Semiconductor Output Circuit Noise Suppression via Back Gate Impedance
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Solution Overview
Problem
Semiconductor devices used in vehicle-mounted systems face noise resistance issues due to induced noise from other devices or wiring, which can cause malfunctions in output circuits, especially when long output wiring is involved.
Innovation Solution
Incorporating a second circuit with impedance of a predetermined value between the back gate and power source of a transistor in the output circuit to suppress noise frequencies, preventing errors in the output signal by reducing charge injection from the power source during noise induction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MOSFET is provided between input terminal and ground terminal with bias voltage applied to gate and back gate, then the drain potential is clamped to bias voltage using parasitic diode, but induced noise from long output wiring causes malfunction of output circuit
Solution Approach 1:
A second circuit (resistor) is introduced as an intermediary element between the back gate and power source. This resistor acts as a mediator that limits charge injection from the power source to the back gate during noise induction, thereby suppressing the harmful effects of induced noise on the output circuit while maintaining the clamping function of the parasitic diode.
Solution Approach 2:
The impedance of the back gate circuit is changed by introducing a resistor with a specific impedance value (100Ω to 10kΩ). This parameter change modifies the electrical characteristics of the back gate, reducing its susceptibility to noise-induced charge injection from the power source while maintaining proper biasing and clamping functionality.
2Length of stationary object
If long output wiring is used to transmit analog voltage to ECU, then signal transmission distance is increased, but induced noise from other devices or wiring is applied to output wiring
Solution Approach 1:
The second circuit (resistor) serves as an intermediary that decouples the back gate from direct power source connection. This intermediary structure reduces the coupling between power source noise and the sensitive back gate, enabling the system to tolerate longer output wiring lengths without suffering from excessive induced noise interference.
Solution Approach 2:
The parasitic diode, which could potentially conduct noise current, is converted into a beneficial element by using its clamping characteristic in combination with the high-impedance back gate circuit. The diode clamps the drain potential to the bias voltage, while the resistor limits charge injection, together transforming the parasitic structure into a noise-suppression mechanism.
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
This configuration effectively improves noise resistance in semiconductor devices and sensor systems, preventing malfunctions caused by induced noise and ensuring reliable operation in vehicle-mounted applications.
Implementation Method 1
The second circuit is provided between the back gate and a power source and has impedance of a predetermined value or more for suppressing noise of a predetermined frequency generated at the input terminal
Data Source
AI summary
Provided are a semiconductor device and a sensor system capable of achieving improvement of noise resistance. Thus, an output circuit 106a in the semiconductor device includes: input terminals 207n, 207p; and an output terminal 208; an output amplifier 201 connecting the input terminals 207n, 207p to the output terminal 208; a feedback element 203 returning the output terminal 208 to the input terminal 207n; a switching transistor 204; and a resistance element 206. A drain of the switching transistor 204 is connected to the input terminal 207n. The resistance element 206 is provided between a back gate of the switching transistor 204 and a power source Vdd and has impedance of a predetermined value or more for suppressing noise of a predetermined frequency generated at the input terminal 207n.