RF Amplifier Compression Control With Dynamic Supply Bias
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Solution Overview
Problem
Conventional RF PA systems face inefficiencies due to wide spectral occupancy and AM-to-PM distortion, especially under varying modulation techniques, and struggle to optimize power consumption while maintaining linear amplification, often relying on inefficient power supplies and requiring specialized PA designs or excluding SAW filters from correction loops.
Innovation Solution
A PA controller circuit with closed amplitude and phase control loops adjusts the supply voltage and phase of RF power amplifiers using amplitude and phase correction signals, employing switched mode power supplies and variable gain amplifiers to optimize efficiency and reduce spectral occupancy, while excluding SAW filters from the correction loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the output transistor is biased to remain linear at peak power transmitted, then linearity requirements are met, but power is wasted during off-peak amplitude periods
Solution Approach 1:
The patent applies dynamic biasing by varying the supply voltage to the output transistor according to the instantaneous amplitude of the RF input signal. The supply voltage controller adjusts the bias point dynamically, allowing the transistor to operate in saturation during peak power periods (improving efficiency) while maintaining acceptable linearity through feedback control. This resolves the contradiction by making the bias dynamic rather than fixed.
Solution Approach 2:
The patent changes the supply voltage parameter dynamically based on the RF signal amplitude. During peak power transmission, the supply voltage is increased to maintain linearity, while during off-peak periods, the supply voltage is reduced to save power. This parameter modulation resolves the contradiction between maintaining linearity and reducing power consumption.
2Use of energy by moving object
If EER technique is used to vary supply voltage based on amplitude signal, then efficiency gains are attempted, but the supply voltage cannot be varied in an energy-efficient way to accommodate large amplitude variations
Solution Approach 1:
The patent extracts the voltage conversion function from a complex wide-range converter and implements it using a simpler switched-mode power supply with variable duty cycle control. By separating the voltage adjustment function and controlling it through duty cycle modulation rather than requiring a complex wide-range converter, the system achieves efficiency gains while reducing the complexity of the voltage conversion mechanism.
Solution Approach 2:
The patent uses periodic switching action in the switched-mode power supply to adjust the supply voltage. The variable duty cycle control applies periodic switching at different duty ratios to achieve different average output voltages, providing an energy-efficient method to accommodate amplitude variations without requiring a complex continuous voltage converter.
3Ease of operation
If linear regulator is used to vary output voltage on fixed current load, then voltage adjustment is achieved, but power is consumed by the regulator itself when there is large drop in amplitude signal
Solution Approach 1:
The patent replaces the linear regulator (analog voltage adjustment mechanism) with a switched-mode power supply (digital switching mechanism). The switched-mode approach uses high-frequency switching and energy storage elements to achieve voltage adjustment with much lower power loss, substituting the inefficient linear regulation mechanism with a more efficient switching-based voltage conversion system.
4Object-affected harmful factors
If SAW filters are included in correction loop, then signal filtering is provided, but it becomes difficult to meet high bandwidth requirements for AM-to-PM correction
Solution Approach 1:
The patent extracts the SAW filter from the correction loop to eliminate its bandwidth-limiting effect. By removing the filtering function from the feedback path, the system can achieve the high bandwidth required for effective AM-to-PM distortion correction while still maintaining signal integrity through alternative means not dependent on the SAW filter in the correction loop.
Data Source
AI summary
An RF power amplifier system adjusts the supply voltage to the power amplifier based upon an amplitude correction signal indicating the amplitude difference between the amplitude of the RF input signal and an attenuated amplitude of the RF output signal of the power amplifier. A variable gain amplifier (VGA) adjusts the amplitude of the RF input signal, thus providing a second means of adjusting the amplitude of the output of the power amplifier. The gain of the VGA or the supply voltage to the power amplifier is controlled based on the AC components of the amplitude correction signal, while the DC components of the amplitude correction signal are blocked from controlling the VGA or the supply voltage to the power amplifier. The DC level of the gain control of the VGA, the average supply voltage to the power amplifier, or the closed loop gain of the overall amplitude correction loop is controlled separately by a compression control signal.