Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1998-11-17
2001-05-22
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
Reexamination Certificate
active
06236220
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to circuit testing and, more particularly, to a method of testing an inductive resonant circuit, especially to the testing of antenna circuits of portable devices, such as contactless chip cards, electronic labels, etc.
BACKGROUND OF THE INVENTION
FIG. 1
is a schematic view of a structure of an integrated circuit
1
working without contact, mounted for example, on a plastic card
20
to form a contactless chip card. This integrated circuit
1
is provided with an antenna circuit
10
comprising a capacitor
11
integrated into the silicon of the integrated circuit
1
and an antenna coil
12
. The antenna coil
12
is mounted on the plastic card
20
and is connected to the terminals of the capacitor
11
by means of connection pads
13
by tin/lead soldering or ultrasonic soldering. The antenna circuit
10
is a resonant circuit whose nominal resonance frequency Fp is generally 13.56 MHz according to prevailing standards. When the antenna coil
12
is placed in an alternating magnetic field Fld locked into the frequency Fp, an alternating voltage Vac appears at its terminals by electromagnetic induction. This alternating voltage Vac could reach 20 to 40 volts under efficient conditions of operation and is converted by a rectifier circuit
14
into a direct voltage Vcc for the integrated circuit.
In general, the antenna coil
12
is not connected to the pads
13
of the integrated circuit
1
except when the integrated circuit
1
is mounted on the plastic card
20
during an advanced stage of manufacturing. The integrated circuit
1
is then covered with a protective resin. At this stage, and despite various controls that may have been planned during the previous steps, occasionally the connection of the antenna coil
12
is faulty, or the integrated capacitor
11
does not have its nominal value. This may be so, for example, because of a drift in the application of the method of manufacture of the integrated circuit. It is therefore desirable to detect these anomalies.
SUMMARY OF THE INVENTION
A object of the present invention is to provide a testing method for determining whether the antenna coil of a contactless chip card, and more generally, a contactless electronic portable device, is defective. More generally, the present invention is aimed at enabling non-visual checking of an inductive resonant circuit. To attain this objective, the present invention relies on the straightforward, but nonetheless, elegant concept of exciting the resonant circuit by inductive coupling and then observing the reaction of the resonant circuit, also by inductive coupling.
More particularly, the present invention provides for a method to test an inductive resonant circuit comprising a capacitor and an antenna coil. The method comprises the steps of exciting the resonant circuit by inductive coupling using a test coil positioned adjacent to the coil of the resonant circuit; sharply interrupting the excitation of the resonant circuit; and then detecting in the test coil a response signal generated by self-induction in the coil of the resonant circuit and retransmitted to the test coil by inductive coupling.
Preferably, the resonant circuit is excited by applying to the test coil a signal at the presumed resonance frequency of the resonant circuit. In practice, the period of excitation of the resonant circuit may be short, and less than one second. If no response signal is detected, the resonant circuit may be considered to be out of operation. If not, the response signal may be analyzed to determine its speed of decrease. When the speed of decrease of the response signal is above a predetermined threshold, the resonant circuit may be considered to be out of operation. Also, the response signal may be analyzed to determine its oscillation frequency. When the oscillation frequency of the response signal is substantially different from the presumed resonance frequency, the resonant circuit may be considered to be out of operation.
REFERENCES:
patent: 3840805 (1974-10-01), Martyashin et al.
patent: 4392106 (1983-07-01), Yakovlev et al.
patent: 4973912 (1990-11-01), Kaminski et al.
patent: 5631572 (1997-05-01), Sheen et al.
patent: 5898298 (1999-04-01), Brandsma et al.
Patent Abstracts of Japan, vol. 018, No. 272, May 24, 1994 and JP 06 047513 A (Sumitomo Light Metal Ind. Ltd.), Feb. 22, 1994.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Galanthay Theodore E.
Kerveros J
Metjahic Safet
STMicroelectronics S.A.
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