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 inefficiency due to nonlinearity, leading to spectral regrowth, adjacent channel interference, and increased bit-error-rate, which is 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 by determining and adjusting the time-variant target voltage envelope based on extracted mDPD coefficients, improving linearity and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PAs are configured with a relatively large back-off to operate within a linear portion, then linearity is improved, but power efficiency deteriorates (operating at less than 10% efficiency)
Solution Approach 1:
The voltage mDPD circuit performs preliminary correction on the target voltage envelope before it is applied to the PA. By executing the mDPD polynomial in advance to extract coefficients and adjust the voltage envelope, the system pre-compensates for nonlinearity, allowing the PA to operate at high efficiency without suffering from severe nonlinearity effects
2Use of energy by moving object
If PAs operate at high efficiency without large back-off, then power efficiency is improved, but nonlinearity increases (generating spectral regrowth and adjacent channel interference)
Solution Approach 1:
The voltage mDPD circuit applies preliminary anti-action by pre-distorting the target voltage envelope in the opposite direction of the expected nonlinearity. The circuit executes the mDPD polynomial to calculate correction coefficients that counteract the PA's nonlinearity, thereby preventing spectral regrowth and adjacent channel interference before they occur
3Use of energy by moving object
If envelope tracking is used to improve PA efficiency, then power consumption is reduced, but voltage deviation occurs in the ET modulated voltage
Solution Approach 1:
The voltage mDPD circuit implements feedback by continuously monitoring the target voltage envelope and adjusting it based on extracted mDPD coefficients. The circuit uses the polynomial execution results to feed back corrections to the voltage envelope, compensating for voltage deviation and ensuring accurate voltage tracking while maintaining power efficiency
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.