Cartesian Error Feedback Circuit for Power Amplifier Distortion
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Solution Overview
Problem
Existing microwave amplifier technologies face inefficiencies, limited bandwidth, complexity, and limited effectiveness in distortion correction, particularly in high-efficiency non-linear amplifiers used in wireless devices, due to the limitations of classical techniques such as feed-forward, pre-distortion, adaptive bias, synthesis, feedback, and other methods.
Innovation Solution
A method involving a microwave processor that divides input signals into primary and secondary components, uses a vector modulator to form an RF signal, amplifies it, and then uses vector demodulation and summation circuits to generate an error feedback signal, which is used to reduce distortion in the output signal, thereby enhancing amplification efficiency and correcting distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If non-linear amplifier classes (C, D, E, F) are used to achieve high efficiency (>90%), then power efficiency is improved, but distortion is generated requiring complex correction techniques
Solution Approach 1:
The patent implements Cartesian feedback by tapping a portion of the amplifier output, down-converting it to baseband, comparing it with the input signal to generate error signals, and feeding these errors back to the input to cancel distortion. This feedback mechanism enables high-efficiency non-linear amplifiers to achieve linear operation by continuously correcting distortion products.
Solution Approach 2:
The patent introduces baseband error signals as intermediaries between the non-linear amplifier output and the input signal. These error signals, generated through down-conversion and subtraction operations, serve as mediators that carry distortion information back to the input stage where they cancel the original distortion, enabling the amplifier to operate efficiently while maintaining linearity.
2Object-generated harmful factors
If classical correction techniques (feed-forward, pre-distortion, adaptive bias, synthesis) are used to correct distortion, then distortion correction is achieved, but device complexity and power consumption increase
Solution Approach 1:
The Cartesian feedback approach simplifies the correction architecture by using direct feedback of baseband error signals rather than complex feed-forward paths or pre-distortion networks. The feedback loop naturally adapts to amplifier characteristics, reducing the need for complex calibration circuits and multiple correction stages.
Solution Approach 2:
The system performs self-correction by automatically generating error signals from its own output and using these signals to cancel distortion at the input. The feedback mechanism continuously adapts to changes in amplifier operation, eliminating the need for external calibration or complex control systems.
3Object-generated harmful factors
If classical correction techniques are implemented to correct distortion in high-efficiency amplifiers, then distortion correction effectiveness is limited, but this restricts bandwidth and increases power consumption
Solution Approach 1:
The Cartesian feedback system operates across the entire amplifier bandwidth by continuously monitoring the output and feeding back error signals. Unlike narrowband pre-distortion techniques, the feedback approach adapts to frequency variations automatically, maintaining effective distortion correction across wide bandwidths without requiring multiple correction networks.
Solution Approach 2:
The feedback mechanism serves multiple functions simultaneously: it corrects amplitude distortion, phase distortion, and frequency-dependent effects across the entire operating bandwidth. The single feedback loop handles all correction tasks that would otherwise require multiple specialized circuits, simplifying the overall design while improving bandwidth performance.
Data Source
AI summary
A method of reducing distortion in the output of an amplifier is provided. The method comprises subtractively combining baseband error signals with the appropriate phase shift with baseband input signals, the baseband error signals generated by subtractively combining delayed fed-forward portions of the baseband input signals with baseband converted portions of a fed-back amplified output signal, the amplified output signal being a distorted replica of combined up-converted baseband input signals. The baseband error signals being filtered prior to the combining function, and also providing inputs to a controller which adjusts active elements of the amplification and fed-back paths in order to minimize the distortion within the output of the amplifier.