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Fast Driver with Transistor Clamp

IP.com Disclosure Number: IPCOM000107414D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 3 page(s) / 78K

Publishing Venue

IBM

Related People

Wong, RC: AUTHOR

Abstract

Large swing word line drivers (Fig. 1) have been used for the HARPNP memory arrays. The Word Line (WL) pull up is accomplished initially with the Darlington drive of Td and T7, and subsequently with the Emitter Follower drive of T7. The Drain Line (DL) pull down is accomplished with the collector drive of T9. With this circuit configuration, a fast swing of about 2.0 volts is provided within a power supply of 3.6 volts, with no need of PNP pull ups. However, as operation temperature reaches beyond 75~C, circuit performance quickly degrades. Since the Vf of the SBD clamps S4 and S5 is approaching the Vbe of T5 and T9, the switching transistors T5 and T9 are getting saturated. Also, at high temperatures, the DL down level needs to be raised so that the chance of the HARPNP cell breakdown can be minimized.

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Fast Driver with Transistor Clamp

       Large swing word line drivers (Fig. 1) have been used for
the HARPNP memory arrays.  The Word Line (WL) pull up is accomplished
initially with the Darlington drive of Td and T7, and subsequently
with the Emitter Follower drive of T7. The Drain Line (DL) pull down
is accomplished with the collector drive of T9.  With this circuit
configuration, a fast swing of about 2.0 volts is provided within a
power supply of 3.6 volts, with no need of PNP pull ups.  However, as
operation temperature reaches beyond 75~C, circuit performance
quickly degrades.  Since the Vf of the SBD clamps S4 and S5 is
approaching the Vbe of T5 and T9, the switching transistors T5 and T9
are getting saturated.  Also, at high temperatures, the DL down level
needs to be raised so that the chance of the HARPNP cell breakdown
can be minimized.  To overcome these problems, the SBD clamps are
replaced by transistor clamps as shown in Fig. 2.  T5 is clamped by
TY to a Vce of about 0.3 volt, while T9 is clamped by TZ to
a Vce of about .4 volt.  The exact levels are controlled by the IR
drops through R3 and R5.  Since transistor clamps track with the
switching transistors, this circuit will remain fast even at much
higher temperatures.  The DL down level also remains higher to
maintain a sufficient margin from the HARPNP cell breakdown.  These
transistor clamps are used mainly to extend the circuit operation to
higher temperatures. However, nominal array per...