Browse Prior Art Database

Fabrication of a Bilevel Clamp

IP.com Disclosure Number: IPCOM000086892D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Battista, MA: AUTHOR [+4]

Abstract

Described is a single transistor device which may be used to limit both positive and negative voltage reflections on unterminated transmission lines connecting semiconductor chips. Fig. 1 shows a circuit schematic of the device. Fig. 2 shows a topographic view of the important masking steps to fabricate the device, and Fig. 3 illustrates the vertical cross section.

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Fabrication of a Bilevel Clamp

Described is a single transistor device which may be used to limit both positive and negative voltage reflections on unterminated transmission lines connecting semiconductor chips. Fig. 1 shows a circuit schematic of the device. Fig. 2 shows a topographic view of the important masking steps to fabricate the device, and Fig. 3 illustrates the vertical cross section.

The diode D1 is formed by the base-emitter junction of the device. The emitter, which becomes the cathode, is tied to +V voltage supply on the chip. The base, which is also shorted to the collector, is the anode. A resistor R1, about 50 ohms, may be integrated into the device (Figs. 2 and 3) by extending the collector region. This resistor serves to limit the current which passes through the clamp diode. By connecting the far end of this resistor to the chip pad, the voltage at the pad is limited to about a diode voltage above the +V level.

It can be seen from Fig. 3 that another diode D2 is formed by the junction of the collector-subcollector and the substrate. Since the substrate is tied to the most negative voltage (typically ground), this diode forms a clamp which limits the negative voltage at the chip pad to about a diode voltage below ground.

The significant features of this device are:

1. It offers a method of limiting voltage reflections

on the transmission lines which connect the chips.

High voltage reflections could cause component

damage and/or degrade the spe...