Power Amplifier Feedback Loops for Low-Delay AM-PM Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing power amplifiers in portable communication devices face inefficiencies when switching between constant and non-constant envelope modulation methodologies, leading to power consumption issues and potential saturation, especially when using nonlinear power amplifiers for both GSM and EDGE modes.
Innovation Solution
A low delay corrective feedback power amplifier control system with multiple control loops is implemented, including an outer AM correction loop, inner AM correction loop, and phase correction loop, to independently control amplitude and phase modulation, minimizing distortion and maintaining stability across varying load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linear power amplifier is used to implement EDGE mode with non-constant envelope modulation, then the amplifier can handle the modulation accurately, but the power consumption increases significantly and efficiency decreases
Solution Approach 1:
The patent segments the control of the nonlinear power amplifier into multiple independent control loops: an outer amplitude modulation (AM) loop that controls the envelope of the signal, and an inner phase modulation (PM) loop that controls the phase. This segmentation allows the nonlinear amplifier to be controlled in a way that achieves both constant envelope (for efficiency) and accurate modulation (for performance), resolving the contradiction between modulation accuracy and power efficiency.
2Use of energy by moving object
If a nonlinear power amplifier is used for GSM mode with constant envelope modulation, then power efficiency is improved, but the amplifier cannot accurately handle non-constant envelope modulation in EDGE mode
Solution Approach 1:
The patent implements a universal control architecture that can handle both constant envelope (GSM) and non-constant envelope (EDGE) modulation modes using the same nonlinear power amplifier. The outer AM loop and inner PM loop work together to achieve accurate signal reproduction regardless of the modulation type, allowing the amplifier to maintain high efficiency while being adaptable to different communication standards.
3Use of energy by moving object
If polar modulation is used with a nonlinear power amplifier, then power efficiency is maintained, but the system becomes unstable and oscillating under output mismatch conditions
Solution Approach 1:
The patent employs feedback mechanisms in both the outer AM loop and inner PM loop to maintain system stability. The loops continuously monitor the amplifier output and adjust the control signals accordingly, preventing oscillations and instability under varying load conditions while maintaining the efficiency benefits of using a nonlinear power amplifier with polar modulation.
4Measurement precision
If the power control loop bandwidth is increased to respond rapidly to modulation changes, then modulation accuracy improves, but the system becomes more prone to instability and oscillation
Solution Approach 1:
By segmenting the control into separate AM and PM loops with different bandwidths, the patent allows the inner PM loop to operate at a higher bandwidth for accurate phase tracking while the outer AM loop operates at a lower bandwidth for stable amplitude control. This segmentation enables the system to achieve high modulation accuracy without sacrificing stability.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A system for controlling the power output of a power amplifier includes a power amplifier through 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, a feedback signal comprising a portion of the output of the power amplifier, a first control loop configured to receive the feedback signal and configured to apply an amplitude modulated (AM) signal to the power amplifier and configured to control the gain of the power amplifier, a second control loop configured to receive the feedback signal and configured to correct for offsets in the forward path and to linearize the first control loop; and a third control loop configured to receive the feedback signal and configured to control the phase of the PM component of the transmit signal.