Single Feedback Mixer DPD for Power Amplifier Linearity
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Solution Overview
Problem
Power amplifier circuits in wireless systems suffer from distortion due to large swings in output power levels, limiting their performance and requiring either discrete IC fabrication with high manufacturing costs or restricted output power levels, which reduce transmission range and quality.
Innovation Solution
A digital predistortion scheme using a single feedback mixer estimates and compensates for amplitude modulation to amplitude modulation (AM-AM) and amplitude modulation to phase modulation (AM-PM) distortion by adjusting input power levels and phases, allowing for linear output power amplification across a wider range without increasing pin count or output power restrictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power amplifier circuits operate with large swings in output power levels, then transmission range and quality are improved, but distortion increases limiting performance
Solution Approach 1:
The system performs preliminary characterization of the power amplifier's distortion behavior by measuring AM-AM and AM-PM distortion across multiple input power levels. This pre-acquired distortion data is stored and later used to generate correction factors that predistort the input signal, compensating for expected distortion before the signal reaches the power amplifier.
Solution Approach 2:
The system establishes a feedback loop where the power amplifier's output is monitored and the measured distortion characteristics are used to adjust the input signal. The baseband processor continuously characterizes the PA's distortion behavior and updates correction factors accordingly, creating a closed-loop system that adapts to changing operating conditions and maintains optimal performance.
2Manufacturing precision
If discrete IC fabrication is used to reduce distortion, then distortion performance is improved, but manufacturing cost increases
Solution Approach 1:
The system replaces physical hardware modifications (such as discrete IC fabrication or additional analog distortion compensation circuits) with digital signal processing techniques. The baseband processor uses software-based algorithms to characterize and correct distortion, substituting complex analog hardware solutions with flexible digital processing that achieves the same distortion compensation goal at lower manufacturing cost.
Solution Approach 2:
The system changes the operating parameters of the power amplifier through digital predistortion rather than modifying the physical amplifier hardware. By adjusting the input signal's amplitude and phase parameters in the digital domain before amplification, the system compensates for nonlinearities without requiring changes to the amplifier's physical construction or materials.
3Manufacturing precision
If output power levels are restricted to reduce distortion, then distortion performance is improved, but transmission range decreases
Solution Approach 1:
The system applies preliminary anti-action by predistorting the input signal in the opposite direction of the expected distortion. The baseband processor calculates correction factors that pre-compensate for the power amplifier's nonlinear behavior, effectively canceling out the distortion before it occurs. This allows the amplifier to operate at high output power levels without suffering from the usual distortion penalties.
4Device complexity
If integration of RF transmitter circuitry is increased, then device complexity is reduced, but distortion performance deteriorates
Solution Approach 1:
The system substitutes complex analog distortion compensation hardware with digital signal processing implemented in the baseband processor. This digital approach maintains compatibility with integrated RF transmitter circuitry while achieving effective distortion compensation, allowing high integration levels without sacrificing distortion performance.
Data Source
AI summary
Aspects of a method and system for compensating for estimated distortion in a transmitter by utilizing a digital predistortion scheme with a single feedback mixer are presented. Aspects of the system may include at least one circuit that enables generation of an output signal in response to one or more generated input signals. A feedback signal may be generated within a single feedback mixer circuit that may perform a frequency mix-down operation on the generated output signal. The generated feedback signal may be inserted at one or more insertion points in a receiver. Each of the insertion points may be located between a mixer stage of the receiver, and one or more circuits that generate a baseband signal based on the generated feedback signal.