RF Power Amplifier Linearity Control Under Varying VSWR
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Solution Overview
Problem
In wireless and cellular applications, power amplifiers face challenges with unstable impedance causing signal reflections, leading to non-linearity issues, particularly in multi-band applications where isolators are undesirable due to size and cost constraints.
Innovation Solution
A method using a digital signal processor (DSP) to measure and control the peak-to-average power ratio of the output signal, adjusting the input drive to maintain an ideal ratio and reduce distortion, which can be implemented with a single or dual detector system and analog-to-digital converters, and optionally a microcontroller for faster processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolator is used between the power amplifier and antenna, then signal linearity is improved by reducing reflections, but device size and cost increase
Solution Approach 1:
The patent extracts the isolator component from the system and replaces it with a digital signal processing approach. The DSP measures the output signal characteristics and adjusts the input drive accordingly, eliminating the need for physical isolation hardware while maintaining signal linearity under varying VSWR conditions
Solution Approach 2:
The patent replaces the mechanical/electrical isolator with a digital signal processing system. The DSP performs measurements and calculations in the digital domain to compensate for reflections, substituting a software-based solution for hardware-based isolation and reducing overall device complexity
2Reliability
If an isolator is used between the power amplifier and antenna, then signal linearity is improved by reducing reflections, but manufacturing cost increases
Solution Approach 1:
The patent removes the isolator component from the bill of materials and replaces it with DSP functionality. This extraction eliminates the cost of purchasing and integrating isolator hardware while maintaining signal linearity through digital measurement and control of the power amplifier output
Solution Approach 2:
The patent uses software-based DSP processing instead of expensive hardware isolators. The digital signal processing approach incurs minimal additional cost beyond the DSP resource itself, providing a cost-effective solution for maintaining signal linearity across multiple frequency bands
3Reliability
If hybrid couplers are used to combine power amplifiers, then sensitivity to load mismatch is reduced, but device complexity and cost increase
Solution Approach 1:
The patent implements a feedback mechanism where the DSP continuously measures the output signal characteristics and uses this information to adjust the input drive to the power amplifier. This closed-loop control reduces sensitivity to load mismatch without requiring additional hardware components like hybrid couplers
Solution Approach 2:
The power amplifier system performs its own optimization through the DSP, which autonomously measures output conditions and adjusts input parameters accordingly. This self-service approach eliminates the need for external matching networks or complex hardware configurations
Data Source
AI summary
The peak-to-average power ratio at the output of an rf power amplifier is detected and compared with, for instance, an ideal ratio. The result of this comparison is used to control the amplifier, particularly to reduce distortion in the output signal.