RF Power Amplifier Linearization Using Feedback and Feedforward
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Solution Overview
Problem
Current radio frequency power amplifier linearization techniques face challenges such as sensitivity to drift, stability issues, limited bandwidth, and increased circuit complexity and power dissipation, particularly in high-bandwidth applications like 802.11ac wireless communication standards.
Innovation Solution
A radio frequency power amplifier system incorporating a main amplifier and two auxiliary amplifiers with a feedback network and a feedforward amplifier, where the auxiliary amplifiers are replicas of each other with different gains, and the feedforward network is used to isolate and amplify deviations from the ideal response, allowing for indirect feedback and improved linearization over a wider frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-distortion technique is used to linearize the power amplifier output signal, then the linearity of the output signal is improved, but the system becomes sensitive to drift and requires initial calibration
Solution Approach 1:
The patent implements a feedback network that taps a portion of the output signal from the first auxiliary amplifier and feeds it back to the input of the same amplifier. This feedback mechanism continuously corrects for drift and maintains linearity without requiring external calibration, thereby resolving the contradiction between achieving high linearity and maintaining reliability against drift
Solution Approach 2:
The first auxiliary amplifier with feedback network operates autonomously to generate a linearized version of the input signal. By self-correcting through its own output feedback, the system eliminates the need for external calibration and training procedures, making the system self-sufficient and drift-resistant
2Reliability
If Cartesian feedback system is used to linearize the power amplifier, then drift issues are eliminated, but stability problems and limited bandwidth occur
Solution Approach 1:
The patent divides the amplification function into multiple independent auxiliary amplifiers (first and second auxiliary amplifiers) with different gain values, rather than using a single feedback loop. Each auxiliary amplifier processes the signal independently with feedback, avoiding the stability issues associated with wideband Cartesian feedback while maintaining drift elimination benefits
Solution Approach 2:
Each auxiliary amplifier is equipped with its own localized feedback network tailored to its specific gain characteristics. The first auxiliary amplifier has feedback optimized for its gain value, and the second auxiliary amplifier has feedback optimized for its different gain value, allowing each to operate stably in its own bandwidth range
3Manufacturing precision
If linear feedback is used to linearize the power amplifier, then superior linearization performance is achieved, but the system becomes difficult to stabilize under different load conditions
Solution Approach 1:
The patent uses multiple auxiliary amplifiers with different gain values that can be dynamically selected or combined based on operating conditions. The system adapts to different load conditions by utilizing the appropriate auxiliary amplifier, maintaining both high linearization performance and stability across varying loads
4Manufacturing precision
If feedback network is added to linearize the power amplifier output, then the linearity is improved, but circuit complexity and power dissipation increase
Solution Approach 1:
The auxiliary amplifiers serve multiple functions: they provide signal amplification, generate linearized versions of the input signal through their respective feedback networks, and contribute to the overall output signal composition. This multi-functionality reduces the need for separate dedicated linearization circuits, thereby limiting the increase in circuit complexity
Data Source
AI summary
The present disclosure relates to a radio frequency power amplifier system (200) comprising a first (114) and a second input port (121). The radio frequency power amplifier system (200) comprises a main amplifier (101) having an input (107) and an output (108) and a first (102) and a second auxiliary amplifier (122) having respective inputs (109, 129) and outputs (110, 128). The radio frequency power amplifier system (200) comprises an internal load (103) connected to the output (110) of the first auxiliary amplifier (102), a feedback network (104) having an input end (111) connected to the output (110) of the first auxiliary amplifier (102) and an output end (112) connected to the input (109) of the first auxiliary amplifier (102). The radio frequency power amplifier system (200) also comprises a feedforward amplifier (123) having an input (124) and an output (130). The inputs (107, 129, 109) of the main amplifier and the auxiliary amplifiers are interconnected with the first input port (114) at a common input node (113), the output (128) of the second auxiliary amplifier (122) and the second input port (121) are interconnected with the input (124) of the feedforward amplifier (123) at a common node (127) and the outputs (130,108) of the feedforward amplifier (123) and the main amplifier (101) are interconnected at a common output node (125). The main amplifier (101) is a replica of the first auxiliary amplifier (102) with an increased gain and the second auxiliary amplifier (122) is a replica of the first auxiliary amplifier (102).