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Logical Technique for Reducing the Delta-I Noise Caused by Simultaneous Switching of Off-Chip Drivers

IP.com Disclosure Number: IPCOM000119605D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Rizzolo, RF: AUTHOR [+3]

Abstract

Most high performance Very Large-Scale Integration (VLSI) technologies limit the number of off-chip drivers which may switch simultaneously. This limit is imposed because transient switching currents may add and cause excessive noise on the power supplies. A technique to decrease this noise by creating a balanced data bus precharge state is shown.

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Logical Technique for Reducing the Delta-I Noise Caused by Simultaneous
Switching of Off-Chip Drivers

      Most high performance Very Large-Scale Integration (VLSI)
technologies limit the number of off-chip drivers which may switch
simultaneously.  This limit is imposed because transient switching
currents may add and cause excessive noise on the power supplies.  A
technique to decrease this noise by creating a balanced data bus
precharge state is shown.

      This technique is to precharge the data bus to a state where
one half of the outputs are high and one half are low. From this
state, a maximum of one half of the bus can switch in any one
direction.  The whole bus can switch (from the precharge to the
precharge-not state), but, in this case, half switch up and the other
half switch down which essentially cancels the delta-I noise.  Most
technologies have rules that govern how effective this cancellation
is.  Upon entering the precharge state, another simultaneous switch
occurs, but again a maximum of half the bus switches in either
direction.

      In order to force a precharge state, a bus precharge signal
must become active for some time before the data to be gated is
valid.  The removal of this precharge signal gates valid data to the
bus (Precharge = Gate).  Fig. 1 shows a trigger clock starting the
logic propagation to the bus drivers.  In general, there may be
multiple paths to the drivers which may lead to multiple switch
conditions signi...