Power Amplifier Predistortion for Symmetric ACLR Reduction
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Solution Overview
Problem
Power amplifiers in wireless communication devices exhibit nonlinearity, leading to increased error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) values, causing signal distortion and interference in adjacent frequency bands.
Innovation Solution
A wireless communication device with a pre-distortion circuit, measurement circuit, filtering circuit, and pre-distortion coefficient update circuit to adjust frequency components by pre-distorting input signals, measuring adjacent channel magnitudes, and updating coefficients to reduce ACLR values symmetrically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the power amplifier operates nonlinearly to increase efficiency, then power efficiency is improved, but adjacent channel leakage ratio increases causing signal distortion and interference
Solution Approach 1:
The pre-distortion circuit applies preliminary anti-action by pre-distorting the input signal in advance to compensate for the power amplifier's nonlinearity. The pre-distortion coefficient is calculated based on measured adjacent channel leakage, and the pre-distortion signal is generated before amplification to counteract the expected nonlinear effects, thereby reducing ACLR while maintaining power efficiency
Solution Approach 2:
The measurement circuit measures the adjacent channel leakage ratio of the output signal and feeds this information back to the pre-distortion coefficient calculation circuit. This feedback loop enables continuous optimization of the pre-distortion coefficient to minimize ACLR while maintaining high power amplifier efficiency
2Object-generated harmful factors
If pre-distortion circuit is added to compensate for nonlinearity, then adjacent channel leakage ratio is reduced, but device complexity increases
Solution Approach 1:
The processor performs multiple functions including signal generation, pre-distortion coefficient calculation, and ACLR measurement. The same processor also updates the pre-distortion coefficient based on measured ACLR values, consolidating multiple functions into a single component to reduce overall device complexity
Solution Approach 2:
The pre-distortion circuit is integrated with the power amplifier in a combined transmitter architecture. The measurement circuit and pre-distortion coefficient update circuit share the same signal path and processing resources, merging multiple functional blocks to reduce device complexity while maintaining ACLR reduction capability
Data Source
AI summary
A wireless communication device includes a pre-distortion circuit configured to generate a pre-distortion signal by pre-distorting an input signal based on a pre-distortion coefficient, a power amplifier configured to generate an output signal by amplifying the pre-distortion signal, a measurement circuit configured to measure a magnitude of a first frequency component of a first adjacent channel and a magnitude of a second frequency component of a second adjacent channel of the output signal, a filtering circuit, that includes an error filter, configured to generate a filtered error signal by filtering an error signal that is based on the input signal and the output signal, the error filter is configured based on the magnitude of the first frequency component and the magnitude of the second frequency component, and a pre-distortion coefficient update circuit configured to update the pre-distortion coefficient based on the error signal or the filtered error signal.