Bootstrap Switch I/O Protection Circuit for Overvoltage
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Solution Overview
Problem
Digital circuits face challenges in protecting their output terminals from overvoltage damage, as existing overvoltage-resistant output drivers occupy large area and have slower operating speeds, while overvoltage-resistant pass devices may not efficiently manage voltage levels.
Innovation Solution
A circuit configuration using a bootstrap switch with an N-channel metal-oxide semiconductor (NMOS) transistor, coupled with a capacitor and diode, where the output driver controls the pass-device to manage gate-source voltage and includes refresh circuitry to maintain voltage levels, ensuring efficient operation and protection from overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an overvoltage resistant output driver is used to protect the digital circuit, then the digital circuit is protected from overvoltage damage, but the driver occupies a relatively large area on the IC and has slower operating speeds
Solution Approach 1:
The output driver is segmented into two separate components: a standard-speed output driver and an overvoltage resistant pass device (transistor). The pass device is placed in series between the driver and the output terminal, creating a protective barrier without requiring the entire driver circuit to be overvoltage resistant. This segmentation allows the driver to maintain high speed while the pass device provides protection, resolving the contradiction between protection reliability and operating speed.
2Reliability
If an overvoltage resistant output driver is used to protect the digital circuit, then the digital circuit is protected from overvoltage damage, but the driver occupies a relatively large area on the IC
Solution Approach 1:
The output driver is segmented into two separate components: a standard-speed output driver and an overvoltage resistant pass device (transistor). The pass device is placed in series between the driver and the output terminal, creating a protective barrier without requiring the entire driver circuit to be overvoltage resistant. This segmentation allows the driver to maintain high speed while the pass device provides protection, resolving the contradiction between protection reliability and operating speed.
3Reliability
If an overvoltage resistant pass device is used to protect the lower voltage output driver, then the driver is protected from overvoltage, but additional circuitry or charge pumps are required which increase device complexity
Solution Approach 1:
The pass device gate is controlled directly by the output driver signal itself. When the driver outputs a logic high, the pass device turns on; when the driver outputs a logic low, the pass device turns off. This self-service control mechanism eliminates the need for separate control circuitry, charge pumps, or additional logic gates, thereby reducing device complexity while maintaining overvoltage protection functionality.
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 solution effectively protects digital I/O terminals from overvoltage while reducing current consumption and IC footprint, maintaining high operating efficiency and speed, unlike traditional methods that require additional circuitry or charge pumps.
Implementation Method 1
A digital zero from the output driver to the output terminal, may charge the capacitor. When the output driver sends a digital one to the output terminal, the charged capacitor, coupled between source and the gate of the NMOS transistor, is configured to provide sufficient gate-source voltage
Data Source
AI summary
A circuit to protect a digital input and output (I/O) terminal from an overvoltage applied externally to the digital I/O terminal. The circuit is arranged similar to a bootstrap switch such that a pass-device protects an output driver from an overvoltage applied to the digital I/O terminal and the output driver controls the operation of the pass-device, such as an N-channel metal-oxide semiconductor (NMOS) transistor. The circuit may include a capacitor and a diode coupled to the gate of the NMOS transistor. A digital zero from the output driver charges the capacitor. A digital one from the output driver causes the charged capacitor, coupled between source and the gate of the NMOS transistor, provides sufficient gate-source voltage to pass the digital one from the driver to the digital I/O terminal. The circuit further includes refresh circuitry configured to maintains the gate source voltage on the capacitor.