Class AB Output Stage Feedback for Stable Gain and Impedance
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Solution Overview
Problem
The operational amplifier with a class AB amplifier of source follower type experiences significant variation in voltage gain and output impedance due to the transistor connected to the output terminal being switched ON and OFF based on the load-driving current, compromising the stability of the negative feedback circuit.
Innovation Solution
A class AB amplifier design with a gain control amplifier that maintains the first and second nodes at equal voltage, ensuring the fourth transistor remains ON, thereby stabilizing the voltage gain and output impedance regardless of the load-driving current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a class AB amplifier of source follower type is used at the output stage, then output impedance is suppressed, but voltage gain and output impedance vary significantly with load-driving current
Solution Approach 1:
A gain control amplifier is introduced to detect the output impedance variation and provide feedback control. The gain control amplifier monitors the voltage at the output terminal and adjusts the gate voltage of the fourth transistor to maintain constant voltage gain and output impedance, thereby stabilizing the negative feedback circuit.
Solution Approach 2:
The invention dynamically changes the gate-source voltage of the fourth transistor based on the load-driving current conditions. By adjusting this voltage parameter, the transistor operates in different regions (linear or saturation) to maintain stable voltage gain and output impedance across varying load conditions.
2Use of energy by moving object
If a transistor is switched ON and OFF based on load-driving current, then power consumption is reduced, but voltage gain and output impedance vary significantly
Solution Approach 1:
The invention dynamically adjusts the operating state of the fourth transistor rather than simple ON/OFF switching. The gain control amplifier continuously modulates the gate voltage to keep the transistor in an optimal operating region, maintaining stable electrical characteristics while adapting to varying power consumption requirements.
Solution Approach 2:
The gain control amplifier provides continuous feedback control to maintain stable voltage gain and output impedance. It detects variations in the output characteristics and adjusts the transistor's gate voltage accordingly, ensuring stable operation across different power consumption states.
3Stability of the object's composition
If the fourth transistor is kept ON at all times, then voltage gain and output impedance remain stable, but power consumption increases
Solution Approach 1:
The invention changes the operating parameters (gate-source voltage) of the fourth transistor to maintain it in a controlled ON state. By adjusting the voltage parameter dynamically, the transistor remains conductive with optimized current flow, maintaining stable output impedance while reducing unnecessary power consumption compared to a always-full ON state.
Solution Approach 2:
The gain control amplifier provides feedback to maintain the fourth transistor in a stable ON state with optimized current. It continuously monitors the output characteristics and adjusts the gate voltage to keep the transistor conducting at the optimal level, balancing stability and power consumption.
Data Source
AI summary
A second main electrode of a first transistor is connected to a first main electrode of a sixth transistor, a second main electrode of the sixth transistor is connected to a first main electrode of a fifth transistor at a first node, a second main electrode of the fifth transistor is connected to a second main electrode of a second transistor, a control electrode of the fifth transistor is connected to the second main electrode of the fifth transistor, a second main electrode of a third transistor is connected to a first main electrode of a fourth transistor at a second node, and a control electrode of the fourth transistor is connected to the control electrode of the fifth transistor. A gain control amplifier controls a voltage supplied to a control electrode of the sixth transistor such that the first node and the second node are equal in voltage.