Envelope Tracking Linear Amplifier Offset Current for Lower Dissipation
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Solution Overview
Problem
Existing envelope tracking power supplies for RF power amplifiers face inefficiencies due to significant power dissipation in the output stage of linear amplifiers, particularly because of asymmetry in the modulator output voltage, leading to unequal average currents in current sources and sinks, which results in higher power dissipation in one device over the other.
Innovation Solution
The introduction of a DC offset current at the high frequency output stage using a separate voltage supply, connected via an inductor, allows for unequal average source and sink currents, reducing power dissipation by modifying the current flow through the addition of an offset current, which is either directly sensed or calculated based on the input waveform asymmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linear amplifier is used in the high frequency path for envelope tracking, then tracking accuracy is improved, but power dissipation in the output stage increases significantly
Solution Approach 1:
The patent changes the operating parameters of the linear amplifier by introducing a DC offset current that shifts the average voltage level. This parameter change allows the amplifier to operate in a more efficient region while maintaining tracking accuracy, directly reducing power dissipation in the output stage.
Solution Approach 2:
The patent deliberately introduces asymmetry by adding a DC offset current that creates unequal average currents in the current source and sink. This asymmetric operation compensates for the inherent asymmetry in envelope tracking waveforms, reducing the power dissipation imbalance and overall power loss in the output stage.
2Loss of energy
If asymmetry in modulator output voltage is reduced, then power dissipation decreases, but additional circuit complexity is introduced
Solution Approach 1:
The patent introduces a DC offset current as an intermediary element that mediates between the asymmetric envelope tracking requirements and the symmetric power dissipation constraints. This intermediary current balances the power dissipation in the output stage without requiring fundamental changes to the amplifier architecture.
Solution Approach 2:
The DC offset current serves multiple functions simultaneously: it reduces power dissipation, maintains tracking accuracy, and compensates for waveform asymmetry. This multi-functionality achieves power reduction without proportionally increasing circuit 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 reduces power dissipation by approximately 20% in the output stage, improving efficiency by allowing the power supply to operate with reduced asymmetry and minimizing total sensed power, thus enhancing the overall performance of the envelope tracking power supply.
Implementation Method 1
The DC offset current may be provided via an inductor connected between the further power supply and the high frequency output
Data Source
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AI summary
There is disclosed an envelope tracking power supply arranged to generate a modulated supply voltage in dependence on a reference signal, comprising a first path for tracking low frequency variations in the reference signal and a second path for tracking high frequency variations in the reference signal, the second path including a linear amplifier, wherein the output of the linear amplifier comprises a current source and a current sink connected to the high frequency output, there further being provided a DC offset current at the high frequency output.