MOS Switch Gate Protection for High-Voltage Sampling Circuits
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Solution Overview
Problem
MOS transistors in switches 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 component 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 MOS transistor from overvoltage damage while allowing the switch to function properly
Solution Approach 2:
A discharge circuit is implemented to preliminarily discharge any voltage that may appear on the gate of the MOS transistor before it can cause damage. This discharge circuit activates when the diode prevents proper discharge, ensuring the gate voltage remains within safe limits before the MOS transistor operates
2Adaptability or versatility
If the voltage on the first node of the switch exceeds the maximum voltage withstood by the MOS transistor, then the switch can handle higher voltage applications, but the MOS transistor may be damaged and voltage sampling becomes distorted
Solution Approach 1:
Protective components (diode and discharge circuit) are implemented beforehand to cushion against potential overvoltage conditions. The diode provides continuous protection by clamping the gate voltage, while the discharge circuit provides backup protection, ensuring the MOS transistor remains intact even in high-voltage applications
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 ensuring accurate voltage sampling without distortion, even in 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
a discharge circuit coupling the first node with the first terminal, configured to conduct only when a voltage between the first node and the first terminal is greater than or equal to a threshold
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.