Feedback Amplifier Gain Control Using Segmented Feedback Resistance
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Solution Overview
Problem
Feedback amplifiers in optical communication systems face challenges in arbitrarily controlling gain when the difference in input signal is large, as they rely solely on the turn-on resistance of the feedback transistor for gain control.
Innovation Solution
An automatic gain control feedback amplifier is designed with a feedback resistor unit whose total resistance value is determined by control signals, incorporating a bias circuit and phase compensating circuit to adjust resistance values and control gain arbitrarily, even with varying input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If gain control is achieved using only the turn-on resistance of the feedback transistor, then the circuit structure remains simple, but the gain cannot be arbitrarily controlled when the difference in input signal is large
Solution Approach 1:
The feedback resistor is divided into multiple segments (first feedback resistor and second feedback resistor) that can be selectively connected to the input terminal through switching transistors. This segmentation allows different resistance values to be applied based on input signal conditions, enabling arbitrary gain control while maintaining a relatively simple overall circuit structure.
Solution Approach 2:
The feedback resistance value is made dynamic by using control signals to selectively connect different feedback resistor segments based on the input signal level. When the input signal exceeds a threshold, the switching transistors change the feedback resistance value, allowing the gain to be arbitrarily controlled according to input signal conditions rather than being fixed by a single resistance value.
2Adaptability or versatility
If an additional gain control signal generating circuit is configured to supply control signals, then arbitrary gain control becomes possible, but the device complexity increases
Solution Approach 1:
The switching transistors serve dual functions: they act as part of the amplification circuit and simultaneously function as gain control switches by selectively connecting different feedback resistor segments. This multi-functionality eliminates the need for separate gain control signal generating circuits, achieving arbitrary gain control while avoiding additional circuit complexity.
Solution Approach 2:
The gain control function is merged with the existing amplification circuit structure. The control signals are integrated into the feedback path, and the switching transistors are combined with the feedback resistor network, creating a unified circuit that performs both amplification and gain control without requiring separate dedicated control circuits.
Data Source
AI summary
Disclosed is an automatic gain control feedback amplifier that can arbitrarily control a gain even when a difference in input signal is large. The automatic gain control feedback amplifier includes: an amplification circuit unit configured to amplify voltage input from an input terminal and output the amplified voltage to an output terminal; a feedback circuit unit connected between the input terminal and the output terminal and including a feedback resistor unit of which a total resistance value is determined by one or more control signals and a feedback transistor connected to the feedback resistor unit in parallel; and a bias circuit unit configured to supply predetermined bias voltage to the feedback transistor.