Adaptive Digital Predistortion for Power Amplifier Linearization
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Solution Overview
Problem
Existing power amplifiers in communication systems, particularly in cellular networks, suffer from non-linear output characteristics due to transistor saturation, leading to distortion and inefficiency, which is exacerbated by the need to operate within linear regions to maintain performance standards, resulting in increased power consumption and costs.
Innovation Solution
A system and method employing digital predistortion circuitry with memoryless and short-duration memory predistortion functions, combined with a QR decomposition function to synthesize compensating error signals, effectively linearizing the power amplifier by addressing both short-term and long-term memory effects, allowing for real-time adaptation and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power amplifiers operate in the saturation region to increase transmit power, then power output increases, but non-linear distortion increases
Solution Approach 1:
The system applies digital predistortion to the input signal before amplification, pre-compensating for the expected non-linear distortion. This preliminary action ensures that when the signal passes through the saturation region of the power amplifier, the pre-applied distortion correction counteracts the amplifier's non-linear behavior, maintaining signal fidelity while enabling high power operation
Solution Approach 2:
The system incorporates a feedback path that monitors the actual output signal from the power amplifier and uses this information to adjust the predistortion parameters. This closed-loop feedback mechanism continuously adapts the predistortion correction to match the actual non-linear characteristics of the amplifier, ensuring optimal distortion compensation across varying operating conditions
2Object-generated harmful factors
If power amplifiers operate in the linear region to reduce distortion, then signal fidelity improves, but power efficiency deteriorates
Solution Approach 1:
By applying predistortion correction before amplification, the system enables the power amplifier to operate in the saturation region (high efficiency) while maintaining linear output characteristics. The preliminary distortion compensation allows the amplifier to push harder without sacrificing signal fidelity, thus improving power efficiency while controlling distortion
Solution Approach 2:
The system dynamically adjusts the predistortion parameters based on the operating conditions and actual amplifier characteristics. By changing the predistortion parameters in real-time, the system optimizes the balance between power efficiency and distortion reduction, allowing the amplifier to operate at maximum efficiency while maintaining signal quality
3Object-generated harmful factors
If digital predistortion is applied to linearize power amplifier output, then distortion is reduced, but device complexity increases
Solution Approach 1:
The system replaces complex analog predistortion circuitry with digital signal processing implementations. By using digital algorithms to perform the predistortion function, the system achieves accurate distortion compensation while reducing hardware complexity, improving manufacturability, and enabling easier parameter adjustment through software rather than complex analog component design
Data Source
AI summary
System and methods for a digital linearization of a non-linear element. Preferred embodiments provide digital predistortion methods and circuitry that addresses long or “memory” effects and separately shorter duration effects, these two predistortion functions are operated together in an adaptive fashion with a non-linear element to provide a highly linear system. A long predistortion block comprises a plurality of configurable parallel coupled memory blocks, each further comprising a programmable nonlinearity, variable delays, digital filters, and signal combiners. These parallel blocks are selectively configured to provide a parallel filter, a Hammerstein filter and a compound Volterra filter. The parallel coupled memory blocks include programmable parameters that enable real time adaptation of the predistortion; the delay elements also include variable delays. The combined system of the predistortion circuitry and a non-linear element has a linear input-output signal response. Methods for initializing, parameterizing and adapting the system are disclosed.