RF Front End Linearity Compensation Under VSWR Mismatch
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Solution Overview
Problem
Mobile device front end modules experience performance degradation due to degraded linearity, particularly in envelope tracking (ET) mode with high modulation bandwidth, exacerbated by duplexer-induced memory effects and impedance mismatch, which current memory-less digital pre-distortion (DPD) methods are insufficient to address.
Innovation Solution
A power amplifier system that includes a modulator, a front end module with a power amplifier, a coupler, and a processor that adjusts the RF transmit signal based on voltage standing wave ratio (VSWR) measurements using an equalizer table to compensate for memory effects and impedance mismatch, incorporating a programmable antenna tuner for impedance tuning and fine correction of non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If memory-less digital pre-distortion (DPD) is used to correct power amplifier non-linearity, then some linearity improvement is achieved, but it is insufficient to address memory effects caused by duplexer group delay and impedance mismatch
Solution Approach 1:
The patent transitions from static memory-less DPD to dynamic memory-aware DPD that adapts to varying operating conditions. The system dynamically adjusts pre-distortion parameters based on detected VSWR conditions and signal characteristics, enabling the DPD to compensate for time-varying memory effects caused by duplexer group delay and impedance mismatch variations.
Solution Approach 2:
The patent implements feedback mechanisms where the system continuously monitors VSWR conditions and signal characteristics, then uses this information to adjust the DPD parameters. This closed-loop approach enables the system to adaptively compensate for memory effects that vary with operating conditions, significantly improving linearity under mismatch scenarios compared to open-loop memory-less DPD.
2Use of energy by moving object
If envelope tracking (ET) mode is used to improve power efficiency, then power consumption is reduced, but linearity degradation is exacerbated due to memory effects and impedance mismatch
Solution Approach 1:
The patent applies pre-distortion to the RF signal before amplification to pre-compensate for anticipated memory effects and non-linearities. By calculating and applying the inverse of the expected distortion in advance, the system maintains linearity throughout the power amplification process, enabling ET mode operation without suffering from the typical linearity degradation caused by impedance mismatch and duplexer memory effects.
Data Source
AI summary
A power amplifier system front end measures both forward and reverse power associated with an RF transmit signal. A processor is configured to use measurements derived from the measured forward and reverse power output to adjust the RF transmit signal in order to compensate for one or more memory effects of the power amplifier system.