RF Predistortion Control for Power Amplifier Harmonic Cancellation
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Solution Overview
Problem
Wideband power amplifiers suffer from performance deterioration due to in-band harmonics, out-band higher-order harmonics, and spectral regrowth, which existing digital-predistortion techniques fail to adequately address, particularly in emerging 5G-NR and mm-Wave communication systems.
Innovation Solution
An extremum seeking controller is used to determine the phase and amplitude of an injected pre-distortion signal in the RF domain to cancel intermodulation and second harmonic components, optimizing the PA performance without complex modeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If digital-predistortion techniques are used to improve non-linearities, then in-band intermodulation components are reduced, but out-band harmonics and spectral regrowth remain unaddressed
Solution Approach 1:
The patent segments the distortion cancellation problem into two independent parts: baseband injection for in-band intermodulation cancellation and RF injection for out-band harmonic cancellation. This allows each injection path to be optimized independently for its specific frequency range and distortion type.
Solution Approach 2:
The patent introduces RF injection as an intermediary mechanism to bridge the gap between baseband predistortion and the actual cancellation of out-band harmonics. The RF injection path acts as a mediator that directly targets harmonic frequencies in the RF domain, complementing the baseband approach.
2Measurement precision
If extensive PA modeling is performed to improve predistortion accuracy, then in-band non-linearity correction is enhanced, but computational complexity increases
Solution Approach 1:
The patent extracts the essential cancellation parameters (amplitude and phase) directly from measured PA output characteristics without requiring comprehensive PA modeling. This extraction approach focuses only on the necessary parameters for distortion cancellation, avoiding the computational burden of extensive modeling.
Solution Approach 2:
The system performs self-adjustment by measuring its own output distortion and automatically tuning the injection signals to cancel the measured harmonics. This self-service mechanism eliminates the need for complex external modeling and characterization procedures.
3Reliability
If linear search is used to determine injection signal parameters, then convergence is guaranteed, but convergence time is excessive
Solution Approach 1:
The patent implements a feedback mechanism where the PA output is continuously monitored and the injection signal parameters are adjusted based on measured distortion levels. This closed-loop feedback enables rapid convergence to optimal cancellation parameters without exhaustive linear search.
Solution Approach 2:
The system dynamically adapts the injection signal parameters in real-time based on operating conditions. Rather than using static pre-computed values from extensive modeling, the parameters are continuously optimized through feedback, enabling fast convergence to the current optimal state.
Data Source
AI summary
A signal transmitter for transmitting signals in a radio frequency (RF) domain is provided. The transmitter comprises circuitry configured to receive a source RF signal in the RF domain and produce a pre-distortion RF signal in the RF domain with a phase and a magnitude dependent on a phase and a magnitude of the source RF signal. The circuitry is further configured to combine the source RF signal and the pre-distortion RF signal to produce a combined RF signal and amplify the combined RF signal to produce an amplified RF signal. The circuitry outputs the amplified RF signal through a suitable transmission medium. An extremum seeking controller determines the phase and amplitude of the pre-distortion RF signal based on the phase and amplitude of the source RF signal.