Emitter Follower Amplifier Stages for Feedback Impedance Stability
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Solution Overview
Problem
Conventional amplifying circuits experience gain fluctuations due to impedance changes in the negative feedback circuit, limiting their operation and stability, especially in current feedback amplifiers and differential amplifier circuits.
Innovation Solution
The proposed amplifying circuit employs a first stage with emitter follower circuits and transistors configured to increase input impedance, allowing for stable operation and reduced gain fluctuations by determining collector currents based on power source potentials and resistor values, and includes a suppression circuit to stabilize transistor operating points and reduce feedback circuit impedance contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a negative feedback circuit is connected to an operational amplifier, then the amplifier can function as an inverting or non-inverting amplifier circuit, but the gain fluctuates according to the impedance of the feedback circuit
Solution Approach 1:
The invention divides the amplifier into multiple independent stages (first stage amplifying circuit, second stage amplifying circuit, third stage amplifying circuit), where each stage has its own feedback circuit. This segmentation isolates the feedback impedance effects to individual stages, preventing them from affecting the overall gain stability of the entire amplifier system.
Solution Approach 2:
The invention introduces intermediate buffer circuits between stages that act as mediators. These buffer circuits have high input impedance and low output impedance, which isolates the feedback circuits from each other and from the input signal source, thereby preventing impedance interactions that would cause gain fluctuations.
2Reliability
If a constant current source is used in a differential amplifier circuit, then the collector currents are limited to a lower current, but the operation is not limited by feedback circuit impedance
Solution Approach 1:
The invention replaces static constant current sources with dynamic current supply circuits that can adaptively provide higher currents when needed. The current supply circuits are designed to respond to signal demands while maintaining operational stability, allowing collector currents to exceed the limitations of traditional constant current sources.
Solution Approach 2:
The invention changes the operating parameters of the transistors by removing the constant current constraints. This allows the collector currents to be determined by the signal requirements and circuit configuration rather than being fixed by constant current sources, thereby increasing power capability while maintaining stability through the multi-stage architecture.
3Reliability
If emitter follower circuits are added to increase input impedance, then gain fluctuations are suppressed, but the device complexity increases
Solution Approach 1:
The invention designs each amplifying stage to perform multiple functions simultaneously. The transistors in each stage serve as both the amplifying element and the input impedance boosting element through their inherent emitter follower configuration. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity.
Data Source
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AI summary
The first emitter follower circuit and the second emitter follower circuit can increase an input impedance on the side of the inverting input terminal in the amplifying circuit. As a result, when a feedback circuit is connected between the inverting input terminal and the output terminal of the amplifying circuit, a fluctuation in a gain of the amplifying circuit according to a configuration of the feedback circuit can be suppressed.