Browse Prior Art Database

Bit switch in semiconductor memory Disclosure Number: IPCOM000013777D
Original Publication Date: 2000-Jul-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 5 page(s) / 59K

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Bit switch in semiconductor memory

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Bit switch in semiconductor memory

Bit switch in semiconductor memory

     Disclosed is a circuit of bit switch in
semiconductor memory for reducing rush current and
power consumption by using read and write control
signals. Reduced rush current leads to a stable
operation of peripheral components and itself.

     A semiconductor memory has bit switches to
read data from and write data to memory cells. A
bit line connects to plural memory cells. The bit
switches locate between data lines and bit lines.
They connect required number of bit lines to data
lines. In read and write operation of a dynamic
random access memory (DRAM) and a static random
access memory (SRAM), the bit switch usually
connects one bit line to one data line. In search
operation of a content addressable memory (CAM), it
usually connects plural bit lines to one data line.

     Figure 1 shows a circuit schematic including
a conventional bit switch. The bit switch (TN2/TN3)
and a pre-charging device (TN0/TN1) use only
N-MOSFETs (NFETs) because the logic high voltage
level of a bit line (BLT/BLC) and a data line
(DLT/DLC) is limited to Vdd - Vtn, where Vdd means
power supply voltage and Vtn means threshold
voltage of NFET, in order to reduce current
consumption. The bit switch connects the bit line
to the data line in read, write and search
operation. The pre-charging device pulls the bit
line up to Vdd - Vtn. The P-MOSFET (PFET), TP0,
equalizes BLT and BLC. A data line pre-charge
circuit not shown here pre-charges DLT and DLC up
to Vdd - Vtn. BLPCEQBSN controls the bit switch
devices. When it is high, the pre-charging device
pre-charges the bit line up to Vdd - Vtn and a
inverter, I0, forces EQNBS low. The bit switch is
off to isolate the bit line and the data line. When
BLPCEQBSN goes low, EQNBS goes high and the bit
switch turns on to connect the bit line and the
data line.

     In read operation, small read signal on the
pair of bit lines must go fast through the bit
switches to be amplified by a data line sense
amplifier, therefore the bit switch devices need to
be low-resistive, i.e., wide enough when they are
N-MOSFETs. In write and search operation, a data
line driver circuit not shown here pu...