RF Power Amplifier Phase Loop Calibration for AM-to-PM Control
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Solution Overview
Problem
Conventional RF power amplifier systems face inefficiencies due to fixed biasing during off-peak amplitudes of RF signals, leading to wasted power and compromised spectral occupancy, especially with modulation techniques like WCDMA, and struggle with amplitude-to-phase modulation distortion and high electric quality band pass filters.
Innovation Solution
A power amplifier controller circuit with an amplitude control loop and phase control loop that adjusts the supply voltage and phase of the RF power amplifier using amplitude and phase correction signals, employing a switched mode power supply and variable gain amplifier to optimize efficiency and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed biasing is used during off-peak amplitudes of RF signals, then linearity requirements are met at peak power, but power is wasted and efficiency decreases
Solution Approach 1:
The patent implements dynamic biasing control by adjusting the bias voltage to the output transistor based on the instantaneous amplitude of the RF input signal. The bias control circuit continuously adapts the bias point, transitioning from fixed biasing to dynamic biasing that responds to signal conditions, thereby improving efficiency during off-peak periods while maintaining linearity when needed.
Solution Approach 2:
The patent employs feedback mechanisms where the amplitude of the RF input signal is detected and used to control the bias voltage. This closed-loop control ensures that the biasing conditions are continuously adjusted based on actual signal conditions, allowing the system to maintain linearity requirements while optimizing power efficiency through adaptive biasing.
2Use of energy by moving object
If supply voltage is varied to accommodate large variations in amplitude signal, then efficiency gains are achieved, but voltage converter complexity increases
Solution Approach 1:
The patent segments the control of supply voltage into two independent control voltages: a first control voltage for the amplitude signal path and a second control voltage for the supply voltage conversion. This segmentation allows the voltage converter to operate with simplified control logic while achieving efficiency gains through coordinated control of both the amplitude signal and supply voltage.
Solution Approach 2:
The patent introduces an intermediary amplitude-to-voltage converter that translates the amplitude signal into a control voltage for the supply voltage converter. This intermediary component simplifies the overall control architecture by decoupling the amplitude modulation path from the power supply control path, reducing the complexity of the voltage converter while maintaining energy efficiency.
3Reliability
If phase control loop is added to correct AM-to-PM distortion, then spectral efficiency improves, but device complexity increases
Solution Approach 1:
The patent merges the amplitude control loop and phase control loop into a single integrated controller circuit. By combining both control functions in one device, the patent achieves spectral efficiency improvements through AM-to-PM distortion correction while minimizing the increase in overall device complexity through shared components and coordinated control architecture.
Solution Approach 2:
The controller circuit is designed with multi-functionality, serving both amplitude control and phase control purposes. The same controller circuit that manages supply voltage adjustment for efficiency also implements phase correction for spectral efficiency, thereby achieving multiple functions without proportionally increasing complexity.
Data Source
AI summary
An RF power amplifier system comprises an amplitude control loop and a phase control loop. The amplitude control loop adjusts the supply voltage to the power amplifier based upon the amplitude correction signal indicating the amplitude difference between the amplitude of the input signal and an attenuated amplitude of the output signal. The phase control loop adjusts the phase of the input signal based upon a phase error signal indicating a phase difference between phases of the input signal and the output signal. The phase control loop may comprise one or more variable phase delays introducing a relative phase delay to allow the phase differences between the input and output signals of the PA circuit to be within a range compatible with a phase comparator generating the phase error signal, and a low frequency blocking module that removes the larger extent, lower frequency components of the phase error signal.