High efficiency linearization power amplifier for wireless communication
An embodiment of the invention uses a predistortion correction signal to combination the modulated RF signal by an analog multiplier for linearization of power amplifiers having nonlinear characteristics such as those used in wireless RF transmitters. A predistortion controller comprises a plurality of down converters for retrieving both the ideal non-distorted information and the feedback distorted information, together with pre-stored digitally-indexed predistortion information stored, for example, in a look-up table. The digitally-indexed information models nonlinear characteristics of the high power amplifier, and is stored prior to processing of pre-compensation in the power amplifier. When the predistortion information is combined with the modulated RF signal in the analog multiplier, the result is a substantially linear information transmission from the power amplifier. In an embodiment of the system, the modulated RF input signal and the feedback signal from PA output are down-converted, respectively, by analog devices, such as mixers, after which the analog intermediate frequency (IF) signals are digitized by analog-to-digital converters for digital predistortion correction processing, followed by predistortion processing performed by, for example, a DSP or FPGA chip to generate a digital correction control signal, which is then converted to an analog signal by a digital-to-analog converter, followed by combining the analog correction signal with the RF modulated input signal to yield the input to the power amplifier.
1. A predistortion system for linearizing the output of a power amplifier comprising
a first signal representative of an RF modulated signal,
a first A-to-D converter responsive to the first signal for generating a first quadrature signal representative of the first signal,
a feedback signal representative of nonlinear characteristics of a power amplifier,
a second A-to-D converter responsive to the feedback signal for generating a feedback quadrature signal,
a predistortion controller, comprising at least one lookup table, adapted to receive the first quadrature signal and the feedback quadrature signal, to square the respective quadrature signals, and to generate a correction factor for correcting the nonlinear characteristics of the power amplifier, and
combining logic which combines the RF modulated signal with a signal corresponding to the correction factor and supplies it to the power amplifier to linearize the output of the power amplifier.
2. The predistortion system of claim 1 wherein the combining logic is an analog multiplier.
3. The predistortion system of claim 1 wherein the predistortion controller comprises error logic that determines the error between the first signal and the feedback signal.
4. The predistortion system of claim 1 wherein the predistortion controller further includes an address former responsive to the first signal for generating an address supplied to the at least one look-up table.
5. A predistortion system for use with power amplifiers for wireless applications comprising
an analog multiplier,
a first I/Q signal representative of a first input signal,
a feedback I/Q signal representative of nonlinear characteristics of a power amplifer,
at least one error detector for comparing the square of the first I/Q signal and the square of the feedback I/Q signal,
an address former responsive to the first I/Q signal for forming an address,
at least one lookup table responsive to the address and to a second input,
at least one mixer for combining an output of the at least one lookup table with an output of the error detector, the output of the mixer providing the second input to the lookup table,
the output of the lookup table forming one input to the analog multiplier and the first input signal forming a second input to the analog multiplier, and an output of the analog multiplier providing an inversely matching input to the power amplifier for linearizing the output of the power amplifier.
6. The predistortion system of claim 5 wherein the at least one lookup table is at least two lookup tables.
7. The predistortion system of claim 6 wherein one of the at least two lookup tables stores I data and another of the at least two lookup tables stores Q data.