Neural-Network DPD Modeling for PA Gain Oscillation Control
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Solution Overview
Problem
High-power RF power amplifiers (PAs) face challenges in achieving linearity due to drain inductor resonance, leading to gain oscillations and unwanted out-of-band emissions, which are difficult to mitigate with conventional digital predistortion (DPD) methods, especially at high sampling rates and in 5G wireless communications.
Innovation Solution
A neural-network-assisted physical model is used to precompensate for PA gain oscillations by processing the input signal with an envelope regulator circuit and updating DPD coefficients based on feedback, employing a parameterized model that includes a finite impulse response (FIR) filter and a two-dimensional lookup table to map voltage variations and signal envelopes to gain values, thereby mitigating the effects of drain inductor resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional digital predistortion methods are used, then the system is simple to implement, but drain inductor resonance causing gain oscillations and out-of-band emissions cannot be effectively mitigated
Solution Approach 1:
A neural network is introduced as an intermediary component between the input signal and the DPD processing chain. The neural network takes the input signal envelope and PA drain voltage as inputs, processes them through learned parameters, and outputs a correction signal that compensates for drain inductor resonance effects. This intermediary neural network model enables effective mitigation of gain oscillations and out-of-band emissions while maintaining a structured and interpretable system architecture.
2Measurement precision
If high sampling rates are used, then DPD accuracy is improved, but computational complexity and processing requirements increase
Solution Approach 1:
The system changes the parameter of sampling rate to match the PA bandwidth rather than using excessively high rates. The neural network processes signals at this optimized sampling rate, and the model parameters (weights and biases) are trained to achieve high DPD accuracy at this reduced rate. This parameter optimization reduces computational complexity and processing requirements while maintaining the necessary DPD accuracy for effective resonance mitigation.
Data Source
AI summary
Systems, devices, and methods related to envelope regulated, digital predistortion (DPD) are provided. An example apparatus includes an envelope regulator circuit to process, based on a parameterized model, an input signal to generate an envelope regulated signal; a digital predistortion (DPD) actuator circuit to process the envelope regulated signal and the input signal based on DPD coefficients associated with a nonlinearity characteristic of a nonlinear component; and a DPD adaptation circuit to update the DPD coefficients based on a feedback signal indicative of an output of the nonlinear component.


