Op-Amp Constant Voltage Circuit for High-Frequency Noise Offset Control
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Solution Overview
Problem
In constant voltage generator circuits with differential amplifier feedback circuits, high-frequency noise outside the loop frequency band can cause differences in noise amplitude between inputs, leading to DC offset and malfunction, especially when phase compensation capacitance is used.
Innovation Solution
A constant voltage generator circuit with an operational amplifier and feedback circuit that includes a first resistor and an output transistor, where the operational amplifier generates a feedback voltage by dividing the output voltage between the output terminal and substrate voltage, and the output transistor controls the output voltage based on this feedback, effectively matching noise amplitudes between inputs and preventing DC offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If phase compensation capacitance is used in the feedback circuit to ensure stability, then feedback system stability is improved, but noise immunity deteriorates when high-frequency noise components are superimposed on substrate voltage potential, power supply, or output
Solution Approach 1:
A capacitor is introduced as an intermediary element connected between the inverting input terminal and the output terminal of the operational amplifier. This capacitor acts as a noise cancellation mechanism that specifically targets high-frequency noise components, allowing the feedback system to maintain stability while improving noise immunity. The capacitor mediates between the stable feedback loop and the noisy external environment.
2Reliability
If high-frequency noise components are superimposed on power supply or output, then noise amplitude difference is generated between inverting input and non-inverting input due to impedance difference, but this leads to DC offset generation and IC malfunction
Solution Approach 1:
The patent implements a feedback mechanism where a capacitor connects the output terminal back to the inverting input terminal of the operational amplifier. This feedback path allows the system to sense and counteract noise-induced voltage differences between the inputs. The feedback loop dynamically adjusts to cancel out the DC offset that would otherwise be generated by impedance differences during high-frequency noise events.
3Productivity
If general feedback circuit with loop frequency of several hundred kHz to several MHz is used, then constant voltage generation function is achieved, but the circuit remains vulnerable to high-frequency noise outside the loop frequency band
Solution Approach 1:
The patent modifies the frequency response characteristics of the feedback circuit by adding a capacitor in parallel with the feedback resistor. This parameter change creates a frequency-dependent feedback path that maintains the loop frequency for normal operation (several hundred kHz to several MHz) while introducing noise cancellation capability for high-frequency components outside the loop band. The capacitor's reactance changes with frequency, enabling selective noise rejection.
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
Prevents the generation of DC offset even when high-frequency noise components outside the loop frequency band are inputted, thereby preventing IC malfunction.
Implementation Method 1
The operational amplifier generates a feedback voltage generated by dividing an output voltage between an output terminal and a substrate voltage potential of the constant voltage generator circuit by the first resistor and a second resistor
Implementation Method 2
The operational amplifier is configured to amplify a voltage potential difference between a predetermined reference voltage and the feedback voltage and to output a control voltage
Implementation Method 3
The output transistor controls an output voltage based on the control voltage from the operational amplifier
Implementation Method 4
The feedback circuit is further configured to superimpose high-frequency noise components from the substrate voltage potential
Data Source
AI summary
A constant voltage generator circuit is provided with an operational amplifier including a feedback circuit having a first resistor, and transistor, and generates a feedback voltage generated by dividing an output voltage between an output terminal and a substrate voltage potential of the constant voltage generator circuit by the first resistor and a second resistor. The operational amplifier is configured to amplify a voltage potential difference between a reference voltage and the feedback voltage and to output a control voltage. The output transistor controls an output voltage based on the control voltage from the operational amplifier, and the feedback circuit is further configured to superimpose high-frequency noise components from the substrate voltage potential onto the feedback voltage.