Dynamic Bias Control in RF Amplifiers for Low-Idle Linearity
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Solution Overview
Problem
Conventional radio frequency amplifiers experience linearity degradation when operating conditions are shifted closer to class B from class A and idle currents are reduced, leading to upward gain swing at high input power.
Innovation Solution
The amplifier incorporates a bias current subtracting circuit and a bias current adding circuit, both in current mirror relationships, to dynamically adjust the bias current based on signal amplitude, with the subtracting circuit dominant in the linear region and the adding circuit dominant in the saturation region, using transistors and a current source to offset and adjust the bias current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the bias current is increased to suppress gain compression and improve saturation power, then high saturation power is achieved, but power consumption increases due to higher idle current
Solution Approach 1:
The patent implements dynamic bias current adjustment by introducing a bias control circuit that modifies the bias current based on the input signal amplitude. The bias current is increased only when needed (at high input powers approaching saturation) rather than maintaining a high constant bias current, thereby achieving saturation power improvement without continuous power consumption penalty. This is accomplished through detectors that sense input power levels and control circuits that adjust bias accordingly.
Solution Approach 2:
The patent changes the bias current parameter dynamically based on operating conditions. By using detection circuits to monitor input power levels and adjusting the bias current parameter in response, the system transitions from a static high bias current approach to a dynamic parameter adjustment approach. This allows the amplifier to operate with lower idle current while maintaining performance at high power levels.
2Use of energy by moving object
If the idle current is reduced to lower power consumption by operating closer to class B, then power consumption decreases, but linearity degrades due to upward gain swing at high input power
Solution Approach 1:
The patent employs feedback mechanisms where detectors monitor the input signal amplitude and feed this information back to the bias control circuit. The bias control circuit then adjusts the bias current in response to the detected signal level. This feedback loop ensures that when the amplifier approaches saturation (which would cause gain compression and linearity degradation), the bias current is increased to maintain linearity, even though the amplifier operates in class B or AB mode for power efficiency.
Solution Approach 2:
The patent performs preliminary action by detecting the input signal amplitude before significant distortion occurs and proactively adjusting the bias current to prevent linearity degradation. The bias control circuit anticipates the need for bias adjustment by monitoring signal levels and modifying the bias current in advance, preventing the upward gain swing that would otherwise occur at high input powers.
3Power
If a conventional bias control circuit is used to increase bias current for saturation power improvement, then saturation power increases, but the circuit complexity increases and cannot simultaneously optimize both linearity and power efficiency
Solution Approach 1:
The patent segments the bias control function into distinct components: detection circuits that sense input power levels, control circuits that process the detection signals, and bias adjustment circuits that modify the bias current. This segmentation allows each component to perform its specific function efficiently and enables modular design, reducing overall circuit complexity while achieving the desired performance improvements in saturation power and linearity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration suppresses linearity degradation even when idle current is reduced, improving gain flatness over a wide input power range by decreasing bias current in the linear region and increasing it in the saturation region.
Implementation Method 1
when power of a radio frequency input signal increases, a drain current of the input power detecting FET increases as a result of rectifying the radio frequency signal
Data Source
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AI summary
There has been a problem that linearity is degraded in the conventional amplifier when the idle current is reduced in order to lower the power consumption. An amplifier of the present invention includes: a bias circuit to cause a bias current to flow; an amplifying element to amplify a signal by causing an output current corresponding to the bias current to flow; a bias current subtracting circuit to detect the signal and subtract, from the bias current, a current based on an amplitude of the signal detected; and a bias current adding circuit having an operation starting point higher than an operation starting point of the bias current subtracting circuit, and to detect the signal and add, to the bias current, a current based on an amplitude of the signal detected.