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CMOS Receiver Circuit with High Noise Margin

IP.com Disclosure Number: IPCOM000050688D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Bansal, JP: AUTHOR

Abstract

A CMOS receiver circuit is disclosed having a high noise margin not available in existing circuits. The circuit shown in the figure overcomes the problem in existing circuits that the input down level to the receiver circuit must be less than the threshold voltage minimum of the N channel device.

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CMOS Receiver Circuit with High Noise Margin

A CMOS receiver circuit is disclosed having a high noise margin not available in existing circuits. The circuit shown in the figure overcomes the problem in existing circuits that the input down level to the receiver circuit must be less than the threshold voltage minimum of the N channel device.

This problem is overcomes by the circuit shown in the above figure which uses one or two diodes (D1 and D2) between the ground reference potential and the source of the N channel FET device N1. The forward bias diode drop of D1 end D2 raises the source potential of the FET device N1. An additional N channel FET device N2 has its drain connected to the output node and its gate connected to the source of the FET device N1. As long as the input down level is less than the sum of the threshold voltage of the device N1 and the threshold voltage of the device N2, the N channel FET devices N1 and N2 will be off, the P channel FPT device P1 will be on, and the output level will be the drain potential V(DD).

When the input signal is at the up level or greater than thc sum of the threshold voltages of the FET devices N1 and N2, then the FETs N1 and N2 are on, the FET device P1 is off, and the output is equal to the source to drain voltage of the N2 device, which is equal to ground potential.

The diodes D1 and D2 provide the gate to source voltage which is greater than the threshold voltage of the FET device N2, and this insures that the...