermodulation distortion in the receiver that may be caused by the receiver receiving a transmit RF signal leaking through the duplexer.

Claims

1. An input-related, second-order intercept point (IIP2) calibration system for a receiver of a transceiver including a transmitter, comprising:

an estimator, coupled to a transmitter of a transceiver and to a receiver of the transceiver, for calculating an estimate of second-order intermodulation distortion in the receiver as a result of second-order intermodulation distortion occurring in a mixer of the receiver, wherein the estimator uses a live transmit signal from the transmitter as reference signal; and

a controller, coupled to the estimator, for adjusting an IIP2 tuning port of the mixer, based on the estimate of second-order intermodulation distortion in the receiver, to reduce second-order intermodulation distortion in the receiver.

2. The IIP2 calibration system of claim 1, wherein the estimator eliminates direct current from a baseband receive signal, while calculating the estimate of second-order intermodulation distortion.

3. The IIP2 calibration system of claim 2, including state machines for configuring the estimator and the controller, the configuring being based on a power output of the transmitter and a received signal strength of the receiver.

4. The IIP2 calibration system of claim 3, wherein a state machine sets a gain of the estimator and a rate of the controller, based on a ratio of transmit power of the transmitter to detected received signal strength of the receiver.

5. The IIP2 calibration system of claim 4, wherein the controller uses a sign-sign least means squared optimization algorithm to estimate the IIP2 coefficients.

6. The IIP2 calibration system of claim 5, wherein the sign-sign least means squared optimization algorithm has a variable step size, the variable step size depending on a magnitude of the IIP2 coefficient estimation.

7. The IIP2 calibration system of claim 6, wherein the receiver is a direct-conversion receiver.

8. The IIP2 calibration system of claim 7, wherein the transmitter transmits simultaneously as the direct-conversion receiver receives.

9. A radio frequency transceiver, comprising:

a duplexer;

a transmitter coupled to the duplexer;

a direct-conversion receiver including a mixer, coupled to the duplexer, wherein the receiver receives a leaked signal comprising a transmit RF signal leaked through the duplexer;

circuitry that determines a transmit power output of the transmitter;

circuitry that determines a received signal strength indication of the receiver;

circuitry that determines a linear gain between baseband of the transmitter and baseband of the receiver; and

a calibration system, including

circuitry, coupled to baseband of the transmitter, that determines a filtered, delayed, amplitude squared version of a baseband transmit signal,

circuitry that multiplies the filtered, delayed, amplitude squared version of a baseband transmit signal with the linear gain to produce a first signal,

circuitry that compares the first signal with a baseband receive signal that includes a second-order intermodulation distortion product produced in the mixer from the leaked signal, wherein the circuitry that compares uses a version of a sign-sign least means squared optimization algorithm for estimating a value of an IIP2 coefficient that is proportional to the second-order intermodulation distortion product produced in the mixer, and

circuitry that produces, in response to results from the optimization algorithm, a tuning voltage for tuning an IIP2 port of the mixer to reduce the second-order intermodulation distortion occurring in the mixer.

10. The radio frequency transceiver of claim 9, wherein the transmitter transmits simultaneously as the direct-conversion receiver receives.

11. The radio frequency transceiver of claim 10, wherein the calibration system includes circuitry that compensates for any DC offset in the baseband receive signal while the calibration system compares the first signal with a baseband receive signal, to reduce degradation of the estimation by the presence of the DC offset.

12. The radio frequency transceiver of claim 11, wherein the circuitry that compensates uses a sign-sign least means squared optimization algorithm to estimate the IIP2 coefficient.

13. The radio frequency transceiver of claim 12, wherein the sign-sign least means squared optimization algorithm has a variable step size, the variable step size depending on a magnitude of the IIP2 coefficient estimation.

14. The radio frequency transceiver of claim 10, wherein the calibration system includes circuitry that compensates only for a certain type of DC offset in the baseband receive signal while comparing the first signal with a baseband receive signal to reduce degradation of the estimation by the presence of the DC offset, the certain type of DC offset being the type of DC offset caused by effects other than second-order intermodulation distortion in the mixer.

15. The radio frequency transceiver of claim 10, in which the radio frequency transceiver is implemented in an integrated circuit.

16. A method of tuning a input-related, second-order intercept point (IIP2) of a mixer in a receiver of a transceiver including a transmitter, comprising the steps of:

determining whether power output of the transmitter is greater than a predetermined power output level F;

determining whether a received signal strength indication of the receiver is less than a predetermined received signal strength indication level H;

providing values for a gain of an IIP2 estimator and an update rate of a IIP2 controller;

using the gain of the IIP2 estimator, performing an optimization algorithm for estimating an estimated value of an IIP2 coefficient that is proportional to second-order intermodulation distortion occurring in the mixer;

using the update rate of the IIP2 controller and the estimated value of the IIP2 coefficient, performing an optimization algorithm for changing a tuning voltage of the mixer;

waiting a period for a change to occur in one or both of the power output level of the transmitter and a received signal strength indication of the receiver;

after waiting the period, determining whether a change in one or both of the gain of the IIP2 estimator and the update rate of the IIP2 controller has occurred;

based upon one of or both the change of the power output level and the received signal strength indication, determining whether a change in one or both of the gain of the IIP2 estimator and the update rate of the IIP2 controller are required; and

if any such change is required, making a change in one or both of the gain of the IIP2 estimator and the update rate of the IIP2 controller, based upon information stored in a look-up table.

17. The method of claim 16, wherein the step of performing the optimization algorithm for estimating the estimated value of the IIP2 coefficient includes a step of compensating for DC offset in the receiver, thereby reducing any degradation of the estimate caused by the presence of the DC offset.

18. The method of claim 17, wherein the values for the gain of the IIP2 estimator and the update rate of the IIP2 controller are obtained from respective look-up tables, based upon the power output of the transmitter and the receiver signal strength indication of the receiver.

19. The method of claim 16, wherein the optimization algorithm is a sign-sign least means squared optimization algorithm.

20. The method of claim 19, wherein the sign-sign least means squared optimization algorithm has a variable step size, the variable step size depending on a magnitude of the IIP2 coefficient estimation.