Bootstrapping Switch Pull-Down Circuit for Voltage Overstress Protection
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Solution Overview
Problem
Conventional bootstrapping switches in communication devices, such as analog-to-digital converters, suffer from premature device aging and failure due to voltage overstress, leading to issues like hot carrier injection and dielectric breakdown, especially when handling high input voltages.
Innovation Solution
The implementation of a bootstrapping switch with a diode-connected MOS transistor in the pull-down path, coupled with additional protection transistors, ensures that the gate terminal is protected from excessive voltages, allowing for quick transitions between ON and OFF states without performance degradation, using a combination of diode-connected and parallel protection devices to mitigate voltage overstress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional bootstrapping switches handle high input voltages, then signal sampling capability is improved, but device aging accelerates and reliability deteriorates due to voltage overstress
Solution Approach 1:
A protection transistor is introduced as an intermediary element between the bootstrapping switch and the high voltage input signal. This protection transistor acts as a mediator that limits the voltage stress on the bootstrapping switch by conducting excess current when voltage exceeds safe levels, thereby enabling the switch to handle high input voltages without suffering from accelerated aging and reliability degradation
2Reliability
If protection devices are added to prevent voltage overstress, then reliability is improved, but device complexity increases
Solution Approach 1:
The protection transistor is merged with the existing bootstrapping switch structure, sharing common nodes and integrating seamlessly into the switch's operational flow. This merging approach allows the protection function to be added without requiring entirely separate protection circuits, thereby limiting the increase in device complexity while still achieving reliable voltage overstress protection
Data Source
AI summary
Methods and systems for reliable bootstrapping switches may comprise sampling a received signal with a bootstrapping switch, where the bootstrapping switch comprises a switching metal-oxide semiconductor (MOS) transistor having a pull-down path coupled to a gate terminal of the switching MOS transistor, wherein: source terminals of both a diode-connected transistor and a second MOS transistor are coupled to the gate terminal of the switching MOS transistor; drain terminals of both the diode-connected transistor and the second MOS transistor are coupled to a source terminal of a third MOS transistor, the third MOS transistor coupled in series with a fourth MOS transistor; and a drain terminal of the fourth MOS transistor is coupled to ground. The third and fourth MOS transistors may be in series with the second MOS transistor. A gate terminal of the fourth transistor may be switched from ground to a supply voltage to activate the pull-down path.