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Redundant Sense Sense Amplifier

IP.com Disclosure Number: IPCOM000107405D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Bunce, P: AUTHOR [+4]

Abstract

In a common base differential amplifier, the output level can be significantly affected by Vbe mistracking between the input sense transistors. In the prior art, the sense transistors, T501 and T502 in the figure, were the only devices used for sensing. (T501A and T502A were not present.) These devices were laid out in close proximity to each other in order to minimize the Vbe mistracking between devices. However, computer simulations have shown that even a minor mistracking in Vbe has a significant effect on the output differential of the sense amplifier. This is due to the relatively small input differential.

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Redundant Sense Sense Amplifier

       In a common base differential amplifier, the output level
can be significantly affected by Vbe mistracking between the input
sense transistors.  In the prior art, the sense transistors, T501 and
T502 in the figure, were the only devices used for sensing.  (T501A
and T502A were not present.)  These devices were laid out in close
proximity to each other in order to minimize the Vbe mistracking
between devices.  However, computer simulations have shown that even
a minor mistracking in Vbe has a significant effect on the output
differential of the sense amplifier.  This is due to the relatively
small input differential.

      In order to reduce the Vbe mistracking sensitivity of the
circuit, the Redundant Sense Sense Amplifier (RSSA) uses a parallel
combination of devices for each sense transistor. T501 and T501A are
laid out in close proximity to each other as are T502 and T502A.  The
resulting devices, T501/T502A and T502/T501A, yield improved Vbe
mistracking.  This improved mistracking comes about through the
multiplication of two statistical Gaussian distributions of Vbe (two
devices in parallel).  The resultant Vbe distribution is much
tighter.  Thereby, it allows the RSSA to provide a more uniform
output differential even at relatively low input levels.  Also, the
output is constant over a wider range of inputs, thus it enhances the
delay variation of the circuit significantly.