Static information storage and retrieval – Read/write circuit – Data refresh
Patent
1997-05-19
1999-05-11
Nelms, David C.
Static information storage and retrieval
Read/write circuit
Data refresh
365201, G11C7/00
Patent
active
059035056
ABSTRACT:
A method for testing refresh operations of a memory array wherein subthreshold leakage current may be set to near worst-case conditions. The memory array includes a first row of memory cells having a first memory cell configured to store a first memory value, and a second row of memory cells having a second memory cell configured to store a second memory value. The method comprises storing a logic high value to the first memory cell as the first memory value, followed by storing a logic low value to the second memory cell as the second memory value. The method further comprises repeatedly driving a write bit line coupled to both the first and second memory cells at a logic low level for a period of a time equal to a refresh interval corresponding to the first memory cell. Additionally, the method includes subsequently reading the first memory value from the first memory cell. Finally, the method includes indicating that the first memory cell is operating correctly if the first memory value is still equal to a logic high value, or indicating that the first memory value is malfunctioning if the first memory value is equal to a logic low value. Driving the write bit line low may be accomplished by repetitively reading the second memory cell. The same effect may alternately be achieved by repetitively writing a logic low value to the second memory cell. By keeping the write bit line at a logic low level during testing of refresh operations, the subthreshold leakage current through the write transistor of the first memory cell may be increased. This accelerates the discharge of the first memory value, and insures testing is performed near worst-case conditions.
REFERENCES:
patent: 5566117 (1996-10-01), Okamura et al.
Phan Tuan
Trieu Thien
Wik Thomas R.
Kivlin B. Noel
LSI Logic Corporation
Nelms David C.
Phan Trong
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