Browse Prior Art Database

PROTECTION AGAINST ELECTRO STATIC DISCHARGE IN PAGERS

IP.com Disclosure Number: IPCOM000006868D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-07
Document File: 2 page(s) / 147K

Publishing Venue

Motorola

Related People

Hossein Kasmai: AUTHOR

Abstract

When the Electra Static Discharge is applied to the enclosed pager, it will enter the enclosure through the open gaps. These open gaps may be found in places such as around the buttons, on the comers where the top and bottom part of the enclosure meet and most importantly around the programming pins. Since these pins are completely exposed, they provide a great path for the charges to enter the pager enclosure.

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INC. Technical Developments Volume 19 June 1993

PROTECTION AGAINST ELECTRO STATIC DISCHARGE IN PAGERS

by Hossein Kasmai

   When the Electra Static Discharge is applied to the enclosed pager, it will enter the enclosure through the open gaps. These open gaps may be found in places such as around the buttons, on the comers where the top and bottom part of the enclosure meet and most importantly around the programming pins. Since these pins are completely exposed, they provide a great path for the charges to enter the pager enclosure.

  The charges enter the pager only to fmd their path out and tinally exit the pager into the ground plane. Since the enter gap and the exit gap for the charges may be located on the opposite sides of the enclosure, the shortest path found (path with least impedence) may be through the internal circuitry, in which case a sot? or hard failure may result. The input pins of the microcontroller or any other I.C. are not capable of withstanding such large amounts of energy and therefore must be protected. A protection circuitry at the inputs of the device may help solve the problem but has negative factors such as: 1) cost increase 2) part count 3) functionality sacrifice of the circuit, such as progr-abiity or receiver sensitivity.

  The objective of using spark gaps is to provide a bypass path for the Electra Static Discharges, without using additional parts in order to avoid further damage to the pager. Since the p.c. board is layed out such that the internal ground path is found mostly around the board, it can provide an excellent path for the charges entering and exiting the enclosure. By running an unmasked ground trace near all enclosure gaps, around all buttons or any other sensitive area where there is a high possibility of charges entering, the entering charges will arc into the ground trace. At this point the ground traces will provide a low impedence path for the charges to find the exit gap and leave the pager without any dam- age. See Figure 2 for more details.

When the progr amming pins are subjected to Electra Static Discharges, the damage to the circuitry may be

more crucial due to the lack of insulation on these pins. The spark gap me...