Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1998-10-27
2002-03-26
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S661000, C324S671000, C341S033000
Reexamination Certificate
active
06362633
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a capacitive distance sensor, in particular, a small-distance (micrometric to millimetric) sensor.
Small-distance sensors are used, among other things, as pressure, proximity, roughness, mechanical stress and acceleration sensors, for example, in integrated microphony and for acquiring fingerprints.
For fingerprint acquisition in particular (to which reference is made herein purely by way of example of a preferred application of the present invention), known sensors include various types, for example: optical, piezoelectric, variable-conductance, thermal, ultrasonic and capacitive, the most promising of which in terms of precision, size, production and cost are capacitive sensors.
Capacitive sensors are based on the principle that the capacitance between two plates is inversely proportional to the distance between them, so that, using the contacting dermal tissue itself as the second plate of the sensor capacitor, and by determining the capacitance, it is possible to locate the ridges and grooves of the fingerprint. This is the principle used in U.S. Pat. No. 5,325,442 to Knapp, which relates to a sensor comprising an array of elementary cells, each comprising a sensitive electrode and an electronic switching device. The electrode is coated with dielectric material, such as passivation oxide or a polymer compound, onto which the epidermis is placed. When a cell is selected, a predetermined variation in potential is applied to the electrode to induce at the terminals an appropriate variation in charge. The extent of variation in charge depends on the capacitance associated with the electrode and is read by amplifying elements connected to the output of the device. To improve efficiency, the above patent suggests a surface grid connected to a reference potential to appropriately bias the skin tissue.
In the above known capacitive sensor, the capacitance between the plates of a capacitor varies in inverse proportion to the distance between the plates, which therefore poses the problem of normalizing the resulting data. In particular, if the capacitance being measured is very small, as in the application in question, serious difficulty is encountered in detecting the charge and discriminating between the various intermediate charge levels corresponding to different grey levels of the image to be generated in the presence of a low signal
oise ratio.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a sensor designed to overcome the drawbacks typically associated with known technology.
A preferred embodiment of the present invention is directed to a capacitive distance sensor for measuring small distances. The distance sensor includes a capacitive element having a first plate positioned facing a second plate. The first and second plates define a distance to be measured. The distance sensor also includes an amplifying means defining an input and an output. The capacitive element is connected between the input and the output to form a negative feedback branch.
In practice, according to the present invention, the detecting capacitor, the distance between the plates of which is to be determined, is placed in a negative feedback loop, thus inverting between the denominator and the numerator the dependance of the output voltage on the distance between the plates.
REFERENCES:
patent: 3493855 (1970-02-01), Norwich
patent: 3641431 (1972-02-01), Pigage et al.
patent: 3781855 (1973-12-01), Killen
patent: 3873927 (1975-03-01), Overall
patent: 3967310 (1976-06-01), Horiuchi et al.
patent: 4016490 (1977-04-01), Weckenmann et al.
patent: 4096758 (1978-06-01), Moore
patent: 4161743 (1979-07-01), Yonezawa et al.
patent: 4183060 (1980-01-01), Barnette et al.
patent: 4353056 (1982-10-01), Tsikos
patent: 4394773 (1983-07-01), Ruell
patent: 4428670 (1984-01-01), Ruell et al.
patent: 4429413 (1984-01-01), Edwards
patent: 4513298 (1985-04-01), Scheu
patent: 4571543 (1986-02-01), Raymond et al.
patent: 4577345 (1986-03-01), Abramov
patent: 4626774 (1986-12-01), Regtien
patent: 4656871 (1987-04-01), Czarnocki
patent: 4763063 (1988-08-01), Shkedi
patent: 4814691 (1989-03-01), Garbini et al.
patent: 4935207 (1990-06-01), Stanbro et al.
patent: 4958129 (1990-09-01), Poduje et al.
patent: 5028876 (1991-07-01), Cadwell
patent: 5325442 (1994-06-01), Knapp
patent: 5373181 (1994-12-01), Scheiter et al.
patent: 5430381 (1995-07-01), Dower
patent: 5467022 (1995-11-01), Aoki et al.
patent: 5530581 (1996-06-01), Cogan
patent: 5659626 (1997-08-01), Ort et al.
patent: 5778089 (1998-07-01), Borza
patent: 5828773 (1998-10-01), Setlak et al.
patent: 5844415 (1998-12-01), Gershenfeld et al.
patent: 5852670 (1998-12-01), Setlak et al.
patent: 5862248 (1999-01-01), Salatino et al.
patent: 5869791 (1999-02-01), Young
patent: 5903225 (1999-05-01), Schmitt et al.
patent: 5920640 (1999-07-01), Salatino et al.
patent: 5963412 (1999-08-01), Gershenfeld et al.
patent: 5973623 (1999-10-01), Gupta et al.
patent: 6011859 (2000-01-01), Kalnitsky et al.
patent: 6025726 (2000-02-01), Gershenfeld et al.
patent: 6051981 (2000-04-01), Gershenfeld
patent: 6066954 (2000-05-01), Gershenfeld et al.
patent: 6114862 (2000-09-01), Tartagni et al.
patent: 0 226 082 (1987-06-01), None
patent: 0 397 244 (1990-11-01), None
patent: 0 397 244 (1990-11-01), None
patent: 0 397 244 (1990-11-01), None
patent: 0 454 883 (1991-06-01), None
patent: 0 455 070 (1991-06-01), None
patent: 0 710 593 (1996-05-01), None
patent: 0 779 497 (1997-06-01), None
patent: 0 779 497 (1997-06-01), None
patent: 0 786 745 (1997-07-01), None
patent: 0 786 745 (1997-07-01), None
patent: 0 790 479 (1997-08-01), None
patent: 0 791 899 (1997-08-01), None
patent: 0 791 899 (1997-08-01), None
patent: 2279756 (1995-01-01), None
patent: 2279757 (1995-01-01), None
patent: 2312514 (1997-10-01), None
patent: WO 97/40744 (1997-11-01), None
patent: WO 98/49691 (1998-11-01), None
patent: WO 99/28701 (1999-06-01), None
Young et al., “Novel Fingerprint Scanning Arrays Using Polysilicon TFT's on Glass and Polymer Substrates,”IEEE Electron Device Letters,8(1):19-20, 1997, (Month Unavailable).
Tartagni et al., “A 390dpi Live Fingerprint Imager Based on Feedback Capacitive Sensing Scheme,” IEEE International Solid-State Circuits Conference, Feb. 7, 1997, 5 pp.
Sarma and Barranger, “Capacitance-Type Blade-Tip Clearance Measurement System Using a Dual Amplifier with Ramp/DC Inputs and Integration,”IEEE 41(5):674-678, Oct. 1992.
Woffenbuttel and Regtien, “Integrated Tactile Imager With an Intrinsic Contour Detection Option,”Sensors and Actuators 16:141-153, 1989 (Month Unavailable).
Carlson David V.
Horgenson Lisa K.
Metjahic Safet
Nguyen Vincent Q.
SEED IP Law Group PLLC
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