Voltage Memory Predistortion for ET Amplifier Linearity
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Solution Overview
Problem
Power amplifiers in mobile communication devices, particularly in LTE and 5G-NR systems, face inefficiencies due to nonlinearity, leading to spectral regrowth, adjacent channel interference, and increased bit-error-rate, which are exacerbated by high peak-to-average ratios in RF signals, forcing them to operate with low efficiency and generate excessive thermal heat.
Innovation Solution
A voltage memory digital pre-distortion (mDPD) circuit is introduced in an envelope tracking amplifier circuit to reduce voltage deviation in the ET modulated voltage, improving linearity by adjusting the time-variant target voltage envelope based on extracted mDPD coefficients, thereby enhancing the efficiency and performance of power amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back-off is configured to operate within linear portion of PA, then linearity is improved, but efficiency deteriorates
Solution Approach 1:
The system performs preliminary action by pre-distorting the RF signal before amplification and pre-adjusting the supply voltage envelope to anticipate and compensate for PA nonlinearity effects. This allows the PA to operate in a more efficient region while maintaining linearity through compensatory measures applied in advance.
Solution Approach 2:
The system implements feedback by continuously monitoring the PA output and using this information to adjust the pre-distortion parameters and supply voltage envelope in real-time, enabling dynamic optimization of both linearity and efficiency based on actual operating conditions.
2Power
If back-off is reduced to handle high peak-to-average ratios, then power handling capability is improved, but efficiency deteriorates further
Solution Approach 1:
The envelope tracking system performs preliminary action by pre-adjusting the supply voltage envelope to match the anticipated signal peaks, enabling the PA to deliver high peak power without requiring excessive back-off. This allows efficient operation even when handling high peak-to-average ratio signals.
Solution Approach 2:
The system dynamically changes the supply voltage parameter in real-time to optimize PA operation. By adjusting the supply voltage envelope to match the signal characteristics, the system enables high power handling while maintaining efficiency, avoiding the need for fixed back-off configurations.
3Use of energy by moving object
If envelope tracking is implemented to improve efficiency, then power consumption is reduced, but voltage deviation occurs
Solution Approach 1:
The voltage mDPD circuit implements feedback by continuously monitoring the actual supply voltage and comparing it with the target voltage envelope. This feedback information is used to adjust the ET modulated voltage and compensate for deviations, maintaining voltage accuracy while preserving efficiency benefits.
Solution Approach 2:
The system dynamically adjusts voltage parameters through the mDPD polynomial to compensate for non-ideal effects. By changing the ET modulated voltage based on extracted coefficients, the system corrects voltage deviations while maintaining the efficiency improvements from envelope tracking.
4Reliability
If voltage mDPD circuit is added to reduce voltage deviation, then linearity is improved, but device complexity increases
Solution Approach 1:
The voltage mDPD circuit acts as an intermediary component between the envelope tracker and the power amplifier. It processes the ET modulated voltage through polynomial operations to correct deviations, improving linearity without requiring fundamental redesign of the main PA architecture.
Solution Approach 2:
The system replaces complex hardware-based linearity correction mechanisms with software-based polynomial processing in the voltage mDPD circuit. This computational approach achieves linearity improvement with relatively simple digital processing rather than complex analog circuitry.
Data Source
AI summary
An envelope tracking (ET) amplifier circuit is provided. The voltage mDPD circuit is provided in an ET amplifier circuit and configured to determine a voltage deviation relative to an ET modulated target voltage signal, execute an mDPD polynomial in one or more iterations to extract an mDPD coefficient(s), and adjust a time-variant target voltage envelope of the ET modulated target voltage signal based on the mDPD coefficient(s) extracted in each of the mDPD iterations to reduce the voltage deviation to a predefined threshold. By reducing the voltage deviation in the ET modulated voltage, it is possible improve linearity (e.g., gain linearity) of the ET amplifier circuit, which can lead to reduced power consumption and improved radio frequency (RF) performance.