At&t Bell Laboratories

Lucent Technologies Inc.

Agere Systems Inc.

James P Moffatt

James Russell Blodgett

Michael W Goodwin

Jeffrey H Saunders

Donald R Green, Jr

Gerald L Frazer

Mitchell A Skinner

Karen E Leonard

Fan Zhang

A predistorter is disclosed that predistorts an input signal based on one or more static coefficients that are representative of a non-linear distortion characteristic of an amplifier. The input signal is also processed based on a non-linear gain parameter that reduces an error metric between the input signal and a feedback signal. The nonlinear gain parameter adapts an amount of nonlinearity introduced by the predistorter. The non-linear gain adaptation is performed, for example, when the input voltage is above a threshold input voltage. The input signal can be processed by multiplying the input signal by the non-linear gain parameter followed by table-coefficient processing, or by both multiplying the input by the non-linear gain parameter followed by dividing the table-coefficient processed output signal by the same non-linear gain parameter. The input signal can also be processed based on a feedback gain parameter that compensates for a small-signal gain of the feedback loop. The feedback gain parameter attempts to maintain a small-signal gain of approximately unity.

Method and apparatus for adaptive digital predistortion using nonlinear and feedback gain parameters

An adaptive controller generates a sequence of dither signals for each of a plurality of control parameters. Each dither signal sequence is uncorrelated with every other dither signal sequence. Each nominal control signal has the first of its respective dither signal values simultaneously summed with it to form the control parameter values used by the controller. Updated control signals are applied in parallel to the controller outputs and a performance measure is taken and stored. The second signals in the dither control sequences are then summed with their respective nominal controls and applied in parallel to the controller and a second performance measure is taken and stored. This process is repeated for the length of the dither control signal sequence to yield a sequence of performance measurements. The sequence of performance measurements is correlated with each of the dither sequences, forming sequences of correlator outputs, one for each control signal. Each correlator output sequence is integrated and, depending upon the value of a correlator's integration output, the corresponding nominal signal has it's dither value added to or subtracted from it to form the respective, updated control values.

Apparatus and method for adaptive control

Characterized nonlinearities in a QAM transmission channel are removed by this linearizer, in which selected bits from a sequence of received symbols on both rails form the address of a PROM. Stored values represent the Volterra expansion of the response of the channel, including the nonlinearity, to the symbol sequence. Symmetries in the Volterra expansion allow the same stored value to be used to correct both AM/AM same rail and AM/PM opposite rail distortion.

Volterra linearizer for digital transmission

Amplifier-produced distortion known as amplitude modulation to phase modulation (AM/PM) conversion is reduced through the use of GaAs FETs which are biased to generate AM/PM having an algebraic sign opposite to that generated by the amplifier. This algebraic sign reversal is accomplished by biasing the GaAs FETs so that a DC drain current .ltoreq.75% and .gtoreq.10% of the short-circuit drain current is established. In the disclosed embodiment, several GaAs FETs are cascaded in alternation with attenuators to increase the magnitude of the compensating AM/PM conversion without generating substantial amplitude modulation to amplitude modulation (AM/PM) conversion.

Distortion compensation for a microwave amplifier

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Salem, NH, United States of America

James P Moffatt