Open-Loop Two-Stage Clipping for Low-Distortion Power Amplifiers
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Solution Overview
Problem
Power amplifiers face inefficiency and distortion issues when dealing with signals having high peak-to-average power ratios, leading to operation beyond saturation points and significant intermodulation distortion, especially in multicarrier signals.
Innovation Solution
A two-stage clipping method is employed to reduce the peak-to-average power ratio of input signals, introducing intermodulation distortion in the first stage that offsets distortion in the second stage, thereby minimizing overall intermodulation distortion without requiring knowledge of the amplifier's transfer function or output monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the power amplifier operates near saturation point to maximize efficiency, then energy conversion efficiency is improved, but signal distortion and intermodulation distortion increase dramatically
Solution Approach 1:
The patent applies preliminary action by pre-distorting the input signal before amplification. The pre-distortion circuit modifies the input signal in advance to compensate for the non-linear distortion that will occur during amplification, allowing the amplifier to operate near saturation while maintaining output signal quality.
Solution Approach 2:
The patent implements preliminary anti-action by introducing pre-distortion that is equal in magnitude but opposite in sign to the expected distortion from saturation operation. This pre-applied distortion counteracts the harmful distortion effects when the amplifier operates near its saturation point.
2Object-generated harmful factors
If the power amplifier operates with backoff to avoid saturation and distortion, then signal quality is improved, but energy conversion efficiency decreases
Solution Approach 1:
The pre-distortion circuit performs preliminary modification of the input signal to anticipate and compensate for saturation effects. This allows the system to operate at higher power levels without sacrificing signal quality, thereby improving efficiency compared to traditional backoff operation.
3Object-generated harmful factors
If pre-distortion is applied to offset intermodulation distortion, then distortion compensation is improved, but system complexity increases due to required amplifier characteristics knowledge or output monitoring
Solution Approach 1:
The patent employs a simplified pre-distortion approach that does not require expensive or complex feedback mechanisms. The pre-distortion parameters can be determined through relatively simple calibration procedures, avoiding the need for complex real-time monitoring systems or detailed amplifier modeling.
Solution Approach 2:
The system achieves distortion compensation through self-service by using the amplifier's own output characteristics to inform the pre-distortion parameters. The pre-distortion circuit is configured to compensate for the specific amplifier being used, creating a self-adapting system that does not require external monitoring or complex control mechanisms.
Data Source
AI summary
The peak-to-average power ratio of an input signal can be reduced prior to amplification. This reduction in the peak-to-average power ratio can be accomplished without adding significant intermodulation distortion to the input signal. The resulting input signal can therefore have a peak-to-average power ratio that does not exceed the output backoff of the amplifier thereby preventing the amplifier from being operated in saturation and, as a result, minimizing the intermodulation distortion added by the amplifier. The peak-to-average power ratio of an input signal can be reduced using two stages of signal clipping. By employing two stages, the intermodulation distortion introduced to the input signal as it passes through the stages is minimized. Also, because this two-stage approach does not attempt to account for intermodulation distortion introduced by the downstream amplifier, it can be implemented without any prior knowledge of the amplifier's transfer function or any output monitoring scheme.