Replica Linearized Power Amplifier for GSM and EDGE Stability
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Solution Overview
Problem
Existing power amplifiers in portable communication devices, particularly those using linear power amplifiers for non-constant envelope modulation, face inefficiencies and saturation issues when switching between GSM and EDGE modes, leading to increased power consumption and potential instability due to amplitude modulation distorting phase modulation signals.
Innovation Solution
A replica linearized power amplifier is introduced, featuring a power amplifier core with an additional amplification device that generates a control signal proportional to its output, utilizing closed-loop feedback to maintain linear control and minimize distortion through inner and outer AM correction loops and a phase correction loop, ensuring stable operation across varying loads and conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a linear power amplifier is used for non-constant envelope modulation (EDGE), then the amplifier can handle amplitude and phase modulated waveforms, but the power consumption increases significantly compared to nonlinear amplifiers
Solution Approach 1:
The power amplifier is segmented into two functional parts: a nonlinear power amplifier core that provides high efficiency, and a separate linearization circuit that restores amplitude linearity. This segmentation allows the amplifier to operate efficiently in nonlinear mode while still supporting non-constant envelope modulation through the linearization stage.
Solution Approach 2:
A linearization circuit acts as an intermediary between the nonlinear power amplifier and the modulation signal. This intermediary component (using techniques like predistortion or feedback linearization) corrects the amplitude distortion introduced by the nonlinear amplifier, enabling EDGE compatibility without sacrificing the efficiency benefits of nonlinear operation.
2Power
If amplitude modulation is applied to control power amplifier output, then power control is achieved, but the AM signal distorts the PM signal due to nonlinearities
Solution Approach 1:
The linearization circuit applies preliminary anti-action by predistorting the input signal in the opposite direction of the expected nonlinear distortion. This pre-correction prevents the AM signal from distorting the PM signal when the control voltage varies, maintaining signal integrity throughout the power control range.
Solution Approach 2:
A feedback mechanism monitors the actual output signal and adjusts the input signal or amplifier parameters to compensate for nonlinearities. This closed-loop feedback ensures that phase modulation remains undistorted even as amplitude control varies the operating point of the power amplifier.
3Use of energy by moving object
If the power amplifier operates in GSM mode with constant envelope modulation, then efficiency is maintained, but the amplifier cannot properly handle EDGE mode with non-constant envelope modulation
Solution Approach 1:
The power amplifier incorporates dynamic adaptability through the linearization circuit that can adjust its characteristics based on the input signal type. The system dynamically switches or adjusts its operation mode - operating as a simple efficient nonlinear amplifier for GSM constant envelope signals, and activating the linearization function for EDGE non-constant envelope signals.
Solution Approach 2:
The power amplifier is designed with universal functionality to handle both constant envelope (GSM) and non-constant envelope (EDGE) modulation schemes. The same amplifier core serves both purposes, with the linearization circuit providing the additional capability needed for EDGE while maintaining efficiency for GSM operation.
4Manufacturing precision
If closed-loop feedback is used to correct amplitude and phase distortion, then linearity is improved, but the system becomes unstable and oscillates under output mismatch
Solution Approach 1:
The feedback system uses partial action by selectively correcting only the necessary distortion components rather than attempting full signal reconstruction. This selective feedback approach provides sufficient linearization for communication purposes while avoiding the excessive feedback gain that would cause instability under load mismatch conditions.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A power amplifier includes a power amplifier core in which a transmit signal having an amplitude-modulated (AM) component and a phase-modulated (PM) component is passed and amplified, the power amplifier comprising a forward path, and an additional amplification device configured to generate an output that is proportional to an output of the power amplifier core, such that the output of the additional amplification device indirectly controls the output of the power amplifier core.