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Protecting Chip Cards Against Electrostatic Discharge

IP.com Disclosure Number: IPCOM000041849D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Proebster, WE: AUTHOR [+2]

Abstract

It is proposed that a chip card be protected against electrostatic discharge (ESD) by short-circuiting the chip contacts at times at which the card is neither read nor written. A chip card is a data carrier in the general shape of a credit card and comprises one or more integrated circuit (IC) chips for logic and/or memory functions. Similar to credit cards, chip cards will become objects of daily use and thus must be readily usable. For this purpose, the logic chip of the card must be protected against destruction or undesired changes of the written information by electrostatic discharge. The I/O pads of the FET chips are protected by what are known as ESD diodes which are generally special devices with a low breakdown voltage to the substrate.

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Protecting Chip Cards Against Electrostatic Discharge

It is proposed that a chip card be protected against electrostatic discharge (ESD) by short-circuiting the chip contacts at times at which the card is neither read nor written. A chip card is a data carrier in the general shape of a credit card and comprises one or more integrated circuit (IC) chips for logic and/or memory functions. Similar to credit cards, chip cards will become objects of daily use and thus must be readily usable. For this purpose, the logic chip of the card must be protected against destruction or undesired changes of the written information by electrostatic discharge. The I/O pads of the FET chips are protected by what are known as ESD diodes which are generally special devices with a low breakdown voltage to the substrate. These ESD diodes protect the chip only against potentials between the I/O pads and the substrate. However, depending upon the process for which they are employed, such devices are often reduced in their effectiveness. In most cases, this poses no serious problems, as FET chips, after their manufacture, are permanently mounted on the modules or cards and thus are much better protected against external static charges than chip cards with bare contacts that are touched by hand or carried in a pocket or the like. In such cases, there is the risk of a potential building up between the various card connections, against which the ESD devices would be ineffective. Therefore, it is proposed that the chip card be protected against destruction of the written information or the devices by external electrostatic charges. For this purpose, all card contacts are electrically short-circuited. This short-circuiting is effective only at times at which the card is neither written nor read. As soon as operating voltages are applied, the short-circuiting is automatically suspended. For implementing this proposal, two basically different electrical approaches, as described below, are feasible. 1. Implementation without electrical control A chain of...