Schmitt Trigger Pull-Up Topology for High-Voltage Fast Switching
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Solution Overview
Problem
Designing a Schmitt trigger that operates at high switching speeds while also functioning at high supply voltages poses a challenge, as it can be difficult to protect the transistors from damage.
Innovation Solution
A Schmitt trigger design incorporating a feedforward connection and a pull-up transistor to ensure the selected node is maintained at a high enough reference voltage for proper operation while preventing transistor damage, using a pass transistor to prevent high supply voltage from reaching the second inverter and a pull-up transistor to maintain sufficient voltage for switching in both high and low voltage modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high supply voltages are used to ensure proper operation of the Schmitt trigger, then the switching reliability is improved, but the transistors may be damaged due to excessive voltage
Solution Approach 1:
A clamp circuit is introduced as an intermediary component between the supply voltage source and the Schmitt trigger transistors. This clamp circuit includes a clamp transistor and clamp resistor that work together to limit the voltage reaching the transistors to a safe level, thereby protecting them from damage while still allowing the Schmitt trigger to operate reliably at high supply voltages.
Solution Approach 2:
The invention dynamically controls the voltage parameter delivered to the transistors by using the clamp circuit to adjust the effective voltage level. The clamp transistor switches between conducting and non-conducting states to regulate the voltage, ensuring it remains within safe operating limits while maintaining high supply voltage operation for reliable switching.
2Speed
If small transistors are used to enable high-frequency operation, then the switching speed is improved, but the transistors become more susceptible to voltage damage
Solution Approach 1:
The clamp circuit serves as a protective intermediary that specifically safeguards small, high-speed transistors from voltage damage. By placing the clamp transistor and resistor in series with the supply voltage, the circuit limits the maximum voltage exposure to these vulnerable but high-performance transistors, enabling them to operate at high frequencies without risk of overvoltage damage.
3Reliability
If the Schmitt trigger is designed to operate at high supply voltages, then the noise immunity is improved, but the circuit complexity increases due to protective components
Solution Approach 1:
The clamp circuit is designed with minimal components (one transistor and one resistor) to provide comprehensive voltage protection. This simple intermediary structure adds negligible complexity to the Schmitt trigger while effectively enabling high supply voltage operation for improved noise immunity and overall reliability.
Data Source
AI summary
An integrated circuit includes an input pad and a Schmitt trigger coupled to the input pad. The Schmitt trigger includes a first inverter and a second inverter. The Schmitt trigger includes a pull-up transistor coupled to an input of the second inverter and configure to supply a high reference voltage to the input of the second inverter.