Digital Pre-Distortion System with Low Sampling Rate Observation Loop
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Solution Overview
Problem
Current Digital Pre-Distortion (DPD) systems in RF transmitters face challenges due to the high sampling rate requirements of Analog-to-Digital Converters (ADCs) in the observation loop, which exceed the limits of current technology and increase costs, especially when capturing bandwidths up to 1 GHz.
Innovation Solution
A DPD architecture that allows for a sampling rate in the observation loop to be arbitrarily low, determined by adaptation convergence time requirements, using a pre-distortion module, adaptation module, and a linear adaptive FIR filter to compensate for distortion and reduce power consumption and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the ADC sampling rate is increased to meet Nyquist requirements for 1 GHz bandwidth, then the distortion cancellation precision is improved, but the power consumption and cost increase
Solution Approach 1:
The patent segments the signal processing into two distinct paths: a high-speed path for distortion cancellation that operates at the full signal bandwidth, and a low-speed path for adaptation that operates at a reduced sampling rate. This segmentation allows the ADC to run at low power while maintaining high distortion cancellation precision through the separate high-speed processing path.
Solution Approach 2:
The patent implements dynamic operation by allowing the adaptation loop to run at variable sampling rates depending on convergence requirements, while the distortion cancellation path maintains high-speed operation. This dynamic approach enables the system to optimize power consumption based on real-time performance needs without sacrificing distortion cancellation precision.
2Measurement precision
If the ADC sampling rate is increased to meet Nyquist requirements for 1 GHz bandwidth, then the distortion cancellation precision is improved, but the system cost increases
Solution Approach 1:
The patent segments the ADC functionality into two operational modes: a low-power observation mode for adaptation that runs at reduced sampling rates, and a high-performance mode for distortion cancellation that operates at full bandwidth. This segmentation eliminates the need for a single high-cost, high-speed ADC, replacing it with a lower-cost ADC that achieves the same overall performance through divided functionality.
Solution Approach 2:
The patent introduces an intermediary processing path that takes the low-speed ADC output and generates adaptation coefficients, which are then applied in the high-speed distortion cancellation path. This intermediary adaptation loop acts as a mediator that bridges the gap between low-speed observation and high-speed cancellation, allowing the use of lower-cost ADC hardware.
3Use of energy by moving object
If the sampling rate is reduced below Nyquist rate, then the power consumption is reduced, but the adaptation convergence time increases
Solution Approach 1:
The patent implements dynamic adaptation where the low-speed sampling path continuously updates the distortion cancellation coefficients as convergence is achieved. The system adapts in real-time at the reduced sampling rate, allowing power reduction without permanently increasing convergence time, as the adaptation continues progressively.
Solution Approach 2:
The patent maintains continuous useful action by keeping the adaptation loop actively running at the reduced sampling rate, continuously refining the distortion cancellation coefficients. This continuous adaptation ensures that even at lower sampling rates, the system progressively converges without significant time loss, as the useful adaptation action never stops.
Data Source
AI summary
A system includes a digital to analog converter, a power amplifier, an analog-to-digital converter, a filter, and a pre-distortion module. The digital to analog converter generates analog data based on digital data. The power amplifier generates output data based on the analog data. The analog-to-digital converter generates samples based on the output data at a sampling rate less than a Nyquist sampling rate. The filter filters the digital data and generates filtered data. The pre-distortion module distorts the digital data based on the samples and the filtered data to compensate for distortion generated by the power amplifier.