Quadrature Feedback Mixer Predistortion for PA Distortion Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power amplifier circuits in wireless systems suffer from distortion, leading to signal transmission errors and reduced communication quality due to large swings in output power levels, which are exacerbated by integration with other RF transmitter circuitry and limitations in semiconductor fabrication technologies.
Innovation Solution
A digital predistortion scheme with a quadrature feedback mixer configuration is used to estimate and compensate for amplitude modulation to amplitude modulation (AM-AM) and amplitude modulation to phase modulation (AM-PM) distortions by adjusting input power levels and phases, allowing for improved signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power amplifier circuits are used to transmit output signals at high power levels, then transmission power is improved, but distortion increases leading to signal transmission errors
Solution Approach 1:
The system applies digital predistortion to the input signal before amplification, pre-compensating for the expected nonlinear distortion characteristics of the power amplifier. This preliminary action ensures that the distorted output matches the desired linear output, maintaining signal accuracy at high power levels
Solution Approach 2:
The system employs feedback mixers to capture the actual output signal and compare it with the expected output, using this feedback information to continuously adjust and refine the predistortion parameters, thereby maintaining high transmission accuracy despite power amplifier nonlinearities
2Power
If output power levels are increased to improve communication range, then transmission distance is improved, but distortion performance deteriorates
Solution Approach 1:
The predistortion filter is configured with coefficients that pre-compensate for amplifier nonlinearities before the signal enters the high-power stage, allowing the system to operate at higher power levels without generating excessive distortion
Solution Approach 2:
The system dynamically adjusts the predistortion filter parameters and amplifier operating points to optimize the balance between output power and distortion performance, changing system parameters adaptively based on operating conditions
3Reliability
If digital predistortion is applied to compensate for distortion, then signal accuracy is improved, but device complexity increases
Solution Approach 1:
The feedback mixers and signal processing circuits serve multiple functions: they provide feedback for predistortion adjustment, enable distortion measurement, and support system calibration, thereby reducing the need for separate dedicated circuits and offsetting the added complexity
Solution Approach 2:
The system uses its own output signal through the feedback path to automatically characterize and compensate for its own nonlinearities, eliminating the need for external calibration equipment and reducing overall system complexity
Data Source
AI summary
Aspects of a method and system for compensating for distortion in a transmitter by utilizing a digital predistortion scheme with a feedback mixer configuration are presented. Aspects of the system may include an RF transmitter that enables generation of an RF output signal in response to one or more generated input signals. One or more feedback signals may be generated by performing frequency downconversion on the RF output signal within a corresponding one or more feedback mixer circuits. The generated one or more feedback signals may be inserted at a corresponding one or more insertion points in an RF receiver. Each insertion point may be between a receiver mixer circuit and corresponding circuits that generate a baseband signal based on the corresponding one of the feedback signals.