Linearization of a transmit amplifier
First Claim
1. A method of linearization of a transmit amplifier, said method comprising the steps of:
- scanning a plurality of power amplifier codes;
generating a transmit amplifier output signal in accordance with each code scanned; and
determining one or more predistortion values in accordance with said transmit amplifier output signal; and
wherein said step of determining comprises the step of inputting said transmit amplifier output signal to an on-chip receiver chain operative to generate I and Q samples therefrom.
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Accused Products
Abstract
A novel apparatus and method of linearization of a digitally controlled pre-power amplifier (DPA) and RF power amplifier (PA). The mechanism is operative to perform predistortion calibration to compensate for nonlinearities in the DPA and PA circuits. A predistortion look up table (LUT) stores measured distortion compensation data that is applied to the TX data before being input to the digital to frequency converter (DFC), DPA and PA. The mechanism of the invention takes advantage of the on-chip receiver, which is normally inactive during the TX burst in a half-duplex operation, to demodulate the RF PA output and use the digital I/Q RX outputs to perform calibration of the TX pre-distortion tables. Controlled RF coupling is used to provide a sample of the RF output signal that to the receiver chain. The contents of the predistortion LUT are typically updated during the PA power up or down ramp. While the digitally-controlled PA (DPA) code is increasing (or decreasing), the amplitude and phase of the recovered I/Q samples are used to determine the instantaneous value of the AM/AM and AM/PM pre-distortion from which an update to the predistortion tables may be computed.
109 Citations
38 Claims
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1. A method of linearization of a transmit amplifier, said method comprising the steps of:
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scanning a plurality of power amplifier codes; generating a transmit amplifier output signal in accordance with each code scanned; and determining one or more predistortion values in accordance with said transmit amplifier output signal; and wherein said step of determining comprises the step of inputting said transmit amplifier output signal to an on-chip receiver chain operative to generate I and Q samples therefrom. - View Dependent Claims (2, 3, 4, 5)
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6. A method of compensating for predistortion of a transmit amplifier, said method comprising the steps of:
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scanning a plurality of transmit amplifier codes; generating a transmit amplifier output signal in accordance with each code scanned; providing controlled leakage of said transmit amplifier output signal to a receiver chain operative to demodulate said transmit amplifier output signal to yield I and Q samples therefrom; calculating amplitude and phase distortion values in accordance with said I and Q samples; and calibrating a predistortion table with said amplitude and phase distortion values. - View Dependent Claims (7, 8, 9, 10, 11, 12)
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13. A method of predistortion calibration of a transmit amplifier, said method comprising the steps of:
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stepping through a dynamic range of codes of said transmit amplifier; inputting each code to a transmit chain comprising a predistortion look up table (LUT) of transmit amplifier predistortion values to generate a radio frequency (RF) output signal in response thereto; demodulating said RF output signal to recover I and Q samples therefrom; calculating an instantaneous correction to the predistortion values stored in said predistortion LUT in accordance with said recovered I and Q values; and updating the contents of said predistortion LUT in accordance with said calculated instantaneous correction. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. An apparatus for calibrating predistortion of a digitally controlled pre-power amplifier (DPA) and power amplifier (PA), comprising:
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circuitry for stepping through a range of codes of said DPA; a transmit chain comprising a predistortion look up table (LUT) adapted to store a plurality of amplifier predistortion values, said transmit chain operative to generate a radio frequency (RF) output signal in response to each code; circuitry for coupling said RF output signal to a receiver chain, said receive chain operative to demodulate said RF output signal to generate recovered I and Q samples therefrom; circuitry for calculating corrections to the predistortion values stored in said predistortion LUT in accordance with said recovered I and Q values; and update circuitry for updating the contents of said predistortion LUT in accordance with said calculated corrections. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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Specification