Adaptive digital pre-distortion using amplifier model that incorporates frequency-dependent non-linearities
AssigneeAndrew Corporation
InventorRajiv Chandrasekaran
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Abstract
A pre-distorter pre-distorts an input signal prior to being applied to an amplifier in order to reduce spurious emissions in the resulting amplified signal. The pre-distorter implements an inverted version of a model of the amplifier that models both the frequency independent (FI) characteristics of the amplifier as well as the frequency-independent (FD) characteristics of the amplifier. Techniques and architectures are presented for (1) generating and updating the model, (2) inverting the model, and (3) updating the inverted model.
Claims40
A method for pre-distorting a signal for amplification, the method comprising the steps of:
- (a) receiving an input signal;
- and
- (b) applying pre-distortion to the input signal to generate a pre-distorted signal, such that, when the pre-distorted signal is applied to an amplifier to generate an amplified signal, the pre-distortion reduces spurious emissions in the amplified signal, wherein:
- the pre-distortion is generated using an inverse of a model of the amplifier;
- and
- the model comprises a model of frequency-independent (FI) characteristics of the amplifier (an FI model) in combination with a model of frequency-dependent (FD) characteristics of the amplifier (an FD model).
An apparatus for pre-distorting a signal for amplification, wherein the apparatus is configured to:
- (a) receive an input signal;
- and
- (b) apply pre-distortion to the input signal to generate a pre-distorted signal, such that, when the pre-distorted signal is applied to an amplifier to generate an amplified signal, the pre-distortion reduces spurious emissions in the amplified signal, wherein:
- the pre-distortion is generated using an inverse of a model of the amplifier, and the model comprises an FI model of frequency-independent characteristics of the amplifier in combination with an FD model of frequency-dependent characteristics of the amplifier.
An apparatus for pre-distorting a signal for amplification, the apparatus comprising:
- (a) One or more high-order transfer function elements, each configured to apply a transfer function of a different order greater than one to a corresponding distortion product for an input signal;
- (b) a summation node configured to sum the input signal and the output of each high-order transfer function element;
- (c) an inverted transfer function element configured to apply an inverted first-order transfer function to the output of the summation node;
- and
- (d) an inverted FI element configured to apply an inverse of a model of a frequency-independent (FI) gain of the amplifier to the output of the inverted transfer function element to generate a pre-distorted signal, such that, when the pre-distorted signal is applied to an amplifier to generate an amplified signal, spurious emissions in the amplified signal are reduced.
A method for generating a model of an amplifier, wherein the model comprises an FI model of frequency-independent characteristics of the amplifier in combination with an FD model of frequency-dependent characteristics of the amplifier, wherein the model is generated by estimating a plurality of transfer functions for the FD model in a sequence corresponding to increasing order of the transfer function.
A method for adaptively updating a pre-distorter configured to pre-distort an input signal for application to an amplifier configured to generate an amplified signal, the pre-distorter comprising at least one look-up table (LUT), wherein the at least one LUT is adaptively updated by minimizing an error between the input signal and a feedback signal based on the amplified signal, wherein the at least one look-un table is undated by applying a recursive estimation technique to the at least one look-up table.
Dependencies are inferred from the claim text.