Dynamic Bias Power Amplifier for Flat Gain Linearity
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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 to generate a gain deviation signal, allowing the bias driver to adjust the bias of the power amplifier stage to maintain a flat gain profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the power amplifier is biased at a relatively large quiescent current to achieve needed 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 condition (higher quiescent current) and a second bias condition (lower quiescent current) based on the operating state. The bias control circuit dynamically adjusts the bias voltage to the power amplifier stage, transitioning from a static bias approach to a dynamic one that adapts to power level changes, thereby resolving the contradiction between maintaining linearity and improving efficiency during power-back-off.
Solution Approach 2:
The patent changes the bias voltage parameter dynamically based on operating conditions. The bias control circuit monitors the operating state and adjusts the bias voltage accordingly - maintaining a higher bias voltage for linearity when needed, and reducing it during power-back-off to improve efficiency. This parameter change strategy allows the system to optimize both linearity and efficiency at different operating points.
2Device complexity
If the power amplifier operates with static bias to simplify the circuit, then device complexity is reduced, but soft compression region causes degraded adjacent channel leakage ratio linearity
Solution Approach 1:
The patent implements feedback control where the bias control circuit monitors the operating state of the power amplifier and adjusts the bias voltage accordingly. This feedback mechanism detects when the amplifier enters a soft compression region and responds by adjusting the bias condition to maintain linearity and improve adjacent channel leakage ratio, thereby resolving the contradiction between circuit simplicity and linearity performance.
Solution Approach 2:
The patent transitions from static bias to dynamic bias control, where the bias conditions can change based on operating requirements. The bias control circuit enables dynamic switching between different bias states to prevent soft compression and maintain optimal linearity performance, accepting increased circuit complexity as a trade-off for improved performance.
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 voltage parameter dynamically based on operating conditions. The bias control circuit monitors the operating state and adjusts the bias voltage accordingly - maintaining a higher bias voltage for linearity when needed, and reducing it during power-back-off to improve efficiency. This parameter change strategy allows the system to optimize both linearity and efficiency at different operating points without unnecessarily reducing power.
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.