Envelope Tracking Supply Predistortion for RF Voltage Alignment
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Solution Overview
Problem
Existing envelope tracking power supplies for RF amplifiers suffer from misalignment of supply voltage at the active device due to supply feed networks, leading to degraded RF output spectrum and transmission quality, especially as supply feed inductance increases.
Innovation Solution
Pre-distorting the supply voltage to compensate for effects such as supply feed inductance and shunt capacitance, ensuring the active device receives correctly aligned voltage at each instant, which is achieved by generating a target supply voltage, estimating current flowing in the active element, and applying inverse effects to the supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If envelope tracking power supply is used to improve efficiency, then power efficiency is improved, but supply voltage misalignment occurs at the active device
Solution Approach 1:
The patent applies pre-distortion to the supply voltage signal before it reaches the active device. This preliminary action compensates for the anticipated voltage drop across the feed network, ensuring that the correct voltage is delivered to the active device despite the presence of supply feed inductance and other parasitic elements.
Solution Approach 2:
The pre-distortion technique applies an opposing correction to the supply voltage signal that counteracts the harmful effects of the feed network. By introducing a compensating voltage that opposes the expected voltage drop, the system ensures accurate voltage delivery to the active device while maintaining envelope tracking efficiency.
2Power
If supply feed inductance is increased, then DC supply delivery is improved, but supply voltage alignment at active device deteriorates
Solution Approach 1:
The pre-distortion circuit calculates and applies a compensating voltage in advance that accounts for the voltage drop across the supply feed inductance. This allows the system to use sufficient inductance for proper DC supply delivery while maintaining accurate voltage alignment at the active device through the preliminary correction.
3Manufacturing precision
If pre-distortion is applied to compensate for supply feed effects, then supply voltage alignment is improved, but device complexity increases
Solution Approach 1:
The patent introduces a pre-distortion circuit as an intermediary component between the envelope tracker and the power amplifier. This intermediary applies the necessary compensation for feed network effects without requiring fundamental changes to the existing envelope tracking architecture, thereby improving voltage alignment while adding only moderate complexity.
4Loss of energy
If envelope tracking is implemented, then amplifier efficiency is improved, but RF output spectrum quality deteriorates
Solution Approach 1:
By applying pre-distortion to the supply voltage before it reaches the active device, the system maintains accurate voltage alignment throughout the envelope tracking operation. This preliminary correction prevents the supply voltage misalignment that would otherwise degrade RF output spectrum quality, thereby preserving both amplifier efficiency and spectral purity.
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 ensures constant RF gain irrespective of RF output power, improving the RF output spectrum and transmission quality by aligning the supply voltage with the intended operating point of the active device.
Implementation Method 1
the supply feed network causes errors in the supply voltage presented to the active device of the amplifier itself... These errors become more pronounced as the supply feed inductance increases
Implementation Method 2
The step of pre-distorting may compensate for the effects of at least one capacitor in the supply feed network of the amplifier
Data Source
AI summary
There is disclosed a method of generating a supply voltage (230) for a power amplifier (114) arranged to amplify an input signal (228), comprising: generating (104) a target supply voltage tracking the input signal (228); predistorting (400) the target supply voltage to compensate for effects on a supply voltage in the amplifier (114); and generating (102) the supply voltage for the amplifier (114) in dependence on the predistorted target supply voltage (414).