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Browse Prior Art Database

Improved Decoupled Memory Card

IP.com Disclosure Number: IPCOM000105601D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Coteus, PW: AUTHOR [+3]

Abstract

It is well known that good immunity to power plane noise is required in DRAM memory cards. As the speed of memory chips increases, this requirement becomes even more important. It has become common practice to locate thin decoupling capacitors underneath the DRAM memory chips, between the power and ground pins of the chip package. The reason for locating the capacitors under the memory chips is that the path length, and thus the inductance, for the power and ground leads of the memory chip is shortened. The effectiveness of the capacitor in suppressing unwanted noise on the power plane is inversely dependent on the inductance between the capacitor and the chip devices consuming the power.

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This is the abbreviated version, containing approximately 76% of the total text.

Improved Decoupled Memory Card

      It is well known that good immunity to power plane noise is
required in DRAM memory cards.  As the speed of memory chips
increases, this requirement becomes even more important.  It has
become common practice to locate thin decoupling capacitors
underneath the DRAM memory chips, between the power and ground pins
of the chip package.  The reason for locating the capacitors under
the memory chips is that the path length, and thus the inductance,
for the power and ground leads of the memory chip is shortened.  The
effectiveness of the capacitor in suppressing unwanted noise on the
power plane is inversely dependent on the inductance between the
capacitor and the chip devices consuming the power.

      With the use of thin small outline packaged (TSOP) memory
chips, it is no longer possible to place the capacitors underneath
the memory chips, since the free space between the memory chip and
circuit card is of order 50 microns.  The result is that the
capacitors must be located further from the memory chips.  The result
is that card size grows, and the decoupling is degraded.  Fig. 1
shows a typical memory card, termed a SIMM for Single Inline Memory
Package, constructed of memory chips and decoupling capacitors
located above them.  Note that the lead configuration of the memory
chips used is such that the 2 center leads on each side of the chip
are missing.  This forms a natural cavity when chips are placed in a
line.  Fig...