Variable Gate Clamp Circuit for NMOS Stress Testing
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Solution Overview
Problem
Designing driver circuits with NMOS power transistors poses challenges in ensuring accurate gate clamp voltage, particularly in normal operation and stress testing modes, as existing solutions either result in overly complex circuits or inadequate protection due to variations in temperature and process corners.
Innovation Solution
A driver circuit with a variable gate clamping mechanism that adjusts clamp voltage based on a reference voltage, using a combination of current sources and transistors to provide both normal and stress testing modes, ensuring robust operation and protection without impacting normal functioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an inaccurate gate clamp is used, then the clamp voltage exhibits a wide operating voltage range due to temperature and process corner variation, but the variation may overlap into normal working range and extend past the absolute maximum rating of the transistor device
Solution Approach 1:
The gate clamp circuit transitions from a static design to a dynamic one by enabling/disabling the clamp circuit based on operational mode. A mode selection circuit dynamically controls the clamp circuit's enable signal, allowing the clamp voltage to be adjusted between normal operation and stress testing modes, thus resolving the contradiction between adaptability and reliability
Solution Approach 2:
The patent changes the operational parameters of the clamp circuit by controlling its enable/disable state through a mode selection circuit. This parameter change allows the same hardware to provide different clamp voltage characteristics suitable for different operational modes, ensuring both protection during normal operation and compatibility with stress testing
2Measurement precision
If an accurate gate clamp is used, then the clamp voltage is accurate, but the circuit design becomes overly complex due to the need for implementing extra circuitry with extra bias current on the output
Solution Approach 1:
The gate clamp circuit is designed to serve multiple functions: it provides accurate voltage clamping during normal operation and simultaneously supports stress testing operations. By making the clamp circuit multi-functional through mode selection, the patent avoids the need for separate dedicated circuits, thereby reducing overall complexity while maintaining accuracy
Solution Approach 2:
The same gate clamp circuit serves both normal operation and stress testing needs through self-configuration based on mode selection. The circuit automatically adjusts its behavior (enabled or disabled) based on the operational mode, eliminating the need for additional dedicated stress testing circuitry and reducing overall system complexity
3Adaptability or versatility
If complex circuits are used to disconnect driver control circuitry from the gate terminal during stress testing, then stress testing can be performed, but the circuit complexity increases
Solution Approach 1:
The patent merges the stress testing functionality with the existing gate clamp circuit rather than implementing a separate disconnection mechanism. The mode selection circuit integrates control of the clamp circuit into the existing driver architecture, combining multiple functions (clamping and stress testing support) into a unified system that reduces overall complexity
Data Source
AI summary
A generator circuit is coupled to apply a control signal to the gate terminal of a power transistor driving an output node. A reference voltage is generated having a first voltage value as the reference for the control signal and having a second, higher, voltage value for use in stress testing. A clamping circuit is provided between the reference voltage and the power transistor gate to function in two modes. In one mode, the clamping circuit applies a first clamp voltage to clamp the voltage at the gate of the power transistor when the generator circuit is applying the control signal. In another mode, the clamping circuit applies a second, higher, clamp voltage to clamp the gate of the power transistor during gate stress testing.