Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
2000-09-12
2003-06-03
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S073100, C324S754120
Reexamination Certificate
active
06573699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to devices for measuring electric current waveforms and differential probes, and particularly relates to a device for measuring electric current waveforms and a differential probe wherein the differential probe is designed to measure waveforms of high-speed electric currents flowing through wires by using electro-optical effect.
2. Description of the Related Art
In designing and manufacturing of electrical circuits on printed circuit boards, it is vitally important to measure waveforms of electric currents flowing through wires of the circuits. To this end, various schemes are available for measuring electric currents. A typical method is one that detects an induced magnetic field generated by an electric current.
FIG. 18
is a schematic drawing for explaining a method of current detection by use of an electric probe utilizing a Hall device, which is a typical example of a device that detects an induced magnetic field.
An induced magnetic field that is generated by an electric current flowing through a wire
61
is intensified by a magnetic material ring
62
. The magnetic material ring
62
has a Hall device
63
integrated therein, which works with a detection amplifier
64
to detect the induced magnetic field based on the principle of the Hall effect.
In this case, however, presence of a gap in the magnetic material ring
62
results in a significant decrease in detection sensitivity, so that the magnetic material ring
62
needs to fully circle around the wire
61
. Because of this, the wire
61
that is formed as part of a Cu pattern on a printed circuit board has to be cut, and a lead line has be to be led from the wire
61
.
Since the lead line has its own inductance, the lead line undesirably affects circuit operation if the operation speed is high. This makes it impossible to measure waveforms of high-speed electric currents.
Another method for measuring electric currents is to measure a current from a voltage drop by utilizing the fact that a current flowing through a resistor can be measured from a voltage drop and the resistance. Wires in circuits, however, do not have sufficient resistances to allow a detectable voltage drop to develop. In this case, a resistor needs to be inserted, and a voltage drop between the two end points of the resistor is detected.
When such a voltage drop is measured between the two end points of a resistor device, potentials may be detected at both ends, and a difference between the detected potentials may be obtained thereafter. Such measurement does not provide a true voltage drop waveform in a strict sense since the two measurements are not obtained simultaneously.
For the purpose of measuring an electric current waveform, therefore, a differential probe is often used. In particular, a FET differential probe, which has high input impedance, is useful in measuring high-speed signals.
Electrical differential probes such as FET differential probes, however, are susceptible to error that is caused by asymmetry of circuit structures. Such error may be miniscule, but cannot be ignored since a differential signal to be detected has small amplitudes in comparison with amplitudes of common-mode signals.
Further, since an electrical measurement system is connected to a target system to be measured, the input impedance of a probe decreases in a high-frequency range, affecting the target system to a noticeable degree.
To obviate the problem of input impedance, electro-optical crystal having the Pockels effect may be utilized.
Such electro-optical crystal includes crystal of a vertical type and crystal of a horizontal type. The crystal of a vertical type has a high sensitivity to electric fields that are parallel to the optical axis of passing light, and the crystal of a horizontal type has a high sensitivity to electric fields that are perpendicular to the optical axis. As an example of use of the electro-optical effect of vertical-type electro-optical crystal, a voltage level is measured based on the amount of polarization by detecting the polarization of a laser beam when the laser beam passes through or is reflected by electro-optical crystal in a configuration in which the laser beam is directed to the electro-optical crystal situated in proximity of a measurement point. (See J. A. Valdmanis and G. Mourou, IEEE Journal of Quqntum Electronics, Vol. QE-22, 1986, pp. 69-78.)
FIG. 19
is a schematic diagram for explaining a method of measuring a voltage level by use of a vertical-type electro-optical crystal
71
such as ZnTe, Bi
12
SiO
20
, or the like.
The vertical-type electro-optical crystal
71
has a surface thereof provided with a reflection electrode
72
, on which a probe needle
73
is situated. The other surface of the vertical-type electro-optical crystal
71
has a transparent electrode
74
provided thereon for receiving a reference voltage.
The probe needle
73
comes in contact with a wire
75
formed on a circuit board
76
, so that a target signal
77
is applied to the vertical-type electro-optical crystal
71
via the probe needle
73
. Changes in the applied target signal
77
are detected as the amount of polarization of a laser beam
78
.
This method of measuring a voltage level by use of the vertical-type electro-optical crystal
71
, however, is directed to measurement of a voltage level applied to a wire. Namely, this method cannot be directly applied to measurement of high-speed electric currents that pass through wires in a circuit that is formed on a printed circuit board.
Further, in respect of the vertical-type electro-optical crystal
71
, a travel direction of the laser beam
78
is the same as a direction of a detectable electric field. If the thickness of the vertical-type electro-optical crystal
71
is decreased in order to intensify the electric field, interaction between the laser beam
78
and the vertical-type electro-optical crystal
71
will become weaker. It is thus difficult to step up detection efficiency.
FIG. 20
is a schematic diagram for explaining a method of measuring a voltage level by use of a horizontal-type electro-optical crystal
81
such as LiNbO
3
, LiTaO
3
, or the like. (See Japanese Patent Laid-open Application No. 6-27154.)
In
FIG. 20
, a target voltage E to be measured is applied between nodes a and b of a bridge circuit, and the horizontal-type electro-optical crystal
81
is connected between nodes c and d of the bridge circuit. Light beams from opposite-phase light sources D
1
and D
2
are directed to photosensitive resistors R
1
and R
2
via optical fibers
82
and
83
, respectively. A light beam from a light source D
3
of a measurement unit
86
is directed to and passes through the horizontal-type electro-optical crystal
81
, and the output beam having polarization thereof changed according to the Pockels effect is detected by a photoelectric device PD.
This method of measuring a voltage level is quite peculiar, and merely offers a schematic configuration. In practice, this method cannot be applied to measurement of high-speed electric currents despite the high-impedance feature of the method.
As described above, there is no method to date that measures, with sufficient accuracy by use of a simple configuration, high-speed electric currents as they flow through wires.
Accordingly, there is a need for a scheme that can measure high-speed electric currents with sufficient accuracy by use of a simple configuration.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a device that substantially obviates one or more of the problems caused by the limitations and disadvantages of the related art.
It is another and more specific object of the present invention to provide a device that can measure high-speed electric currents with sufficient accuracy by use of a simple configuration.
In order to achieve the above objects according to the present invention, a device for measuring an electric current of a target circuit includes a pair of contact pins, a r
Fujii Akira
Hama Soichi
Nagai Toshiaki
Sekiguchi Hidenori
Wakana Shin-ichi
Fujitsu Limited
Greer Burns & Crain Ltd.
Nguyen Trung
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