MOS Sampling Switch With Gate Clamp for Overvoltage Protection
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Solution Overview
Problem
MOS transistors in electronic circuits face issues when the voltage on their first node exceeds the maximum voltage they can withstand, leading to potential damage and distortion in voltage sampling circuits.
Innovation Solution
A switch design incorporating a MOS transistor with a diode coupling the first terminal to the gate, a capacitive element, and a discharge circuit to manage voltage thresholds, along with additional MOS transistors and resistors to prevent excessive voltage differences, ensuring safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MOS transistor is used as a switch to transmit voltage, then the switch can effectively transmit the voltage present on the first node to the second node, but the voltage on the first node may exceed the maximum voltage the MOS transistor can withstand, causing potential damage
Solution Approach 1:
A diode is introduced as an intermediary element between the first node and the gate of the MOS transistor. The diode couples the first node to the gate, preventing the gate voltage from exceeding the source voltage by more than a diode drop, thereby protecting the transistor from excessive voltage differences while allowing high voltage transmission through the drain-source path.
Solution Approach 2:
The discharge circuit is configured to activate when the voltage between the first node and first terminal exceeds a threshold level. This preliminary protection mechanism clamps the voltage difference before it can reach dangerous levels that would damage the MOS transistor, ensuring the transistor operates within safe voltage limits.
2Reliability
If additional protection circuits are added to prevent overvoltage damage, then the MOS transistor is protected from damage, but the circuit complexity and number of components increase
Solution Approach 1:
The diode serves as a simple intermediary protection element that limits the maximum voltage difference between gate and source to approximately one diode forward voltage drop. This single component provides effective protection without requiring complex voltage regulation or multiple protection devices.
Solution Approach 2:
The discharge circuit utilizes the inherent capacitance of the gate and the diode's voltage-clamping特性 to automatically limit voltage excursions. The circuit self-regulates the gate voltage based on the first node voltage, eliminating the need for external control circuits or additional active protection components.
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
The design maintains safe voltage differences across the MOS transistor, preventing damage and maintaining accurate voltage transmission, suitable for high-voltage applications.
Implementation Method 1
a diode coupling the first terminal with the first node
Implementation Method 2
a capacitive element coupling a third terminal of the switch with the first node
Implementation Method 3
the discharge circuit comprises two Zener diodes series connected and reverse connected with respect to each other
Data Source
AI summary
In an embodiment a switch includes a first MOS transistor having its source connected to its channel-forming region and coupled with a first terminal of the switch, its drain coupled with a second terminal of the switch, and its gate connected to a first node of the switch, a diode coupling the first terminal with the first node, a capacitive element coupling a third terminal of the switch with the first node, the third terminal being configured to receive a control signal for the switch and a discharge circuit coupling the first node with the first terminal, the discharge circuit configured to conduct only when a voltage between the first node and the first terminal is greater than or equal to a threshold.