Static information storage and retrieval – Floating gate – Particular biasing
Reexamination Certificate
2001-07-31
2003-11-04
Mai, Son (Department: 2818)
Static information storage and retrieval
Floating gate
Particular biasing
C365S185200
Reexamination Certificate
active
06643178
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to sensing circuits for use in a memory device, and more particularly, to a source side sensing circuit for use in a memory device.
BACKGROUND OF THE INVENTION
For low voltage operation of a memory device, for example a “Flash” memory device, a sensing circuit is used to sense core cell current to determine memory data values. However, typical sensing circuits may have problems providing enough usable gain, and as a result, it may difficult to accurately determine memory data values.
FIG. 1
shows a conventional sensing circuit
100
for use with a memory device. A core cell current (I
0
) derived from a core cell
102
is sensed by a resistor
104
. The current appears as a voltage (SAIn) that is coupled to a comparator
106
and compared to a reference signal. The comparator
106
produces a core cell data value as a result of the comparison. The fixed resistor
104
is used to convert the core cell current I
0
to a voltage for comparison.
FIG. 2
shows another conventional sensing circuit
200
for use with a memory device. The core cell current I
0
is coupled to a drain of transistor
202
. During operation, when the transistor is turned off, the SAIn node starts increasing in voltage. The SAIn voltage will be dependant on the core cell data.
Unfortunately these conventional sensing circuits may have problems providing enough gain or voltage differential on the SAIn terminal for accurate comparison. Therefore is would be desirable to have a sensing circuit that overcomes the problems associated with conventional sensing circuits.
SUMMARY OF THE INVENTION
The present invention includes a system for source side sensing in a memory device. The system includes a constant current source to determine a core cell current and a cascode circuit to convert the core cell current to an output voltage. The output voltage is used to compare to a reference signal to determine the data value of the memory cell.
In one embodiment of the invention, a source side sensing circuit for use in a memory device to determine core cell data from core cell current is provided. The source side sensing circuit includes a constant current source coupled to receive the core cell current, and a cascode circuit coupled to the constant current source to convert the core cell current to an output voltage that is representative of the core cell data.
In another embodiment of the invention, a method for source side sensing a core cell current in a memory device is provided. The method includes steps of coupling the core cell current to constant current source, coupling a cascode current provided by a cascode circuit to the constant current source, and converting the cascode current to an output voltage that is representative of the core cell current.
REFERENCES:
patent: 5555217 (1996-09-01), Hashimoto
patent: 5757697 (1998-05-01), Briner
patent: 5986937 (1999-11-01), Yero
patent: 6191979 (2001-02-01), Uekubo
patent: 6292395 (2001-09-01), Lin
patent: 6510082 (2003-01-01), Le et al.
Fujitsu Limited
Mai Son
Sheppard Mullin Richter & Hampton LLP
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