Digital Pre-Distortion Observation Path Using RF Undersampling
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Solution Overview
Problem
Power amplifiers in base transceiver stations face challenges in achieving high efficiency and linearity over a large amplitude range, leading to non-linearity issues that are difficult to correct due to memory effects, particularly in mobile communication standards, which affects adjacent channel leakage ratio and error vector magnitude.
Innovation Solution
A digital pre-distortion system that uses an undersampling analog-to-digital converter to sample the output signal of the power amplifier at a rate below the Nyquist rate, eliminating the need for down mixing and anti-aliasing modules, and employs adaptive algorithms to correct non-linearity, allowing for more freedom in choosing sampling rates and reducing system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Nyquist-rate sampling is used to accurately capture the power amplifier output signal, then measurement precision is improved, but device complexity and cost increase due to requiring high-speed ADCs and associated down mixing/anti-aliasing modules
Solution Approach 1:
The patent replaces the conventional mechanical/analog signal processing chain (down mixers, anti-aliasing filters, high-speed ADCs) with a digital subsampling approach. By using an ADC running at a fraction of the Nyquist rate (e.g., 1/4 or 1/8 the original sampling rate), the system captures only the necessary signal information for DPD correction, eliminating complex analog circuitry while maintaining measurement accuracy for the power amplifier's non-linear distortion products
Solution Approach 2:
The invention extracts only the essential signal components needed for power amplifier non-linearity correction by using subsampling. Instead of capturing the entire broadband signal at full Nyquist rate, the system extracts the relevant baseband or low-frequency components that contain the distortion information, discarding unnecessary high-frequency content that would require complex processing
2Measurement precision
If high-speed ADCs with Nyquist-rate sampling are used, then signal observation accuracy is improved, but loss of energy increases due to higher power consumption of fast ADCs
Solution Approach 1:
The patent fundamentally changes the sampling rate parameter from full Nyquist rate to a subsampled rate (e.g., 1/4 or 1/8 of Nyquist). This parameter change enables the use of lower-speed, lower-power ADCs while still capturing sufficient signal information for effective power amplifier non-linearity correction, directly reducing the energy consumption of the observation path
3Measurement precision
If downsampling and anti-aliasing modules are included in the observation path, then signal measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent replaces the analog down mixing and anti-aliasing filter modules with a digital subsampling ADC approach. The ADC is configured to directly subsample the RF or intermediate frequency signal, and digital signal processing algorithms compensate for any aliasing effects, eliminating the need for complex analog filtering and frequency conversion hardware in the observation path
Data Source
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AI summary
Various digital pre-distortion systems for use in transmitters are disclosed. The digital pre-distortion system comprises an observing path, which performs either undersampling or radio frequency sampling of the output of a power amplifier. Undersampling may be performed at a rate, which causes aliasing to occur in the undersampled frequency domain. Both undersampling and radio frequency sampling reduces the complexity of the digital pre-distortion system by removing any down mixing modules or anti-aliasing modules, while maintaining reasonable performance of the digital pre-distortion systems.