Pre-Distortion Power Control for Linear RF Amplifier Output
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Solution Overview
Problem
Amplifiers in wireless communication devices face variability in output power due to manufacturing process variations, power supply voltage, temperature, frequency, and load impedance, leading to non-linear signal relationships and challenges in achieving target power outputs while maintaining signal quality metrics like ACLR and EVM.
Innovation Solution
A pre-distortion circuit is coupled with the amplifier to generate a pre-distortion input signal that compensates for the amplifier's non-linearities, determining an input target value based on the saturation value and controlling the average or RMS value of the input signal to achieve a linear relationship between input and output signals, thereby stabilizing the output power and signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amplifier operates at high power output, then the productivity is improved, but the manufacturing precision deteriorates due to non-linear operation and process variations
Solution Approach 1:
The pre-distortion circuit applies preliminary correction to the input signal before amplification, pre-compensating for the amplifier's non-linear characteristics. This allows the amplifier to operate at high power while maintaining signal linearity, as the non-linearities are counteracted by the pre-applied distortion correction
Solution Approach 2:
The system measures actual output signal characteristics and uses this feedback to adjust the pre-distortion parameters, creating a closed-loop control system that maintains optimal linearity across varying operating conditions and manufacturing variations
2Adaptability or versatility
If the amplifier operates under varying conditions (temperature, voltage, frequency), then the adaptability is improved, but the stability of output power deteriorates
Solution Approach 1:
The pre-distortion parameters are made dynamic rather than fixed, allowing the system to adapt to changing temperature, voltage, and frequency conditions. The parameters are adjusted in real-time based on measured operating conditions, maintaining stable output power across varying environments
Solution Approach 2:
The system continuously monitors operating conditions and output power, using feedback to adjust pre-distortion parameters and maintain stable output power despite variations in temperature, voltage, or frequency
3Use of energy by moving object
If the amplifier operates in non-linear fashion, then the power efficiency is improved, but the signal quality deteriorates
Solution Approach 1:
The pre-distortion circuit pre-compensates for the non-linearities that will occur during amplification, allowing the amplifier to operate in an efficient non-linear region while the output signal remains linear and high-quality due to the pre-applied correction
Data Source
AI summary
An apparatus comprises an amplifier and a pre-distortion circuit coupled to an input of the amplifier. A saturation value of an input signal corresponds to a maximum output power of an output signal of the amplifier. An input target value of the input signal is determined according to the saturation value. The input target value is determined by subtracting an offset from the saturation value or by multiplying a ratio by the saturation value. An average value or an RMS value of the input signal is controlled to be substantially equal to the input target value. A method comprises determining an input target value according to a saturation value, and controlling an input signal according to the input target value.