Browse Prior Art Database

Shared Sense Amplifier With Enhancement-Type Isolation Devices

IP.com Disclosure Number: IPCOM000119938D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Ueda, M: AUTHOR [+2]

Abstract

Disclosed is a shared sense amplifier for CMOS DRAMs, in which N-channel enhancement-type FETs controlled by level-shifted gate signals are used for isolation devices.

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This is the abbreviated version, containing approximately 67% of the total text.

Shared Sense Amplifier With Enhancement-Type Isolation Devices

      Disclosed is a shared sense amplifier for CMOS DRAMs, in
which N-channel enhancement-type FETs controlled by level-shifted
gate signals are used for isolation devices.

      Fig. 1 shows a CMOS DRAM with a shared sense amplifier, and
Fig. 2 shows the detail of the sense amplifier.  The memory is
assumed to operate with a 3.5 V internal power supply and have a 3.3
- 3.6 V bitline voltage swing.  When the left array is selected,
isolation devices T3 and T4 are cut off.  When the right array is
selected, isolation devices T1 and T2 are cut off.  At the time of
reading from the left array, the read signal must be transferred
through the isolation devices T3 and T4 to I/O.  In the prior art,
depletion-type FETs are used for the isolation devices to provide a
rapid data transfer. However depletion type FETs are not usually used
in CMOS DRAMs.

      In the present scheme, N-channel enhancement-type FETs are used
for the isolation devices.  The levels of the isolation signals ISOL
and ISOR are shifted from internal CMOS logic levels by logic level
converters such that their upper level is higher than the internal
power supply voltage and their lower level is higher than Vthn, where
Vthn is a threshold voltage of an N-channel FET.

      Fig.3 shows the logic level converter which converts the
isolation signal to a signal having an up level of 5 V and a down
level of 2 Vthn.  The up level i...