Envelope Tracking Supply Modulation With Bandwidth-Compressed Control
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Solution Overview
Problem
The use of full-bandwidth envelope signals for envelope tracking in power amplifier circuits results in inefficiencies due to stringent specifications on linearity, bandwidth, and efficiency, leading to unacceptably low efficiency and potential distortion in amplified signals, especially in digital modulation schemes where coherent demodulation is performed.
Innovation Solution
A bandwidth-compressed envelope tracking signal is generated by filtering the full-bandwidth envelope signal to a narrower bandwidth, which is then used to modulate the supply node of the power amplifier, enhancing efficiency while maintaining acceptable linearity, using a tapped delay line and bandwidth-compressing circuit to identify peak magnitudes and align the signal temporally with the compressed envelope tracking signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a full-bandwidth envelope signal is used for envelope tracking, then the power amplifier can operate with high efficiency, but the system requires stringent specifications on linearity, bandwidth, and efficiency leading to unacceptably low overall efficiency
Solution Approach 1:
The patent extracts only the essential envelope information from the full-bandwidth signal by detecting peak magnitudes and generating a simplified envelope tracking signal. This extracted envelope signal contains sufficient information to modulate the power amplifier supply while avoiding the complexity and inefficiency of processing the complete full-bandwidth signal through the envelope tracking chain.
2Use of energy by moving object
If the power amplifier is operated closer to amplitude compression to improve efficiency, then drain efficiency increases, but distortion and noise in the amplified signal increase due to non-linear behavior
Solution Approach 1:
The patent applies preliminary action by pre-modulating the power amplifier supply voltage with the envelope tracking signal before the power amplifier processes the main signal. This preliminary supply modulation prepares the amplifier to operate efficiently across the full dynamic range of the signal, allowing the amplifier to maintain linearity even when operating closer to compression points, thereby reducing distortion while improving efficiency.
Data Source
Figure 1A~1B
Figure 1C
Figure 2A
AI summary
An envelope tracking scheme can be used, such as to modulate a supply node of a power amplifier circuit to improve efficiency. For example, a magnitude or amplitude envelope of a signal to be modulated can be scaled and used to drive a node, such as a drain, of the power amplifier circuit. An envelope tracking signal can be generated such as having a bandwidth that is compressed as compared to a full-bandwidth envelope signal. A peak-value "look ahead" technique can be used, for example, so that amplitude compression or clipping of the transmit signal is suppressed when the bandwidth-compressed envelope tracking signal is used to modulate a supply node of the power amplifier used to amplify the transmit signal.