Data processing: measuring – calibrating – or testing – Calibration or correction system
Reexamination Certificate
1999-12-20
2001-03-13
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Calibration or correction system
C702S118000, C702S121000, C324S073100, C714S742000
Reexamination Certificate
active
06202030
ABSTRACT:
BACKGROUND INFORMATION
The invention relates to calibrating test equipment.
Automatic test equipment (ATE) is quite often used to rapidly evaluate the performance of electronic devices (e.g., semiconductor memory devices) to determine if the devices meet predetermined specifications (timing specifications, for example). For example, for each device, the equipment might test the device to obtain a measured specification value (a time, for example) that represents how fast the device performs an operation.
The test equipment may obtain a value that differs from a correct, actual specification value for the device. This difference may be caused by one of many possible sources of variation, such as, for example, variations introduced by test patterns and tester channels that are used to test the device.
Referring to
FIG. 1
, as a result of these variations, the specification values measured by one or more pieces of test equipment may be represented by a Gaussian distribution
10
. Typically, the average value of the distribution
10
is very close to the actual specification value. In light of the distribution
10
, there is a beta risk and an alpha risk for the testing.
Assuming that the measured specification value is determinative of whether the device passes a quality control test, the beta risk represents the probability that a bad device passes the test. As an example, when a minimum response time (a time t
AA
of a memory device, for example) is being measured, the beta risk is the portion of the distribution
10
to the left of the average time. Thus, although the device being tested may have an actual time near the average time, the test results may show the device has a faster time. To minimize the beta risk, a guard band threshold
14
is set to reject all times falling on the side of the threshold
14
that is farthest from the average time.
The alpha risk represents the probability that a good device fails the test. As an example, when a minimum response time of the part (e.g., t
AA
) is being measured, the alpha risk is the portion of the distribution
10
to the right of the average time. Thus, although the device being tested may have an actual time near the average time, the test results may show the device has a slower time.
To test a device, typically different channels of the test equipment are connected to different pins of the device. The test equipment uses the channels to drive some of the pins as inputs and monitor some of the pins as outputs. Each channel typically needs to be routinely calibrated. Otherwise, the measured specification values may vary substantially from the actual specification values.
SUMMARY
The invention is generally directed to using reference electronic devices that have electrical identifications to calibrate at least one channel of test equipment.
In one embodiment, a method includes calibrating uncalibrated test equipment using reference devices. The method includes, for each device, using calibrated test equipment to test the device to obtain a reference specification value. The method also includes selecting one of the devices and retrieving an electrical identification from the selected device. The electrical identification is associated with one of the reference specification values. A channel of the uncalibrated test equipment is used to test the selected device to obtain a measured specification value. The reference specification value that is associated with the electrical identification is compared with the measured specification value, and based on the comparison, the channel is calibrated.
In another embodiment, a system is used with reference devices, and each different reference device has a different electrical identification. The system includes a database and test equipment. The database stores reference specification values. Each reference specification value is associated with a different reference device and is obtained by a test of the device that is performed by calibrated test equipment. The test equipment selects one of the devices, retrieves the electrical identification from the device, and uses the identification to retrieve the reference specification value associated with the selected device. The test equipment also uses a channel of the test equipment to test the selected device to obtain a measured specification value. The test equipment compares the reference specification value (that is associated with the electrical identification) with the measured specification value, and based on this comparison, the test equipment calibrates the channel.
Other advantages and features will become apparent from the following description, from the drawing and from the claims.
REFERENCES:
patent: 4646299 (1987-02-01), Schinabeck et al.
patent: 4928062 (1990-05-01), Miles et al.
patent: 5646521 (1997-07-01), Rosenthal et al.
patent: 5668745 (1997-09-01), Day
patent: 5703489 (1997-12-01), Kuroe
patent: 6032107 (2000-02-01), Hitchcock
Bui Bryan
Hoff Marc S.
Micro)n Technology, Inc.
Trop Pruner & Hu P.C.
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