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CMOS Push Pull Dynamic Schmitt Trigger Circuit

IP.com Disclosure Number: IPCOM000050070D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Fifield, JA: AUTHOR [+3]

Abstract

A push pull dynamic Schmitt trigger circuit is provided in complementary metal oxide semiconductor (CMOS) technology which does not dissipate direct current power and which provides improved switching speed.

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CMOS Push Pull Dynamic Schmitt Trigger Circuit

A push pull dynamic Schmitt trigger circuit is provided in complementary metal oxide semiconductor (CMOS) technology which does not dissipate direct current power and which provides improved switching speed.

In the operation of the Schmitt trigger illustrated in the figure, when the voltage at the input goes up above a magnitude UTP, indicative of the upper trigger point, N channel transistor N1 turns on and the output switches toward ground with positive feedback through P channel transistor P3. The output is pulled high through transistors P1 and P2 when the input goes down below a magnitude or trigger point LTP, the lower trigger point. In this circuit, pull down is enhanced by the turn off of transistors P1 and P2, resulting in high speed switching. Pull up is enhanced due to the common source action of transistors P1 and P2, with transistor N3 providing feedback, while transistors N1 and N2 are turning off. Accordingly, it can be seen that the pull down and pull up in this circuit are due to similar device action and, therefore, complete symmetry may be obtained if the betas of the P channel transistors match the betas of the N channel transistors and the threshold voltage of the N channel transistors is equal to the absolute value of the threshold voltage of the P channel transistors.

It should be noted that direct current does not flow in the circuit when it is in its high or low state and the output logic win...