Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-07-20
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
C324S763010, C323S316000
Reexamination Certificate
active
06255842
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an applied-voltage-based current measuring device that can be used, for example, to make a check to determine whether the DC characteristic of each terminal of a semiconductor integrated circuit element (hereinafter referred to as an IC) falls within a predetermined range.
BACKGROUND ART
IC tests fall into a function test and a DC test. The function test is a test to see if the IC under test performs predetermined functions. The DC test is a test to see if a leakage current at an input terminal of the IC under test, for instance, is smaller than a predetermined value, or if the output current at an output terminal is larger than a predetermined value.
The present invention is directed to improvements in an applied-voltage-based current measuring device for use in the DC test; in particular, the invention is to adapt the current measuring device to be capable of measuring current values accurately without using any highly precision resistors and at high speed without switching between current measuring ranges.
In
FIG. 4
there is depicted an example of a conventional applied-voltage-based current measuring device. In
FIG. 4
, reference numeral
11
denotes an IC under test,
12
a voltage source from which a predetermined voltage is applied to a terminal of the IC under test, and
13
current measuring means for measuring current that flows to the terminal of the IC under test
11
during periods of voltage application. The applied-voltage-based current measuring device is composed of the voltage source
12
and the current measuring means
13
.
The voltage source
12
is made up of an operational amplifier
12
A and a D/A converter
12
B which supplies a voltage equal to a voltage to be applied to a terminal of the IC under test
11
. To an inverting input terminal of the operational amplifier
12
A is fed back from a sensing point (a voltage sensing point) SEN a voltage V
1
applied to the terminal of the IC under test
11
; by this feedback operation, the voltage V
1
is made to match a voltage V
DA
from the D/A converter
12
B, thus applying an intended voltage (for example, a voltage that defines H logic and L logic) to the terminal of the IC under test
11
.
The current measuring means
13
is made up of a current measuring resistor R
1
connected between an output terminal of the operational amplifier
12
A and the sensing point SEN, a subtractor circuit
13
A for extracting a voltage that develops across the current measuring resistor R
1
, and an A/D converter
13
B for A/D conversion of the voltage extracted by the subtractor circuit
13
A.
Incidentally, reference characters R
2
and R
3
denote resistors for range changeover use. These range change-over resistors R
2
and R
3
are adapted to be connected in parallel to the current measuring resistor R
1
through selective turning-ON of range change-over switches S
2
and S
3
, thereby switching the current measuring means
13
between its current measuring ranges.
That is, when the range change-over switches S
2
and S
3
are both in the OFF state and when the range change-over switch S
2
is in the ON state, the current measuring means is put in the state of measuring a leakage current at one of terminals of the IC under test which is held in the input mode, and it measures minute currents approximately in the range of several to tens of microamperes. To perform this, the resistance values of the current measuring resistors R
1
and R
2
are chosen relatively large on the order of tens of kiloohms.
On the other hand, the resistance value of the range switch-over resistor R
3
is chosen relatively small, for example, 10 ohms or so. Accordingly, when the switch S
3
is put in the ON state, the current measuring means is switched to a measuring range of a relatively large current value, and measures current is provided from that one of terminals of the IC under test
11
which is held in the output mode.
The circuit configuration of
FIG. 4
has the defect of requiring the range change-over switches S
2
and S
3
. In other words, since the range change-over switches S
2
and S
3
are connected in series to the circuit through which the current to be measured flows, it is necessary, in particular, to minimize the ON-state resistance of the range change-over switch S
3
through which a large current flows. On this account, a CMOS-structured semiconductor switching element cannot be used as the range change-over switch S
3
, but instead a relay is used commonly. Because of the relay's slow response, much time is needed for switching the measuring range. Furthermore, the current measurement starts at a high-sensitivity measuring range, and when the measured value falls outside it, the measuring range is switched to the next one and the current measurement is carried out again. This inevitably provides disadvantages that the switching of the measuring range is time-consuming and that when the measuring range is switched from a minute to a large current one (by turning ON the switch S
3
), much time is also taken for the circuit to settle back after the switching of the measuring range. The prior art example has another disadvantage of requiring much time for test because of repeating for each terminal the measurements of a leakage current and the output current of the IC under test
11
through the use of a single applied-voltage-based current measuring device.
Besides, the subtractor circuit
13
A comprises, as depicted in
FIG. 4
, an operational amplifier A
1
, a buffer amplifier A
2
and resistors R
11
, R
12
, R
13
and R
14
. In this arrangement the resistance values of the resistors R
11
, R
12
, R
13
and R
14
need to be set, for example, such that R
12
/R
11
=R
14
/R
13
=1. This relationship of the resistors R
11
to R
14
has a significant effect on the determination of the gain of the operational amplifier A
1
and the determination of its common-mode rejection ratio. Since the resistance values of the resistors R
11
and R
12
to R
14
must therefore be set with high accuracy, the manufacturing cost of the subtractor circuit
13
A is high, in particular, when implemented in an IC, because of difficulty in setting the resistance values of the resistors R
11
to R
14
with high accuracy.
As a solution to the above problems, there has been proposed such a circuit as shown in FIG.
5
. In this circuit a series circuit of the range change-over resistor R
2
and the range change-over switch S
2
and diodes D
1
and D
2
are connected in parallel to the current measuring resistor R
1
, and the resistor R
3
for large current measuring use is independently connected in series to the current measuring resistor R
1
; voltages that develop across the resistors R
1
and R
3
are extracted by subtractor circuits
13
A and
13
A′, and the voltages thus extracted by the subtractor circuits
13
A and
13
A′ are selectively provided via switches S
22
and S
33
into the A/D converter
13
B.
With this circuit configuration, in a minute current region (a current region in which the diodes D
1
and D
2
remain OFF) the switch S
22
is held in the ON state, through which a voltage developed by a current flow through the current measuring resistor R
1
or a parallel circuit of the resistors R
1
and R
2
is applied to the A/D converter
13
B to measure a minute current (a leakage current at each terminal of the IC under test
11
).
In a large current region, since the voltage across the current measuring resistor R
1
exceeds a value at which the diode D
1
or D
2
turns ON, a large current bypasses R
1
through the diode D
1
or D
2
and the voltage across the current measuring resistor R
1
is clamped at a conduction voltage (for example, 0.6 V or so) of the diode D
1
or D
2
; in this state, a voltage across the current measuring resistor R
3
is extracted by the subtractor circuit
13
A′ and provided via the switch S
23
to the A/D converter
13
B for measuring the large current.
With the circuit configuration depicted in
FIG. 5
, i
Advantest Corporation
Gallagher & Lathrop
Kerveros J.
Lathrop David N.
Metjahic Safet
LandOfFree
Applied-voltage-based current measuring method and device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Applied-voltage-based current measuring method and device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Applied-voltage-based current measuring method and device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2501617