US 7,215,716 B1Granted

Non-linear adaptive AM/AM and AM/PM pre-distortion compensation with time and temperature compensation for low power applications

AssigneeFrancis J. Smith

InventorFrancis James Smith

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Abstract

This invention provides a technique and an architecture to pre-distort signals such that when the signals are amplified, the non-linear distortions of the amplifier chain are opposite that of the pre-distortion thus yielding a distortion free or nearly distortion free signal at the output of the amplifier chain. This invention provides for a low power application by using a LUT predistortion that is performed on a composite real signal (I and Q combined) such that the size of the LUTs required is reduced to a very small size. In this invention, the I and Q input signals are digitally modulation with quadrature digital sinusoidal signals and then combined to create the real composite signal at a digital IF. The real signal is then pre-distorted to compensate for AM/AM distortion first and then for AM/PM distortion. The pre-distorted signal is then digitally decomposed back in to I and Q samples for conversion to analog and up conversion to RF. The non-pre-distorted real signal is sampled and compared with a sample of the post amplified signal and the non-linear update algorithm is updated to compensate for the variation of non-linear distortion as a function of time and temperature. The architecture and techniques described herein provide for a low power and low memory implementation that can be used in mobile applications such as cell phones and Personal Data Devices (PDAs).

Claims40

Dependent claims

A method comprising:

a pre-distortion of a signal which will be subjected to a non-linear channel wherein the signal will be distorted by the non-linear characteristic of the channel and the pre-distortion will induce the opposite distortion to that of the channel;
a method wherein the signal will be converted from a complex I and Q baseband signal to a digital IF composite real signal and the AM/AM and AM/PM pre-distortion is performed on the real composite signal;
a method wherein the pre-distorted signal is converted back to a complex I and Q form and the I and Q channels are individually converted to a baseband analog form and then the compound real signal is created at RF after the complex up conversion to RF;
a method wherein the post amplified signal is sampled and is compared to the non-pre-distorted compound real signal to determine the error in the AM/AM and AM/PM pre-distortion algorithm;
a method wherein the non-linear pre-distortion algorithm is updated with the data from the comparison of the pre-distorted post amplified signal and the non-pre-distorted signals;
a method wherein the AM/AM and AM/PM pre-distortion LUTs are dual memories wherein one is updated while the other is used and then they are switched in one symbol time so no data is lost in the algorithm update process;
a method where in the AM/PM pre distortion is done digitally;
a method where in the AM/PM pre-distortion is done via an analog technique;
a method wherein the non-linear pre-distortion algorithm is computed by computing a series model of the non-linear channel by computing a series from the sampled values of the post amplified pre-distorted signal.

6 more elements

An apparatus comprising:

a pre-distortion of a signal which will be subjected to a non-linear channel wherein the signal will be distorted by the non-linear characteristic of the channel and the pre-distortion will induce the opposite distortion to that of the channel;
a method wherein the signal will be converted from a complex I and Q baseband signal to a digital IF composite real signal and the AM/AM and AM/PM pre-distortion is performed on the real composite signal;
a method wherein the pre-distorted signal is converted back to a complex I and Q form and the I and Q channels are individually converted to a baseband analog form and then the compound real signal is created at RF after the complex up conversion to RF;
a method wherein the post amplified signal is sampled and is compared to the non-pre-distorted compound real signal to determine the error in the AM/AM and AM/PM pre-distortion algorithm;
a method wherein the non-linear pre-distortion algorithm is updated with the data from the comparison of the pre-distorted post amplified signal and the non-pre-distorted signals;
a method wherein the AM/AM and AM/PM pre-distortion LUTs are dual memories wherein one is updated while the other is used and then they are switched in one symbol time so no data is lost in the algorithm update process;
a method where in the AM/PM pre distortion is done digitally;
a method where in the AM/PM pre-distortion is done via an analog technique;
a method wherein the non-linear pre-distortion algorithm is computed by computing a series model of the non-linear channel by computing a series from the sampled values of the post amplified pre-distorted signal.

6 more elements

Dependencies are inferred from the claim text.