Supply-Modulated RF Amplifier Envelope Bandwidth Reduction
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Solution Overview
Problem
Designing power amplifiers for wideband wireless communication systems is challenging due to high peak-to-average power ratios, with traditional Class AB amplifiers being inefficient, and newer supply-modulated amplifiers facing bottlenecks in power supply modulator design as bandwidth increases.
Innovation Solution
Generating a reduced bandwidth envelope signal for the power supply modulator of RF amplifiers through iterative low-pass filtering and rectification processes, allowing for a slowly varying power supply waveform that maintains high efficiency while compensating for introduced distortion with adaptive pre-distortion of the RF input signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If supply-modulated amplifiers (ET, EER) are used to improve power efficiency in wideband systems, then power efficiency is improved, but the design complexity of the power supply modulator increases and becomes the design bottleneck
Solution Approach 1:
The patent segments the envelope signal processing into two distinct parts: the main envelope signal path and the residue signal path. The residue signal represents the difference between the original envelope and the bandwidth-reduced envelope, and processing this residue separately allows the system to achieve accurate envelope tracking while using a simpler, lower-bandwidth power supply modulator. This segmentation resolves the contradiction by maintaining power efficiency through accurate envelope following while reducing modulator design complexity.
Solution Approach 2:
The patent introduces an intermediary residue signal as a mediator between the original high-bandwidth envelope signal and the bandwidth-reduced power supply envelope signal. This residue signal captures the high-frequency components that are filtered out, and by processing it through a separate path (including rectification and addition), the system ensures that the power supply modulator only needs to handle the reduced bandwidth component, thereby simplifying its design while maintaining overall signal fidelity.
2Device complexity
If bandwidth reduction is applied to the envelope signal to simplify power supply modulator design, then modulator design is simplified, but signal accuracy and linearity deteriorate
Solution Approach 1:
The patent employs feedback by continuously monitoring the residue signal (the difference between original and bandwidth-reduced envelope signals) and feeding it back through a processing path that includes rectification, filtering, and addition. This feedback mechanism ensures that the components removed by bandwidth reduction are reconstructed and added back to the power supply envelope signal, thereby maintaining signal accuracy and linearity despite the initial bandwidth reduction that simplified the modulator design.
Solution Approach 2:
The patent converts the harmful effect of bandwidth reduction (signal accuracy loss) into a benefit by treating the removed high-frequency components as a separate residue signal. This residue is then processed through rectification and addition to reconstruct the complete envelope information. The harm of bandwidth reduction is thus transformed into a manageable intermediate representation that can be accurately reconstructed, resolving the contradiction between simplified modulator design and maintained signal accuracy.
3Manufacturing precision
If iterative residue processing is performed to maintain signal accuracy, then signal accuracy is improved, but processing time and computational complexity increase
Solution Approach 1:
The patent applies partial action by performing residue processing to the extent necessary to restore signal accuracy without excessive iteration. The residue signal is processed through rectification, filtering, and addition in a single pass through the feedback path, which is sufficient to reconstruct the envelope information accurately. This avoids the need for multiple iterative cycles, thereby maintaining signal accuracy while minimizing processing time and computational complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the design of power supply modulators, improves efficiency and linearity for wideband applications, and provides flexible trade-offs between supply modulator and RF power amplifier performance, despite introducing some distortion which is effectively managed by pre-distortion.
Implementation Method 1
An envelope signal of an RF amplifier input Venv(t) is low pass filtered
Implementation Method 2
The filtered envelope signal is subtracted from the envelope signal to obtain a difference signal, which is rectified to produce a residue signal
Implementation Method 3
envelope tracking (ET) or envelope elimination and restoration (EER) power amplifiers
Implementation Method 4
supply-modulated RF power amplifiers such as the ET, EER, wideband ET amplifiers
Data Source
AI summary
An embodiment of the invention is a method of generating a reduced bandwidth envelope signal VDD(t) for the power supply modulator of an RF amplifier. An envelope signal of an RF amplifier input Venv(t) is low pass filtered. The filtered envelope signal is subtracted from the envelope signal to obtain a difference signal, which is rectified to produce a residue signal. The residue signal is low pass filtered and added back into the filtered envelope signal. An iterative process of the rectifying, low pass filtering the residue signal adding it back is continued until a condition of VDD(t)≧Venv(t) is met. Another embodiment provides a method of generating a reduced bandwidth envelope signal VDD(t) for the power supply modulator of an RF amplifier. An envelope signal of an RF amplifier input Venv(t) is low pass filtered. The filtered envelope signal is subtracted from the envelope signal to obtain a difference signal, which is rectified to produce a residue signal. The residue signal is low pass filtered and multiplied by a first constant that is greater than one, and then added back into the filtered envelope signal. A second constant is added into the filtered envelope signal so that the condition VDD(t)≧Venv(t) is met.