Power Amplifier Bias Control for Flat Gain Under Soft Compression
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Solution Overview
Problem
Traditional power amplifiers with static bias circuits face inefficiencies during power-back-off operations and exhibit degraded linearity due to soft compression regions, limiting their ability to achieve both high linear power levels and efficiency.
Innovation Solution
A power amplifier system with dynamic bias circuitry and bias control circuitry that includes a compression sensor and a bias driver to adjust the bias of the power amplifier stage, maintaining a flat gain profile and extending the linear region of operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the power amplifier is biased at a relatively large quiescent current to achieve linearity, then linearity is improved, but efficiency deteriorates during power-back-off operation
Solution Approach 1:
The patent applies dynamic biasing by switching between a first bias current (higher current for linearity) and a second bias current (lower current for efficiency) based on the operating power level. This dynamic adjustment resolves the contradiction by adapting the bias current to the actual power output requirements, maintaining linearity when needed while reducing energy consumption during power-back-off operation.
2Device complexity
If the power amplifier operates with static bias, then device simplicity is maintained, but the soft compression region degrades adjacent channel leakage ratio linearity
Solution Approach 1:
The patent introduces dynamic bias switching that adjusts the bias current based on the power output level. This dynamic approach extends the linear region of operation by preventing the soft compression effect that occurs with static bias, thereby improving adjacent channel leakage ratio linearity without significantly increasing device complexity.
3Measurement precision
If the power amplifier is backed down further in power to achieve required linearity, then linearity is improved, but efficiency deteriorates
Solution Approach 1:
The patent changes the bias current parameter dynamically based on the power output level. By switching between a first bias current (higher) and a second bias current (lower), the system maintains linearity at high power levels while improving efficiency at lower power levels, eliminating the need to back down power to achieve linearity.
Data Source
AI summary
A power amplifier system having a power amplifier stage with dynamic bias circuitry is disclosed. Also included is bias control circuitry having a compression sensor having a sensor input coupled to a RF signal output and a sensor output, wherein the compression sensor is configured to generate a gain deviation signal in response to a sensed deviation from a flat gain profile of the power amplifier stage. Further included is a bias driver that is configured to drive dynamic bias circuitry to adjust bias to the power amplifier stage to maintain the flat gain profile in response to the gain deviation signal.