Adaptive Polar Transmitter Predistortion for Amplifier Linearization
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Solution Overview
Problem
Existing wireless transmitters, particularly those in cellular communication systems like WCDMA, face challenges in achieving linear signal amplification without excessive power consumption and cost, as highly linear amplifiers are power-intensive and costly, while simple nonlinear amplifiers distort signals, and factory-calibrated predistortion lookup tables fail to adequately linearize amplifiers under varying operational conditions.
Innovation Solution
A polar transmitter with a predistorter employing first amplitude and phase compensation lookup tables, coupled with a receiver that updates second amplitude and phase compensation lookup tables based on signal feedback, using an iterative adaptation algorithm to continuously adjust predistortion and improve linearization, especially under changing conditions like temperature and frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If highly linear amplifiers are used to minimize signal distortion, then signal quality is improved, but power consumption and cost increase
Solution Approach 1:
The predistorter applies preliminary distortion to the input signal before it reaches the amplifier, so that the amplifier's nonlinear distortion cancels out the predistortion. This allows the use of simpler, less power-consuming amplifiers while achieving linear output through the combined predistorter-amplifier system.
Solution Approach 2:
The predistorter acts as an intermediary component between the signal source and the amplifier. It pre-processes the signal with inverse distortion characteristics, enabling the amplifier to operate in a more efficient region while maintaining overall signal linearity.
2Manufacturing precision
If factory-calibrated predistortion lookup tables are used, then initial linearization is achieved, but performance degrades under varying operational conditions
Solution Approach 1:
The system uses feedback from the amplifier output to continuously monitor actual distortion characteristics. This feedback signal is used to dynamically update the lookup tables, ensuring the predistorter remains accurate despite changes in temperature, frequency, or other operational conditions.
Solution Approach 2:
The lookup tables transition from static factory-calibrated values to dynamic, adaptively updated values. The system continuously adjusts the predistortion parameters based on real-time operational conditions, making the linearization process adaptive rather than fixed.
3Ease of manufacture
If simple nonlinear amplifiers are used to reduce cost and power consumption, then device simplicity is improved, but signal distortion increases
Solution Approach 1:
The predistorter applies preliminary distortion that is the inverse of the amplifier's nonlinear distortion. This preliminary anti-action cancels out the harmful distortion effects when the signal passes through the amplifier, enabling the use of simple nonlinear amplifiers while maintaining signal linearity.
Data Source
AI summary
A polar transmitter and a method of linearizing a polar transmitter. In one embodiment, the transmitter includes: (1) a transmit chain having a predistorter configured to employ first amplitude and phase compensation lookup tables to carry out predistortion in the transmit chain, (2) a receiver coupled to the transmit chain and (3) predistortion compensation circuitry associated with the receiver and configured to update second amplitude and phase compensation lookup tables associated therewith based on at least one signal from the transmit chain, the values in the updated second amplitude and phase compensation lookup tables thereby available for subsequent predistortion.