Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-07-31
2004-01-06
Nguyen, Vinh P. (Department: 2829)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S691000
Reexamination Certificate
active
06674295
ABSTRACT:
BACKGROUND OF THE INVENTION
The priority document for this application, Japanese Patent Application No. 11-221995, is herein incorporated by reference in its entirety, all essential material having been set forth in the specification.
1. Field of the Invention
The present invention relates to an impedance measuring apparatus for an electronic component using a four-terminal method (Kelvin method).
To simplify the description in this specification, an example has been chosen involving the measurement of a resistance to which DC signals are applied. Due to the natures of DC, the only parasitic parameters generated in a circuit are resistance components. When measurement is applied in the case of AC signals, though the parasitic parameters become impedances which are denoted using complex numbers, the concepts are akin to those for the measurement using DC signals.
2. Description of the Related Art
Hitherto, a two-terminal method, as shown in
FIG. 1
, is used to measure the impedance of an electronic component. In this case, a measured value of the impedance can be measured as R
M
=V/I. R
M
, which is measured using this method, includes contact resistances R
H
and R
L
occurring in measurement cables (or terminals), other than the impedance R
dut
of the electronic component, which is a measurement object. This contact resistance includes lead-wire resistances of the measurement cables or the like. R
M
may be expressed as:
R
M
=V/I=R
dut
+R
H
+R
L
When R
H
and R
L
are very high relative to R
dut
, making the value of R
dut
negligible, a measurement error results. The contact resistances R
H
and R
L
vary whenever contact occurs between the measurement object and the measurement terminals. Accordingly, the influence of R
H
and R
L
cannot be removed by means of compensation or the like.
When the measurement error caused by the contact resistances R
H
and R
L
is not negligible, such as a case in which the measurement object has a low impedance, the measurement may be performed using a four-terminal method, as shown in FIG.
2
. In this method, the measured value R
M
=V/I=R
dut
is obtained, and R
H
and R
L
are avoided as measurement error factors.
However, there are problems in the four-terminal method when contact failure occurs at voltage detection lines (H
p
, L
p
). For example, when many measurement objects are measured one after another, the H
p
line is subject to contact failure, as shown in FIG.
3
. If stray capacitance C
HP
is generated on the H
p
line at this time, the stray capacitance appears to have been charged by the voltage obtained on the measurement object before the present measurement of current was obtained. When a measurement object is measured in this state, the following expression is obtained.
R
M
=V
(previous voltage)/
I
(present current)=
R
dut
(1)
The value obtained in this manner is not the resistance of the measurement object currently intended to be measured, as it is influenced by the most recent normal measurement of the measurement object. There is a possibility that measurement failure may occur on the L
p
line as well as the H
p
line, for similar reasons.
Therefore, when a contact failure occurs on a voltage detection line, the measured resistance value is not accurate when a “pure” four-terminal method is used. Because such inaccuracies, there is a risk of delivering defective products instead of good products. In regard to current measurement, when a contact failure occurs at a current-carrying line H
c
or L
c
, measurement cannot be performed since the current I becomes zero.
It is desirable to use a voltage detection unit having a high input impedances R
INH
and R
INL
in the measuring apparatus, yet the input impedances are not infinite. In addition, since the impedance of stray capacitance of the measurement cable is inserted so as to be in parallel, the input impedance is decreased. Accordingly, the voltage detected at the voltage detection unit is voltage-divided by the contact resistances R
HP
and R
LP
, and R
INH
and R
INL
. When R
HP
and R
LP
become too high to be negligible, a measurement error occurs. Since R
HP
and R
LP
vary when contact occurs between the measurement object and the measurement cables, the measurement error due to this cannot be removed by means of a method such as compensation. Furthermore, when measurement using AC signals is performed, there is a possibility that measurement failure may occur because of electrostatic coupling or electromagnetically inductive coupling among the H
c
and L
c
lines, and the H
p
and L
p
lines.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an impedance measuring apparatus for an electronic component in which use of a simple circuit prevents a defective product from being inadvertently determined as a good product when contact failure occurs at a measurement terminal thereof.
It is another object of the present invention to provide an impedance measuring apparatus for an electronic component which decreases the measurement error due to contact resistance.
To this end, according to a first aspect of the present invention, there is provided an impedance measuring apparatus for an electronic component that measures the impedance of the electronic component using a four-terminal method. The impedance measuring apparatus for the electronic component includes a first current-carrying line and a first voltage detection line connected to one electrode of the electronic component; a first resistor establishing a connection between the first current-carrying line and the first voltage detection line; a second current-carrying line and a second voltage detection line connected to the other electrode of the electronic component; and a second resistor establishing a connection between the second current-carrying line and the second voltage detection line. In the impedance measuring apparatus, the first resistor and the second resistor have sufficiently high resistances compared to contact resistances occurring among the electrodes of the electronic component, the current-carrying lines, and the voltage detection lines.
According to a second aspect of the present invention, there is provided an impedance measuring apparatus for an electronic component for measuring the impedance of the electronic component using a four-terminal method. The impedance measuring apparatus for the electronic component includes a first current-carrying line connected to one electrode of the electronic component and a first voltage detection line connected to the other electrode thereof; a first resistor establishing a connection between the first current-carrying line and the first voltage detection line; a second current-carrying line connected to the other electrode of the electronic component and a second voltage detection line connected to the one electrode thereof; and a second resistor establishing the second current-carrying line and the second voltage detection line. In the impedance measuring apparatus, the first resistor and the second resistor have sufficiently high resistances compared to contact resistances occurring among the electrodes of the electronic component, the current-carrying lines, and the voltage detection lines.
The impedance measuring apparatus according to the first aspect of the present invention may be used to effectively determine whether a product is defective or not when the impedance thereof is higher than a standard value. That is, in a measuring apparatus according to the first aspect of the present invention, when the measuring terminals and the electronic component are in good contact with each other, the result is a measurement equivalent to the four-terminal method, and the measured value is the impedance of the electronic component. If any of the measuring terminals fails to be in contact with the electronic component, the result is that the measurement method is converted from the equivalent of a four-terminal method to a two-terminal
Burns Doane , Swecker, Mathis LLP
Murata Manufacturing Co. Ltd.
Nguyen Vinh P.
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