Electricity: measuring and testing – Electrostatic field
Reexamination Certificate
2001-01-04
2002-12-24
Oda, Christine K. (Department: 2858)
Electricity: measuring and testing
Electrostatic field
C324S072000
Reexamination Certificate
active
06498493
ABSTRACT:
This patent application claims priority based on Japanese patent application, 2000-1998 filed on Jan. 7th, 2000.
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an electric potential detector, a device tester, and a method of detecting electric potential.
2. Description of Related Art
A device tester has to accurately measure a voltage output from a device to secure a reliability of the testing. Moreover, an electric current that flows into the device and the electric current that flows out of the device also have to be measured accurately.
FIG. 1
shows a conventional electric potential detector. The electric potential V that is input from an input terminal
30
is input to both an A/D convertor
810
and analog comparators
820
and
830
. Each of the A/D convertor
810
and the comparators
820
and
830
are comprised for performing a determination of the digital value of the electric potential V and a judgement (pass/fail judgement) of whether the electric potential V exists within an allowable range. The pass/fail judgement can be known by comparing the maximum and minimum value of the allowable range and the value of the electric potential V.
Details of the pass/fail judgement will be explained. A maximum value of an allowable range of an electric potential is provided to the plus side of an input terminal of the comparator
820
from the D/A convertor
840
, and a comparison is performed between the maximum value and an analog value of the electric potential V, which is input to a minus side of an input terminal. When the analog value of the electric potential V is larger than the maximum value, the comparator
820
sets the logic of the HFAIL signal as L level and informs that the electric potential V is “HIGH FAIL”. On the other hand, when the analog value of the electric potential V is smaller than the maximum value, the comparator
820
outputs a signal of H level as an HFAIL signal and informs that the electric potential V is “HIGH PASS”.
Similarly, a minimum value is input to a minus side of an input terminal of the comparator
830
from a D/A convertor
850
, and the electric potential V is input to a plus side of an input terminal. The comparator
830
sets the logic of the LFAIL signal to be L level (LOW FAIL) or H level (LOW PASS) according to the comparison result.
In the configuration of
FIG. 1
, the determination of the digital value (A/D conversion) is performed at the A/D convertor
810
, and the pass/fail judgement is performed at the comparator
820
and
830
, independently. It cannot be avoided that a few differences arise among the characteristics of the A/D convertor
810
and the comparator
820
and
830
during the manufacturing process. Therefore, there is a problem that inconsistency of the result arises such that the judgement is a fail although the digital value is within the allowable range. To solve the above mentioned problems, an electric potential detector shown in
FIG. 2
was used.
FIG. 2
is a circuit diagram that shows another configuration of the conventional electric potential detector. First, the analog electric potential V input from the input terminal
30
is converted to digital by the A/D convertor
810
. The digital value of the electric potential V output from the A/D convertor
810
is then input to both of the digital comparator
920
and
930
. Each of the maximum value and the minimum value are further input to the comparator
920
and
930
, respectively, from the limit resistor
940
and
950
, and the pass/fail judgement is performed as in the same way as in the configuration of FIG.
1
.
As is clear from the above explanation, the pass/fail judgement is performed for the output of the A/D convertor
810
in the configuration of FIG.
2
. Thus, the inconsistency of the result as in the case of
FIG. 1
does not arise. However, the electric potential V has to be A/D converted even when it is sufficient to perform only the pass/fail judgement so that it takes a long time for a judgement.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an electric potential detector, device tester, and a method of detecting electric potential that has a configuration of performing a judgement at high speed without causing an inconsistency of testing results in view of the above issues. This object is achieved by combinations of characteristics described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
To solve the above problems, the first aspect of the present embodiment is characterized in that the first embodiment comprises a comparator that compares an input electric potential, which is an object to be detected, with a referential value and outputs a comparison result; and a control circuit that has: a judgement means for performing a judgement of pass/fail of the input electric potential based on the comparison result obtained by providing an allowable limit value, which is a value indicating an allowable limit of an input electric potential, as the referential value; and a value determination means for finding a value of the input electric potential based on the comparison result obtained by providing the referential value to the comparator by varying the referential value.
The second aspect of the present invention is characterized in that the control circuit provides the comparator with a maximum value and a minimum value of an allowable range of the input electric potential, which is the allowable limit value, as the referential value and judges that the input electric potential is a failure when the input electric potential is judged as higher than the maximum value or judged as lower than the minimum value by the comparator.
The third aspect of the present invention is characterized in that the value determination means detects a transition point of the comparison result by selecting a value from a plurality of candidate values one after another arbitrarily as the referential value and determines a value of the input electric potential based on a candidate value that corresponds to the transition point.
The fourth aspect of the present invention is characterized in that the comparator includes a first and a second comparator to which the maximum value and the minimum value are input respectively; and the control circuit judges whether the input electric potential is allowable at a high potential side based on a comparison result of the first comparator and judges whether the input electric potential is allowable at a low potential side based on a comparison result of the second comparator.
The fifth aspect of the present invention characterized in that the input electric potential is analog; and the judging means provides the maximum value and the minimum value to the comparator at different timings; and the electric potential detector further comprises: a retaining means that retains the input electric potential while the maximum value and the minimum value are provided to the comparator.
The sixth aspect of the present invention is characterized in that the electric potential detector further comprises: an input electric potential retaining means for retaining the input electric potential during selection of a value from the plurality of candidate values one after another arbitrarily as the referential value.
The seventh aspect of the present invention is a device tester that comprises: a test pattern generator that generates an input test pattern, which is to be input to a device under test (DUT), and an expectation pattern, which is to be output from the DUT into which the input test pattern is input; a device testing comparator for judging a propriety of the DUT according to whether an output pattern, which is output from the DUT according to the input test pattern that is input to the DUT, and the expectation pattern matches; a power supply for supplying electric power to the DUT; and a terminal potential detecting circuit for detecting an electric potential of a terminal
Advantest Corporation
Oda Christine K.
Rosenthal & Osha L.L.P.
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