GaN HEMT Power Amplifier Linearization for Memory Effect Drift
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Solution Overview
Problem
The existing power amplifiers for cellular base stations, particularly Doherty amplifiers using GaN HEMTs, suffer from gain variations due to the memory effect caused by momentary drain voltage changes, leading to poor distortion compensation by Digital Pre-distorters (DPDs).
Innovation Solution
A power amplifier configuration that includes a GaN HEMT amplifier, a diode linearizer, a variable attenuator, a peak detector, and a controller. The diode linearizer is activated when the peak drain voltage exceeds a threshold, and the variable attenuator reduces its attenuation amount accordingly, thereby reducing gain variations and improving linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a diode linearizer is activated to suppress amplitude and phase changes, then linearity is improved, but gain variation increases
Solution Approach 1:
A peak detector monitors the drain voltage of the amplifier and provides feedback to the controller. The controller adjusts the attenuation amount of the variable attenuator based on the detected peak voltage, creating a closed-loop feedback system that dynamically compensates for gain variations caused by the diode linearizer activation.
Solution Approach 2:
A variable attenuator is introduced as an intermediary component between the signal source and the amplifier input. This attenuator acts as a mediator that can dynamically adjust its attenuation amount to compensate for the gain changes introduced by the diode linearizer, thereby maintaining stable overall gain while preserving the linearity improvement.
2Manufacturing precision
If a DPD is used to compensate for distortion, then linearity is improved, but compensation fails when memory effect causes rapid AM-AM and AM-PM changes
Solution Approach 1:
The diode linearizer performs preliminary anti-action by gently changing the pass amplitude and phase in accordance with input power before the signal reaches the amplifier. This pre-distortion approach counteracts the memory effect and rapid characteristic changes, making the subsequent DPD compensation more reliable and effective across the entire operating range.
Solution Approach 2:
The system dynamically changes the attenuation parameter of the variable attenuator based on the peak drain voltage detected by the peak detector. This parameter adjustment allows the system to adapt to different operating conditions and maintain reliable distortion compensation even when memory effects cause rapid AM-AM and AM-PM changes.
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
The proposed solution effectively suppresses linearity deterioration and achieves the required distortion characteristics for base stations by compensating for the memory effect and reducing gain variations, even when DPDs struggle due to momentary drain voltage changes.
Implementation Method 1
A diode linearizer is suited to implement the above-described function in a power amplifier at a low price. Since a diode linearizer can gently change a pass amplitude and phase in accordance with input power by a diode linearizer, the diode linearizer can suppress amplitude and phase changes.
Implementation Method 2
a peak detector detecting a peak value of a drain voltage of the amplifier
Implementation Method 3
the variable attenuator reduces its attenuation amount accordingly, thereby reducing gain variations
Data Source
AI summary
An amplifier (Trc,Trp) uses a GaN HEMT. A diode linearizer (LNZ) and a variable attenuator (VATT) are connected in series to an input of the amplifier (Trc, Trp). A peak detector (DET) detects a peak value of a drain voltage of the amplifier (Trc,Trp). A controller (CTL) makes the diode linearizer (LNZ) function as a linearizer to reduce an attenuation amount of the variable attenuator (VATT) if the peak value exceeds a threshold.