Power Amplifier Supply Control Using Distortion Feedback
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Solution Overview
Problem
Conventional RF power amplifier systems face inefficiencies due to fixed biasing during off-peak RF signal amplitudes, leading to wasted power and increased spectral occupancy, with existing techniques like EER and polar modulation failing to provide significant energy efficiency gains, and the need for adaptive supply voltage adjustments to accommodate varying output power and impedance changes.
Innovation Solution
A power amplifier controller circuit that measures distortion levels and adjusts the supply voltage to maintain optimal efficiency by comparing measured distortion to a target level, using a distortion measurement module and comparator to adjust the supply voltage, ensuring minimal power consumption while maintaining acceptable distortion levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the output transistor is biased to remain linear at peak power transmitted, then the distortion is reduced and linearity is improved, but power is wasted during off-peak periods when the bias remains fixed
Solution Approach 1:
The patent applies dynamic biasing by adjusting the output transistor's bias point in real-time according to the instantaneous amplitude of the RF input signal. During peak power transmission, the bias is set to maintain linearity and minimize distortion. During off-peak periods, the bias is reduced to minimize power consumption. This dynamic adjustment resolves the contradiction between maintaining linearity and reducing power waste.
Solution Approach 2:
The patent changes the bias parameter of the output transistor dynamically based on the RF signal amplitude. By modulating the bias voltage or current according to the signal envelope, the system achieves optimal linearity during peak power while minimizing power consumption during low-power periods, thus resolving the contradiction between linearity and power efficiency.
2Loss of energy
If the supply voltage is reduced to improve efficiency, then power consumption is reduced, but distortion increases and spectral occupancy widens
Solution Approach 1:
The patent dynamically adjusts the supply voltage to the power amplifier based on the instantaneous signal amplitude and distortion measurements. When the RF signal is at peak power, the supply voltage is maintained at a higher level to ensure low distortion and acceptable spectral occupancy. When the signal is at off-peak levels, the supply voltage is reduced to minimize power consumption. This dynamic voltage adjustment resolves the contradiction between power consumption and distortion control.
Solution Approach 2:
The patent employs a feedback mechanism where the distortion level of the amplified signal is measured and used to adjust the supply voltage. The system continuously monitors distortion and adjusts the supply voltage to maintain distortion below a threshold while maximizing efficiency. This feedback control resolves the contradiction by automatically balancing power consumption and distortion levels.
3Loss of energy
If conventional EER technique is used to vary supply voltage based on amplitude signal, then some efficiency gain is achieved, but significant efficiency gains are not realized due to difficulty in realizing fast accurate voltage converter
Solution Approach 1:
The patent extracts only the necessary function of voltage conversion without implementing a complex wide-range voltage converter. Instead of using a conventional EER approach that requires a fast, accurate, wide-range voltage converter, the system uses a simplified voltage adjustment mechanism that operates effectively within the required range, reducing device complexity while maintaining efficiency gains.
Solution Approach 2:
The patent replaces the complex, expensive wide-range fast voltage converter with a simpler, more economical voltage adjustment circuit. The simplified circuit may have limited range or speed compared to a full EER implementation but provides sufficient performance for the application at much lower complexity and cost, effectively trading off unnecessary capabilities for practical efficiency improvements.
Data Source
AI summary
A power amplifier controller measures the distortion of a power amplifier output. Based upon the distortion measured, the supply voltage to the PA is adjusted in a control loop. In one embodiment, distortion is measured by computing the ratio of the measured power in the output frequencies outside the desired output channel to the measured power in the output frequencies within the desired channel. If the distortion measured from the PA is higher than a target distortion level, the power supply voltage is raised. If the distortion measured from the PA is lower than the target distortion level, the power supply voltage is reduced. Thus, the supply voltage to the PA is maintained at the lowest possible voltage level, improving the efficiency of the PA.