The Metastable Behavior of a Schmitt-Trigger

Schmitt-Trigger circuits are the method of choice for converting general signal shapes into clean, well-behaved digital ones. In this context these circuits are often used for metastability handling, as well. However, like any other positive feedback circuit, a Schmitt-Trigger can become metastable...

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Bibliographic Details
Published in2016 22nd IEEE International Symposium on Asynchronous Circuits and Systems (ASYNC) pp. 57 - 64
Main Authors Steininger, Andreas, Maier, Jurgen, Najvirt, Robert
Format Conference Proceeding
LanguageEnglish
Published IEEE 01.05.2016
Subjects
Asynchronous
Context
Feedback circuits
Glitch
Hysteresis
Integrated circuit modeling
Late Transition
Mathematical model
Metastability
Negative feedback
Positive Feedback Circuit
Schmitt-Trigger
Threshold voltage
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Summary:Schmitt-Trigger circuits are the method of choice for converting general signal shapes into clean, well-behaved digital ones. In this context these circuits are often used for metastability handling, as well. However, like any other positive feedback circuit, a Schmitt-Trigger can become metastable itself. Therefore, its own metastable behavior must be well understood, in particular the conditions that may cause its metastability. In this paper we will build on existing results from Marino to show that (a) a monotonic input signal can cause late transitions but never leads to a non-digital voltage at the Schmitt-Trigger output, and (b) a non-monotonic input can pin the Schmitt-Trigger output to a constant voltage at any desired (also non-digital) level for an arbitrary duration. In fact, the output can even be driven to any waveform within the dynamic limits of the system. We will base our analysis on a mathematical model of a Schmitt-Trigger's dynamic behavior and perform SPICE simulations to support our theory and confirm its validity for modern CMOS implementations. Furthermore, we will discuss several use cases of a Schmitt-Trigger in the light of our results.
DOI:10.1109/ASYNC.2016.19