Feedback Amplifier Bias Switching for Faster RX Stabilization
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Solution Overview
Problem
Existing high-frequency amplifiers, such as low noise amplifiers in radio communication devices, take longer than desired to reach a stable state after switching from transmission to reception mode due to the feedback path between the output and input terminals, which affects the stability of DC voltage nodes and thereby prolongs the 'guard time' between transmission and reception operations.
Innovation Solution
Incorporating a switch that temporarily lowers the resistance value between the output node for the gate bias voltage and a node in the feedback path, allowing the gate bias voltage to be applied directly to a node in the feedback path, thereby reducing the time required for the amplifier to reach a stable operating state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a feedback path is provided between the output terminal and the input terminal to match impedance and lower noise figure, then the noise figure is reduced and impedance matching is improved, but the time required to reach a stable state after bias voltage is applied increases
Solution Approach 1:
The feedback path is segmented into two branches: one branch contains the feedback resistor for DC bias feedback, and the other branch contains the series combination of feedback resistor and capacitor for AC signal feedback. This segmentation allows the DC and AC feedback paths to be independently optimized, enabling faster stabilization while maintaining noise figure performance.
Solution Approach 2:
A capacitor is introduced as an intermediary element in the feedback path. The capacitor blocks DC components while allowing AC signal components to pass through the feedback path. This intermediary element enables the feedback resistor to provide DC bias stabilization without directly affecting the AC signal feedback, thereby reducing the time to reach stable state while maintaining noise figure benefits.
2Reliability
If a feedback path with given resistance value is provided to match input impedance to output impedance, then impedance matching is improved for maximum power transfer, but the stability time of DC voltage nodes increases
Solution Approach 1:
The feedback path is divided into separate DC and AC feedback branches. The DC feedback branch provides impedance matching for maximum power transfer, while the AC feedback branch (with capacitor) provides rapid signal feedback. This segmentation allows the DC voltage to stabilize faster while maintaining impedance matching reliability.
Solution Approach 2:
The feedback path parameters are changed by introducing a capacitor in series with one branch of the feedback network. This parameter change creates frequency-dependent feedback characteristics: at DC, the feedback resistor dominates for impedance matching, while at AC frequencies, the capacitor enables faster signal feedback, thereby reducing the stability time of DC voltage nodes.
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 solution enables the amplifier to reach the operating state in a shorter time, allowing for a reduction in the 'guard time' between transmission and reception operations, thereby improving the signal-to-noise ratio and efficiency in radio communication devices.
Implementation Method 1
a feedback path coupled to the input terminal and the output terminal and including a resistor and a capacitor
Data Source
AI summary
An amplifier including a first transistor including a gate coupled to an input terminal and a grounded source; a load resistor provided between a drain of the first transistor and a power supply; an output terminal coupled to a node between the drain of the first transistor and the load resistor; a feedback path coupled to the input terminal and the output terminal and including a resistor and a capacitor; a bias voltage generator applying a gate bias voltage to the gate of the first transistor in response to an enable signal; a supply resistor provided between an output node for the gate bias voltage of the bias voltage generator and the gate of the first transistor; and an enable switch lowering a resistance value between the output node for the gate bias voltage and a node in the feedback path.