US6256755B1
Expired / Lapsed
US
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Apparatus and method for detecting defective NVRAM cells
Assignee: International Business Machines Corp
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Filing: 1998-10-19
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Granted: 2001-07-03
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Expires: 2018-10-19
Abstract
Abstract An apparatus and method for detecting a defective array of NVRAM cells. A counter is provided which times an erase time interval for the NVRAM cells during a regular erase function. The computed erase interval is compared with a maximum erase interval to determine at least a first characteristic which indicates the block of NVRAMs is at the end of its useful life. A second characteristic is determined by computing the slope in the erase time function versus the number of simulated erase functions. When the slope of the erase function exceeds a maximum slope, the NVRAM array is determined to be at the end of its useful life.
Inventors
- 👤 Terence B. Hook
- 👤 Chung H. Lam
- 👤 Eric S. Lee
- 👤 James S. Nakos
- 👤 Nivo Rovedo
- 👤 Richard Q. Williams
- 👤 Robert C. Wong
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 06:58
CPC Classifications
G; G11; G11C; G11C16/00; G11C16/02; G11C16/06; G11C16/34; G11C16/349; G11C16/3495; G11C29/00; G11C29/04; G11C29/50; G11C29/50004; G11C29/50012; G11C16/04
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
39 words
A method for detecting the end of the life of an NVRAM array comprising: determining an erase time function for said NVRAM array; and determining from a characteristic of said function when said NVRAM is susceptible to imminent failure.
Claim 2
Independent Claim
39 words
A method for detecting the end of the life of an NVRAM array comprising: determining an erase time function for said NVRAM array; and determining from a characteristic of said function when said NVRAM is susceptible to imminent failure.
Claim 3
Dependent Claim
20 words
The method according to claim 1 wherein said characteristic is the most recent time of erasure for said NVRAM array.
Claim 4
Dependent Claim
15 words
The method according to claim 1 wherein said characteristic is the slope of said function.
Claim 5
Dependent Claim
48 words
The method for detecting, the end of the life of an NVRAM ray according to claim 1 wherein said erase time function is determined by monitoring, the threshold voltage of each NVRAM cell and measuring the time it takes said threshold voltage to reach a predetermined reference value.
Claim 6
Independent Claim
51 words
A method for determining the end of useful life for an NVRAM array comprising: measuring the time for erasing said NVRAM array; and comparing said time for erasing with a predetermined maximum erase time, whereby an erase time which exceeds said predetermined maximum erase time indicates a potentially defective NVRAM array.
Claim 7
Independent Claim
51 words
A method for determining the end of useful life for an NVRAM array comprising: measuring the time for erasing said NVRAM array; and comparing said time for erasing with a predetermined maximum erase time, whereby an erase time which exceeds said predetermined maximum erase time indicates a potentially defective NVRAM array.
Claim 8
Dependent Claim
50 words
The method for testing according to claim 5 further comprising: subtracting said time for erasing said NVRAM array from a reference time for erasing said NVRAM array to derive an erase acceleration time; and comparing said erase acceleration time with a stored erase acceleration time to detect a defective array.
Claim 9
Dependent Claim
20 words
The method for testing according to claim 6 further comprising: storing a previously determined erase time as said reference time.
Claim 10
Dependent Claim
34 words
The method for testing according to claim 6 further comprising: storing a subsequently measured erase time as a reference time if said subsequently measured erase time is greater than said previously measured erase time.
Claim 11
Independent Claim
57 words
An apparatus for detecting an end of useful life of an NVRAM array comprising: a counter which times an erase interval for said array; and a comparator for comparing said erase interval with a maximum erase interval, said comparator providing an indication that said NVRAM array is defective when said erase interval exceeds said maximum erase interval.
Claim 12
Independent Claim
57 words
An apparatus for detecting an end of useful life of an NVRAM array comprising: a counter which times an erase interval for said array; and a comparator for comparing said erase interval with a maximum erase interval, said comparator providing an indication that said NVRAM array is defective when said erase interval exceeds said maximum erase interval.
Claim 13
Dependent Claim
55 words
The apparatus according to claim 9 further comprising: a subtractor circuit for measuring the difference between consecutive erase times; and a second comparator for determining whether said difference between said consecutive erase intervals exceeds a maximum erase interval differential, whereby a second indication of the end of useful life of an NVRAM array is produced.
Claim 14
Dependent Claim
53 words
The apparatus according to claim 10 further comprising: a register for storing each measured erase interval produced by said counter, said register providing a previously measured erase interval to a first input of said subtractor circuit and said counter providing a subsequently measured time interval to a second input of said subtractor circuit.
Claim 15
Dependent Claim
48 words
The apparatus for detecting an end for useful life of an NVRAM array according to claim 9 further comprising means for monitoring the threshold voltage of each new cell of an NVRAM array to determine when said array has been erased while said counter times said erase interval.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2004-07-02 | 2005-01-01 | 2005-07-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2008-07-02 | 2009-01-01 | 2009-07-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2012-07-02 | 2013-01-01 | 2013-07-03 | $7700.00 | Window Closed / Lapsed |