Automotive Sensor EMC ESD Protection Circuit Design
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Solution Overview
Problem
Conventional automobile sensor devices face challenges with electromagnetic compatibility (EMC) and electrostatic discharge (ESD) resistance due to electromagnetic noise from engine and starter units, leading to radio frequency voltage excitation and potential device breakdown, as well as static electricity application that can break the resistance element in the EMC resistance improvement circuit.
Innovation Solution
The solution involves connecting diode elements in series between the output terminal and the ground terminal in opposite directions and adding a capacitance element between the resistance element and the ground terminal, which helps in preventing voltage clamping during electromagnetic interference and limits high voltage application from static electricity, ensuring accurate signal reading and preventing resistance element breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional EMC resistance improvement circuit with a resistance element and capacitance element is used, then electromagnetic compatibility resistance is improved, but electrostatic discharge resistance deteriorates because the resistance element breaks under high static voltage
Solution Approach 1:
A diode element is introduced as an intermediary protective component between the output terminal and ground terminal. The diode clamps high voltage transients caused by electrostatic discharge, preventing the resistance element from breaking while maintaining the EMC filtering function of the original circuit.
Solution Approach 2:
The diode element is positioned to provide beforehand protection against electrostatic discharge. It is configured to conduct and clamp voltage before the resistance element can be damaged by high static voltage, thus cushioning the resistance element from harmful effects.
2Manufacturing precision
If the insulating film is thinned for finer integrated circuits, then manufacturing precision and integration are improved, but withstand voltage decreases making the resistance element more susceptible to breakage
Solution Approach 1:
The diode element serves as an intermediary protective barrier that compensates for the reduced withstand voltage capability of thinned insulating films. By clamping voltage excursions before they reach the resistance element, the diode enables the use of thinner insulating films without compromising reliability.
3Reliability
If diode elements are added for ESD protection, then electrostatic discharge resistance is improved, but voltage clamping during electromagnetic interference causes signal reading errors
Solution Approach 1:
The reverse breakdown voltage of the diode element is carefully selected to be higher than the maximum expected signal voltage but lower than the electrostatic discharge voltage. This parameter selection allows the diode to protect against ESD while remaining non-intrusive during normal signal operation, preventing false clamping of valid signals.
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 provides a sensor device with enhanced EMC and ESD resistance, allowing accurate signal reading and preventing device malfunction, while enabling a thinner insulating film for finer integrated circuits and improved power dissipation, thus reducing size and improving performance.
Implementation Method 1
diode elements (9, 10) connected between the output terminal (11) and the ground terminal (3) and connected to each other in series in opposite directions to each other
Implementation Method 2
capacitance element (7) connected between a side of the resistance element (8) closer to the signal processing integrated circuit (5) and the ground terminal (3)
Data Source
Figure 1~4
Figure 5~7
Figure 8~10
AI summary
In conventional sensor devices, it has been difficult to achieve both EMC resistance and ESD resistance, which are required at the output terminals of an automobile sensor device. A sensor device 1 of the present embodiment comprises: a power supply terminal 2 that supplies power; a ground terminal 3; a sensor element 4, the electrical characteristics of which change in accordance with a physical quantity; a signal processing integrated circuit 5 that processes an output signal output from the sensor element 4; and an output terminal that outputs the output signal processed by the signal processing integrated circuit 5. In addition, the signal processing integrated circuit 5 comprises: a signal processing circuit 6 that processes the output signal output from the sensor element 4; a resistance element 8 that is connected between the output terminal 11 and the signal processing circuit 6, and that is disposed on an insulating film; diode elements 9, 10 that are connected between the output terminal 11 and the ground terminal 3, and that are serially connected with each other in opposite directions; and a capacitance element 7 that is connected between the ground terminal 3 and the signal processing circuit 6 side of the resistance element 8.