Output Circuit Virtual Ground Layout for Stable 0 V Linearity
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Solution Overview
Problem
Existing output circuits struggle to maintain linearity of output voltage with respect to input voltage, especially around 0 V, due to unstable negative feedback loops and difficulty in generating accurate 0 V output voltages.
Innovation Solution
The output circuit incorporates a configuration with diodes between a ground node and a virtual ground terminal, allowing the generation of output voltage with reference to the virtual ground, which is higher than the ground voltage, and includes a resistor R4 to ensure a current path for the output transistor even at 0 V, stabilizing the negative feedback loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the output circuit uses a conventional configuration with operational amplifier and three-terminal regulator, then the circuit can output 0 V, but the linearity of output voltage with respect to input voltage is not maintained over the entire range
Solution Approach 1:
The patent segments the ground reference into two distinct levels: actual ground (0 V) and virtual ground (e.g., 2.5 V). This segmentation allows the output transistor to operate around the virtual ground level, maintaining stable negative feedback loop operation while achieving accurate 0 V output at the actual output terminal. The segmentation resolves the contradiction by separating the feedback stability requirement from the output voltage requirement.
Solution Approach 2:
The patent introduces a virtual ground as an intermediary reference level between the actual ground and the power supply voltage. This virtual ground serves as a mediator that allows the negative feedback loop to operate stably with a non-zero reference voltage, while the output circuit can still produce accurate 0 V output. The intermediary virtual ground enables both stable feedback operation and accurate zero output simultaneously.
2Measurement precision
If the output transistor is turned off to output 0 V, then the output voltage can be 0 V, but the negative feedback loop becomes unstable
Solution Approach 1:
The patent creates an equipotential virtual ground node that maintains a constant voltage level (e.g., 2.5 V) relative to actual ground. By operating the output transistor around this equipotential virtual ground level rather than actual ground, the transistor remains in a stable active region even when the output voltage needs to be 0 V. This equipotential approach maintains feedback loop stability while achieving accurate zero output.
Solution Approach 2:
The patent changes the reference voltage parameter from 0 V (actual ground) to a non-zero value (virtual ground, e.g., 2.5 V). This parameter change allows the output transistor to operate with a non-zero gate-source voltage even when the output voltage is 0 V, keeping the transistor in a stable active state and maintaining negative feedback loop stability while achieving accurate zero output.
3Reliability
If the virtual ground is set higher than actual ground, then the negative feedback loop stability is improved, but the circuit complexity increases
Solution Approach 1:
The virtual ground node serves multiple functions simultaneously: it provides a stable reference voltage for the negative feedback loop, enables accurate 0 V output, and acts as an operating point for the output transistor. By making the virtual ground multi-functional, the patent achieves improved feedback stability without proportionally increasing circuit complexity, as the same virtual ground node performs multiple critical roles.
Solution Approach 2:
The patent uses the virtual ground as an equipotential reference that simplifies the overall circuit analysis and design. By establishing a clear virtual ground potential level, the circuit becomes more systematic and easier to design, offsetting the apparent complexity increase with improved design methodology and reduced operational complexity.
Data Source
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AI summary
An output circuit (10) according to the present invention includes a first output terminal (VO) and a second output terminal (SGND); an output transistor (MP1) connected between a first fixed-potential node (VCC) and the first output terminal; an output load (15) connected between the first output terminal and the second output terminal; a control circuit (13) that controls the output transistor so that a monitor voltage (VS) based on a voltage between the first output terminal and the second output terminal matches an input voltage (VI); a constant voltage source (16) whose one end is connected to the second terminal and whose other end is connected to a second fixed-potential node (GND); and a circuit (R4) that forms a current path between the first output terminal and the second fixed-potential node. Accordingly, in the output circuit, stability of a negative feedback loop can be enhanced, and linearity of an output voltage with respect to an input voltage can be enhanced.