Operational Amplifier Common-Mode Feedback for Power Noise Rejection
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Solution Overview
Problem
Conventional infrared signal processing circuits face challenges in improving power-source noise canceling characteristics without reducing dynamic range, particularly in low-voltage operations, due to the influence of power source noise in operational amplifier circuits.
Innovation Solution
The implementation of an operational amplifier circuit with a transconductance amplifier circuit, common-mode feedback circuit, and a voltage supply circuit that maintains a differential output voltage level equal to a reference voltage unaffected by power source voltage, while supplying power source voltage from a terminal to each circuit, thereby enhancing power-source noise canceling characteristics without significantly reducing the dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a constant voltage circuit is used to supply reference voltage to the transconductance amplifier, then power-source noise canceling characteristics are improved, but dynamic range is reduced
Solution Approach 1:
The power supply system is segmented into two independent parts: (1) a constant voltage circuit that generates a noise-immune reference voltage for the transconductance amplifier, and (2) a separate power source voltage supply for the operational amplifier circuit. This segmentation allows the reference voltage to be isolated from power-source noise while the operational amplifier retains full dynamic range by directly receiving the power source voltage.
Solution Approach 2:
A constant voltage circuit acts as an intermediary between the power source and the transconductance amplifier. It converts the noisy power source voltage into a clean reference voltage that is insensitive to power-source noise, thereby improving noise canceling characteristics without forcing the operational amplifier to operate from a reduced voltage level.
2Object-affected harmful factors
If the output voltage of the constant voltage circuit is used as power source voltage for the transconductance amplifier, then power-source noise canceling characteristic is improved, but dynamic range is reduced by the difference between vdd and vref
Solution Approach 1:
The power supply architecture is divided into two independent channels: the reference voltage channel (through the constant voltage circuit) and the power source voltage channel (directly from vdd). This segmentation eliminates the voltage drop penalty (vdd−vref) from affecting the operational amplifier's dynamic range while maintaining the noise-canceling benefits in the reference voltage channel.
Solution Approach 2:
The constant voltage circuit serves as an intermediary only for generating the reference voltage, not for powering the operational amplifier. This allows the operational amplifier to receive full power source voltage directly, preserving its dynamic range while the intermediary constant voltage circuit provides noise-immune reference voltage to the transconductance amplifier.
3Loss of energy
If operational amplifier circuit operates at low voltage to meet battery-driven requirements, then power consumption is reduced, but sufficient dynamic range cannot be ensured
Solution Approach 1:
The circuit parameters are optimized to enable low-voltage operation: the transconductance amplifier is designed with appropriate gm values and the operational amplifier is sized to maintain sufficient gain and bandwidth at low supply voltages. This allows the circuit to operate at low voltage (reducing power consumption) while still achieving the required dynamic range through parameter optimization rather than voltage scaling.
Data Source
AI summary
An operational amplifier circuit includes a transconductance amplifier circuit which converts a differential input voltage into a differential output current; a common-mode feedback circuit which outputs a control signal to the transconductance amplifier circuit 1 so as to make a D.C. voltage level of a differential output voltage of the transconductance amplifier circuit equal to a reference voltage; a voltage supply circuit which supplies a reference voltage to the common-mode feedback circuit; and an output load to which the differential output voltage of transconductance amplifier circuit is applied, and which constitutes an output terminal of the operational amplifier circuit 5. A power source voltage is supplied to each of the circuits. The operational amplifier circuit has an improved power-source noise canceling characteristic while maintaining its dynamic range.