Envelope Tracking Modulator Linear Amplifier With DC Offset Current
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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, primarily caused by asymmetry in the modulator output voltage and current, leading to unequal average source and sink currents.
Innovation Solution
The introduction of a DC offset current at the high frequency output stage, derived from a secondary voltage supply via an inductor, allows for unequal average source and sink currents, reducing power dissipation by modifying the current flow through the inclusion of a current source and sink connected to the high frequency output, and using a switch mode converter to generate this offset current based on sensed power differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linear amplifier is used in the high frequency path to track high frequency variations in the reference signal, then the power supply can provide accurate envelope tracking, but significant power dissipation occurs in the output stage due to asymmetry in the modulator output voltage and current
Solution Approach 1:
The patent applies asymmetry by introducing a DC offset current that creates unequal average source and sink currents in the output stage. This asymmetric current distribution compensates for the inherent asymmetry in the modulator output voltage waveform, allowing the linear amplifier to maintain high tracking accuracy while reducing power dissipation by approximately 20%.
2Ease of manufacture
If the average source and sink currents are kept equal in the output stage, then the circuit design is simplified, but power dissipation increases due to the asymmetry in the modulator output voltage
Solution Approach 1:
The patent changes the current parameter by introducing a DC offset current that creates unequal average source and sink currents. This parameter modification allows the circuit to operate more efficiently by matching the current distribution to the asymmetric voltage waveform, reducing power dissipation while maintaining design feasibility through a controlled current source implementation.
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 minimizes power dissipation in the output stage by approximately 20% and enhances the efficiency of the envelope tracking power supply, particularly for asymmetric waveforms, while maintaining the output current unchanged.
Implementation Method 1
there further being provided a DC offset current at the high frequency output
Implementation Method 2
using a switch mode converter to generate this offset current based on sensed power differences
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.