Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1998-12-10
2001-07-03
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB, C324S763010, C340S146200
Reexamination Certificate
active
06255839
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an IC testing apparatus (commonly called IC tester) for testing a semiconductor integrated circuit (hereinafter referred to as IC), and more particularly, to a voltage applied type current measuring circuit utilized in testing a logic IC formed by, for example, a CMOS or CMOSs (Complementary Metal Oxide Semiconductor or Semiconductors) to determine whether a leakage current flows or not through input terminal pins of the logic IC (hereinafter referred to as CMOS.IC). Herein, the voltage applied type current measuring circuit means a circuit for applying a voltage to an IC under test and measuring a current flow through the IC.
2. Description of the Related Art
In an IC tester, a function test for applying a varying voltage to an IC under test (commonly called DUT) and measuring in what manner the output of the IC under test is varied can be performed at high speed for each input terminal pin of the IC under test.
A feature of the CMOS.IC which is one of various types of ICs is such that its input current is small or zero, but a circuit for measuring a minute or micro current is needed to test such CMOS.IC. However, such micro current measuring circuit is usually slow in response, and hence it is customary in the prior art that the measurement of current through a CMOS.IC is conducted separately of the function test thereof.
FIG. 3
shows an example of an associated circuit part of a conventional IC tester having a voltage applied type current measuring circuit for measuring a minute or micro current through an IC under test.
There are provided, for each of pins of an IC under test (DUT)
11
, a plurality of input/output blocks
12
-
1
,
12
-
2
, . . . ,
12
-n (n being an integer equal to the number of the pins of the IC under test and equal to or greater than one). Each input/output block (I/O block) comprises a driver
13
for applying a predetermined voltage to corresponding one of the pins of the IC under test
11
, a comparator
16
for comparing an output voltage from the IC under test
11
with a reference voltage, and a voltage applied type current measuring circuit
17
.
The output terminal of the driver
13
is connected to an input/output terminal
15
of that I/O block via a first switch
14
, and the connection point (junction) of the output terminal of the driver
13
and the first switch
14
is connected to an input terminal of the comparator
16
.
The voltage applied type current measuring circuit
17
comprises a digital-to-analog converter (D/A converter)
18
, a buffer circuit
19
having its non-inverting input terminal connected to the output terminal of the D/A converter
18
, a differential amplifier
23
having its inverting input terminal connected to the output terminal of the buffer circuit
19
and its non-inverting terminal connected to the output terminal of the D/A converter
18
, and a current detecting resistance element
21
the input side of which is connected to the output terminal of the buffer circuit
19
and the output side of which is connected to the inverting input terminal of the buffer circuit
19
and one end of a second switch
22
. Accordingly, the output terminal of the buffer circuit
19
is connected to the input/output terminal
15
of that I/O block via the current detecting resistance element
21
and the second switch
22
in series.
The output terminal of the differential amplifier
23
in each I/O block
12
-i (i=1, 2, . . . , n) is connected to an analog-to-digital converter (AD converter)
25
via a switch
24
-i (i=1, 2, . . . , n) provided in each of the I/O blocks. Further, an operating power supply
26
is connected to a power supply terminal pin of the IC under test
11
.
In case of measuring a current flow through an IC under test under a predetermined voltage applied thereto, namely, in case of the voltage applied type current measurement, each of the input/output terminals of the I/O blocks
12
-
1
to
12
-n is connected to corresponding one of the pins of the IC under test
11
, a digital value set in correspondence to a testing voltage is inputted into the D/A converter
18
under the condition that the first switch
14
and the second switch
22
in each I/O block are turned off and on respectively, and then a testing voltage outputted from the D/A converter
18
is applied to each of the pins of the IC under test
11
.
By this procedure, a voltage developed across the current detecting resistance element
21
in correspondence to a current flow through each pin of the IC under test
11
can be detected by the differential amplifier
23
constructed as stated below, and therefore, by sequentially turning on the switches
24
-
1
to
24
-n one after another, a voltage corresponding to an input current flow into each I/O block which has been turned on, that is, to an input current flow into each pin of the IC under test
11
connected to that I/O block which has been turned on can be obtained from the A/D converter
25
as digital data.
The differential amplifier
23
actually has such a circuit construction, as shown in
FIG. 4
, that the inverting input terminal
27
thereof is connected to a non-inverting input terminal of a buffer
28
, an output terminal of the buffer
28
is connected to an inverting input terminal thereof as well as to an inverting input terminal of a differential amplifier
31
via a first resistance element
29
(R
1
), a second resistance element
35
(R
2
) is connected between an inverting input terminal and an output terminal of the differential amplifier
31
, the non-inverting input terminal
32
of the differential amplifier
23
is connected to a non-inverting input terminal of the differential amplifier
31
via a third resistance element
33
(R
3
), this non-inverting input terminal of the differential amplifier
31
is connected to the ground via a fourth resistance element
34
(R
4
), and an output element of the differential amplifier
31
is connected to the output terminal
36
of the differential amplifier
23
. Accordingly, to the output terminal
36
of the differential amplifier
23
is outputted a difference voltage V
C
between the voltage V
A
at the inverting input terminal
27
and the voltage V
B
at the non-inverting input terminal
32
, and a voltage corresponding to an input current flow into each pin of the IC under test
11
can be obtained from the A/D converter
25
as digital data.
The differential amplifier
23
must be designed by taking into consideration a common-mode rejection ratio (CMRR), that is, a characteristic of rate or ratio where signals inputted into the two input terminals
27
and
32
in phase with each other are rejected. If this common-mode rejection ratio is inappropriate, it is difficult to measure an input current with high accuracy. The common-mode rejection ratio is affected by errors in the resistance values of the resistance elements
29
,
33
,
34
and
35
.
Letting the resistance values of the resistance elements
29
,
35
,
33
and
34
be represented by R
1
, R
2
, R
3
and R
4
, respectively, and assuming that the resistance value of each of the resistance elements has an error &agr;, the relationship between voltage V
A
at the inverting input terminal
27
, voltage V
B
at the non-inverting input terminal
32
, and voltage V
C
at the output terminal
36
can be expressed by the following equation.
V
C
=
V
A
·
R2
R1
-
V
B
·
R4
R3
+
R4
·
R1
+
R2
R1
Therefore, putting R
1
=R(1±&agr;), R
2
=R(1∓&agr;), R
3
=R(1∓&agr;), R
4
=R(1±&agr;), V
A
=V
B
, then V
C
=4&agr;. For example, assuming that V
B
=5 V and &agr;=0.1%, the error is 50×0.1%×4=20 mV at the maximum.
Since such a large error occurs, the minute current measurement requires to use the resistance elements
29
,
33
,
34
and
35
having extremely high-precision resistance values, respectively, which are very expensive resista
Advantest Corporation
Gallagher & Lathrop
Lathrop David N.
Metjahic Safet
Nguyen Jimmy
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