Analog Predistortion Circuit for Supply-Voltage PA Linearization
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Solution Overview
Problem
Power amplifiers in mobile communication devices face challenges in maintaining linear operation at high frequencies due to varying supply voltages, leading to inefficiencies and increased burden on baseband processors with multiple sets of digital predistortion coefficients.
Innovation Solution
Implementing a supply voltage based analog predistortion (APD) circuit within the amplifier chain to normalize distortion profiles, allowing the baseband processor to use a simplified set of predistortion coefficients by adjusting bias signals and modulating operation with varactors, thereby reducing the need for multiple sets of coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital predistortion uses multiple sets of coefficients to compensate for supply voltage variations, then linear operation is maintained, but baseband processor complexity and memory requirements increase
Solution Approach 1:
An intermediate analog predistortion circuit is introduced between the baseband processor and power amplifier. This circuit receives a single set of simplified coefficients from the baseband processor and generates multiple coefficient sets dynamically based on detected supply voltage levels, thereby maintaining linear operation without burdening the baseband processor with multiple coefficient sets
Solution Approach 2:
The patent replaces the digital mechanism of storing and switching between multiple coefficient sets in the baseband processor with an analog mechanism that dynamically generates appropriate coefficients through voltage detection and analog circuitry, reducing digital processing complexity
2Manufacturing precision
If multiple sets of digital predistortion coefficients are stored for different supply voltages, then distortion compensation is improved, but memory requirements and latency increase
Solution Approach 1:
Instead of storing multiple discrete coefficient sets in memory, the system changes the operating parameter of an analog circuit (the predistortion characteristics) based on the detected supply voltage level. The analog circuit dynamically adjusts its transfer function to provide appropriate predistortion for each voltage condition without requiring stored coefficient data
3Use of energy by moving object
If supply voltage varies to optimize power efficiency, then energy consumption is reduced, but distortion profile changes requiring complex predistortion
Solution Approach 1:
The patent implements a dynamic predistortion system where the analog circuit automatically adapts its characteristics in real-time based on the supply voltage level. When the supply voltage changes to optimize power efficiency, the analog predistortion circuit dynamically adjusts its parameters through voltage detection and automatic gain control, maintaining linear operation without requiring complex digital reconfiguration
Data Source
AI summary
A supply voltage based analog predistortion (APD) circuit for a power amplifier is disclosed. In an exemplary aspect, the power amplifier is in a front end module (FEM) of a radio frequency (RF) transceiver. An APD circuit operates within an amplifier chain to normalize the distortion profile of the amplifier chain based on a supply voltage. A baseband processor (BBP) performs digital predistortion (DPD) on signals being sent from the BBP to the FEM. As a result of the APD circuit, the DPD may assume a normalized profile for the FEM, allowing for simplification of the DPD despite many possible distortions introduced by the amplifier chain based on the supply voltage.