Envelope RF Amplifier Supply Filtering for Bandwidth and Linearity
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Solution Overview
Problem
Existing RF signal generation systems face inefficiencies and reduced output quality due to the wide bandwidth of envelope signals, which is exacerbated by non-linear operations and band-limiting techniques that introduce overshoots and undershoots.
Innovation Solution
Implementing a non-linear filtering method that restricts the bandwidth of the supply voltage based on an envelope-dependent boundary, ensuring the supply voltage stays closer to an optimum level and avoids regions of inefficiency, while modifying the input RF signal to compensate for non-linearities and maintain high efficiency and quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the envelope signal is band-limited by a linear low-pass filter to reduce bandwidth, then the efficiency of the envelope amplifier is improved, but the output signal quality deteriorates due to overshoots and undershoots
Solution Approach 1:
The patent changes the filtering approach from linear to non-linear, specifically using a non-linear low-pass filter that adapts its characteristics based on the envelope signal amplitude. This allows the filter to reduce bandwidth and improve efficiency while maintaining signal quality by preventing overshoots and undershoots that occur with fixed linear filtering.
Solution Approach 2:
The invention introduces dynamic behavior to the filtering process through an envelope-dependent boundary that adjusts in real-time based on the signal characteristics. This dynamic adaptation allows the system to optimize between bandwidth reduction and signal fidelity, unlike static linear filters.
2Loss of energy
If the envelope signal bandwidth is reduced to improve envelope amplifier efficiency, then energy loss is reduced, but the ability to represent the RF signal accurately deteriorates
Solution Approach 1:
The patent employs parameter changes by transitioning from linear filtering to non-linear filtering with an envelope-dependent boundary. This allows the system to reduce the envelope signal bandwidth for improved efficiency while the non-linear characteristics preserve the essential signal information that would otherwise be lost.
3Manufacturing precision
If a smooth curve is used to increase the envelope signal for low signal amplitudes to avoid inefficiency regions, then output quality is improved, but the efficiency is much reduced due to significant bandwidth reduction
Solution Approach 1:
The invention uses dynamic filtering with an envelope-dependent boundary that adapts to signal conditions. This allows the system to maintain high efficiency by reducing bandwidth only when appropriate, while still improving output quality through the non-linear filtering characteristics, avoiding the excessive bandwidth reduction required by static smooth curve methods.
Data Source
AI summary
RF signal generators (1) are disclosed, having an amplitude-modulated amplifier (80) whose supply voltage (70) is a signal non-linearly filtered (33) dependent on a signal (30) being representative to an envelope signal of a desired output RF signal (81). The non-linear filtering (33) is performed preferably using an envelope-dependent boundary. An input RF signal (65) to the amplifier (80) is amplified using the supply voltage (70) to produce the desired output RF signal (81). The present invention also presents methods for driving such generators (1).