Memory Predistortion for Bandwidth-Limited Envelope Tracking
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Solution Overview
Problem
Envelope tracking systems face challenges with bandwidth limitations, leading to PA efficiency degradation and signal nonlinearities in next-generation cellular technology standards like 5G NR, due to high peak-to-average-power ratio (PAPR) modulation schemes, which result in low PA efficiency, high battery consumption, and excessive heat dissipation in mobile devices.
Innovation Solution
A multi-feed predistorter circuitry is introduced to overcome bandwidth limitations by using a scaled replica of the instantaneous PA power supply voltage and a model distortion signal to compensate for impairments, employing memory polynomial operations to adjust the PA gain compression point and maintain constant gain conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking is used to increase PA efficiency, then power consumption is reduced, but bandwidth limitations cause signal nonlinearities and efficiency degradation
Solution Approach 1:
The predistorter applies memory polynomial operations to pre-compensate the baseband signal before it reaches the PA. By calculating predistortion coefficients based on historical signal data and applying them in advance, the system counteracts the nonlinear effects that will occur during PA operation, thereby maintaining signal linearity while preserving the power efficiency benefits of envelope tracking
Solution Approach 2:
The system continuously monitors the PA output signal and uses this feedback to adjust the predistortion coefficients in real-time. This closed-loop approach ensures that the predistortion accurately compensates for the nonlinearities introduced by the bandwidth-limited envelope tracking, maintaining signal integrity across varying operating conditions
2Productivity
If high PAPR modulation schemes are used to meet 5G NR requirements, then data transmission capability is improved, but PA efficiency decreases leading to high battery consumption
Solution Approach 1:
The system dynamically adjusts the predistortion parameters and PA operating points based on the instantaneous signal conditions and envelope characteristics. By adapting these parameters in real-time, the system maintains optimal PA efficiency across the wide dynamic range required for high PAPR modulation schemes, thereby reducing battery consumption while preserving data transmission capability
3Device complexity
If envelope tracking bandwidth is limited, then device complexity is reduced, but PA efficiency degradation occurs due to inability to track fast envelope variations
Solution Approach 1:
The predistorter acts as an intermediary between the baseband signal and the PA, pre-compensating for the bandwidth limitations of the envelope tracking system. By applying memory polynomial operations that account for the tracker's bandwidth constraints, the system recovers the PA efficiency that would otherwise be lost due to the inability to track fast envelope variations, all while maintaining the simplicity of the bandwidth-limited tracker architecture
Data Source
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AI summary
An apparatus compensates nonlinearities in envelope tracking (ET) used in a mobile device by limiting a bandwidth of an envelope signal representing an envelope of an input baseband signal to be less than a bandwidth of tracker circuitry, generating a scaled replica of an output signal of the tracker circuitry based on the bandwidth-limited envelope signal, and generating a model distortion signal based on the scaled replica and the input baseband signal, where the model distortion signal emulates ET linearity degradation. The apparatus is further configured to generate an output baseband signal based on the scaled replica, the model distortion signal, and the input baseband signal, where the output baseband signal is pre-distorted relative to the input baseband signal according to the scaled replica, the model distortion signal, and the input baseband signal to compensate for degradations in transmit signal quality due to ET nonlinearities.