Digital Pre-Distortion Circuit for Out-of-Band ACLR Correction
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Solution Overview
Problem
Digital pre-distortion techniques are limited in correcting distortions outside the bandwidth of the digital-to-analog converter, leading to incomplete correction of adjacent channel leakage ratio and other distortion phenomena in communication systems.
Innovation Solution
A digital pre-distortion circuit and method that filters out signals outside the limited bandwidth of the digital-to-analog converter and estimates an output signal with a larger bandwidth, allowing for pre-distortion training and parameter determination to correct distortions beyond the converter's bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the bandwidth of DAC and ADC is limited, then the device complexity and cost are reduced, but the ability to correct distortions outside the bandwidth is lost
Solution Approach 1:
The patent divides the signal processing into two paths: one for in-band signals (within DAC bandwidth) and one for out-of-band signals (above DAC bandwidth). The feedback path processes signals within the limited bandwidth, while the feedforward path processes signals beyond the bandwidth. This segmentation allows the system to correct both in-band and out-of-band distortions simultaneously, resolving the contradiction between limited bandwidth hardware and comprehensive distortion correction capability.
2Reliability
If the bandwidth of DAC and ADC is increased to 5 times the signal bandwidth, then the adjacent channel leakage ratio can be fully corrected, but the device complexity and cost increase significantly
Solution Approach 1:
The patent segments the distortion correction function into two independent paths: feedback path for in-band correction and feedforward path for out-of-band correction. This allows using limited-bandwidth DAC and ADC (avoiding 5x bandwidth requirement) while still achieving comprehensive distortion correction through the combined action of both paths.
Solution Approach 2:
The patent introduces an intermediary signal processing approach where the feedforward path acts as a mediator to handle out-of-band signals that the limited-bandwidth feedback path cannot process. The feedforward path processes the original input signal directly to compensate for out-of-band distortions, bridging the gap created by the bandwidth limitation of the DAC and ADC.
3Device complexity
If conventional DPD technique is used with limited bandwidth DAC and ADC, then the device complexity is reduced, but the correction of distortions outside bandwidth is incomplete
Solution Approach 1:
The patent segments the distortion correction into feedback path (in-band) and feedforward path (out-of-band), allowing complete distortion correction with limited bandwidth hardware.
Solution Approach 2:
The feedforward path performs preliminary distortion compensation on the input signal before amplification. By calculating and applying pre-distortion coefficients based on the power amplifier's characteristics, the system proactively corrects out-of-band distortions before they occur, improving signal quality without requiring higher bandwidth hardware.
Data Source
AI summary
A digital pre-distortion circuit and a digital pre-distortion method are provided. In the method, pre-distortion, digital-to-analog conversion and an amplifying process are performed on an input signal in sequence, to generate an output signal. A first bandwidth of the input signal after the pre-distortion is greater than a second bandwidth of the input signal after the digital-to-analog conversion. Signals outside the second bandwidth are filtered out from the output signal, to generate a second output signal. A third output signal, which is a signal after a pre-distorted signal is amplified, is estimated according to the pre-distorted signal and the second output signal. The pre-distorted signal is a signal after the pre-distortion is performed on the input signal. A third bandwidth of the third output signal is greater than the second bandwidth. Parameters of the pre-distortion can be determined according to the third output signal and the pre-distorted signal.