Variable Gain Amplifier Feedback Stabilization for Constant Phase
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Solution Overview
Problem
Variable gain amplifier circuits face issues with phase characteristic distortion due to changes in feedback when adjusting gain, leading to signal waveform distortion.
Innovation Solution
Incorporating an adjustment resistor connected between the operational amplifier's inversion input terminal and the reference potential, whose resistance value is controlled to maintain a constant ratio with the combined resistance value of the input and feedback resistors, thereby stabilizing the feedback amount and phase characteristic during gain changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the input resistor value is changed to adjust gain, then the gain changes, but the phase characteristic varies and frequency at which phase slews shifts
Solution Approach 1:
A compensation capacitor is introduced as an intermediary element connected in parallel with the feedback resistor. This capacitor compensates for the phase shift caused by changing the input resistor value, thereby maintaining stable phase characteristics while allowing gain adjustment through input resistor variation.
Solution Approach 2:
The invention changes the electrical parameters (capacitance value) of the compensation capacitor to match different combinations of input and feedback resistors. By selecting appropriate capacitor values, the phase characteristic can be maintained constant across different gain settings, resolving the contradiction between gain adjustability and phase stability.
2Adaptability or versatility
If the feedback amount is changed to adjust gain, then the gain changes, but the amount of feedback from the operational amplifier varies
Solution Approach 1:
The compensation capacitor acts as a mediator that maintains consistent feedback amount by compensating for phase shifts. When the input resistor changes to adjust gain, the capacitor compensates for the resulting phase variation, ensuring the feedback amount remains stable and the operational amplifier operates consistently.
Solution Approach 2:
The compensation capacitor creates a feedback mechanism that counteracts the phase shift caused by input resistor changes. By introducing this capacitive feedback element, the circuit maintains stable phase characteristics and consistent feedback amount across different gain settings.
Data Source
AI summary
This variable gain amplifier is provided with an operational amplifier. The non-inversion input terminal of the operational amplifier is connected to a reference potential. A feedback resistor is connected between the output terminal and inversion input terminal of the operational amplifier. An input resistor is inserted between the inversion input terminal of the operational amplifier and the input terminal of the variable gain amplifier circuit. An adjustment resistor is connected between the inversion input terminal of the operational amplifier and the reference potential. The resistance value of the adjustment resistor is controlled in such a way as to maintain constant against the resistance value change a combined resistance value in its parallel connection with the input resistor when changing the resistance value of the input resistor.