(12) United States Patent
`Gu ta et al.
`
`(10) Patent N0.:
`45 Date of Patent:
`
`US 6,225,711 B1
`*Ma 1 2001
`a
`
`US006225711B1
`
`(54) SOLID STATE CAPACITIVE SWITCH
`
`Alan Henry
`Inventors: Bhusan Gupta, Palo
`Kramer, Berkeley, both of CA (US)
`
`8/1998 Smigelski ............................ .. 341/33
`5,796,355
`2/1999 Caldwell
`341/33
`5,867,111
`5,933,102 * 8/1999 Miller 6[ 8.1. ......................... .. 341/33
`* Cited by examiner
`
`_
`(*) Notice:
`
`Jackson
`Primary Examiner_stephen
`Assistant Examiner—Robert L. Deberadinis
`(74) Attorney, Agent, or Firm—Theodore E. Galanthay;
`Lisa K jorgenson; Bryan A_ Santarem
`
`Assignee: STMicroelectronics, IIlC-, Carrollton,
`TX (Us)
`_
`_
`_
`This‘ patent issued on a continued pros-
`ecutlon appllcatlon ?led under 37 CFR
`ABSTRACT
`(57)
`1.53(d), and is subject to the twenty year
`ligtzarm provlslons of 35 USC' A ?ngertip-operated solid state capacitance switch detects a
`'
`capacity change that is induced by the physical contact of an
`Subject to any disclaimer the term of this
`ungrounded ?ngertip to an external dielectric surface of the
`patent is extended or adjusted under 35
`solid state sWitch. The input and output of a solid state
`U S C 154(k)) by 0 days
`signal-inverting ampli?er are respectively connected to tWo
`'
`'
`'
`'
`relatively large and ungrounded capacitor plates that are
`associated With, but electrically isolated from, the sWitch’s
`external dielectric surface. An ungrounded ?ngertip forms a
`third capacitor plate on the sWitch’s external surface. The
`solid state ampli?er detects the presence of a ?ngertip on the
`sWitch’s external surface by Way of a change in capacitance
`Within a compound, three plate, capacitor that includes the
`tWo ungrounded capacitor plates and the ungrounded ?n
`gertip that is resident on the sWitch’s external surface. An
`automatic gain control circuit is provided to adjust the value
`of an ampli?er reference voltage When the solid state sWitch
`is not operating, thereby alloWing the solid state sWitch to
`adapt to changeable ambient conditions. A momentary
`sWitch and a toggle ?ip-?op latched sWitch are provided. A
`linear sWitch array having a movable control knob and a
`linear LED indicator array is provided. The momentary solid
`state sWitch is constructed to operate as a temporal code
`detector that detects a coded sequence of sWitch-taps and a
`coded time interval betWeen adjacent sWitch-taps.
`
`_
`(21) Appl' NO" 09/374’716
`(22) Filed;
`Aug, 13, 1999
`
`Related US. Application Data
`
`(62) Division of application No. 08/957,972, ?led on Oct. 21,
`1997: HOW Pat NO- 5973:623-
`(51) Int (17 __
`_______________________ __ H01H 35/00
`(52) us CL ________________ __
`307/125. ZOO/343. 341/33
`(58) Field of Search
`’
`203 B1B 512
`341/573 1 554 4’
`’
`’
`’
`562: 3’ 61/131’
`’
`
`(56)
`
`References Cited
`
`4 353 056
`4,939,382
`5,325,442
`
`U.S. PATENT DOCUMENTS
`340/146 3
`10/1982 Tsikos
`307/116
`7/1990 Graoudis
`6/1994 Knapp .................................... .. 382/4
`
`11 Claims, 8 Drawing Sheets
`
`_ _ _ — _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.._...l____________.__._._.__._____._.__._
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`Neodron Ltd.
`Exhibit 2007
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`U.S. Patent
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`May 1, 2001
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`Sheet 1 of8
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`US 6,225,711 B1
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`FROM
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`VERTICAL SCAN
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`U.S. Patent
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`US 6,225,711 B1
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`U.S. Patent
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`May1, 2001
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`Sheet 3 of 8
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`US 6,225,711 B1
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`U.S. Patent
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`May 1, 2001
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`Sheet 4 of 8
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`US 6,225,711 B1
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`U.S. Patent
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`May 1, 2001
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`Sheet 5 of 8
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`US 6,225,711 B1
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`U.S. Patent
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`May1, 2001
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`Sheet 6 of 8
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`U.S. Patent
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`May 1, 2001
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`Sheet 7 of 8
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`US 6,225,711 B1
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`U.S. Patent
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`May 1, 2001
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`Sheet 8 of 8
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`US 6,225,711 B1
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`US 6,225,711 B1
`
`1
`SOLID STATE CAPACITIVE SWITCH
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application is a Divisional of pending US. patent
`application Ser. No. 08/957,972, ?led Oct. 21, 1997, now
`US. Pat. No. 5,973,623.
`
`BACKGROUND OF THE INVENTION
`
`2
`contains an article entitled NOVEL FINGERPRINT SCAN -
`NING ARRAYS USING POLYSILICON TFT’S OF
`GLASS AND POLYMER SUBSTRATES. This article
`describes a tWo-dimensional (2-D), 200><200, capacitance
`sensing array that is made up of 40,000 individual pixels.
`Each pixel of the array includes tWo Thin Film Transistors
`(TFTs) and a capacitor plate. Each array pixel resides at the
`intersection of an array-roW and an array-column, and each
`array pixel is individually addressable by Way of roW-driver
`circuits and column-driver circuits.
`Considering the tWo TFTs, hereinafter called TFT-A and
`TFT-B, that are associated With a given pixel, the drain
`electrodes of TFT-A and TFT-B are connected to the pixel’s
`capacitor plate, the gate electrode and the source electrode
`of TFT-A are connected to a roW-conductor that is associated
`With the pixel, the gate of TFT-B is connected to the
`folloWing roW-conductor, and the source of TFT-B is con
`nected to a column-conductor that is associated With the
`pixel.
`A thin (0.1 micrometer) silicon nitride insulator overlies
`the capacitor plate of each array pixel. When the ridge of a
`?ngerprint lies directly over the capacitor plate, a capacitor
`is formed betWeen the capacitor plate and the ?nger. This
`capacitor is charged When a roW-pulse (8 to 10 VDC, and of
`10 to 100 micro second duration) is applied to the pixel by
`Way of the roW-conductor that is associated With this pixel
`and TFT-A. This stored charge is thereafter transferred onto
`the pixel’s column-conductor through TFT-B When a roW
`pulse is applied to the folloWing roW-electrode.
`Also of interest is the publication 1997 IEEE INTERNA
`TIONAL SOLID-STATE CIRCUITS CONFERENCE that
`contains and article beginning page 200 entitled A 390DPI
`LIVE FINGERPRINT IMAGER BASED ON FEEDBACK
`CAPACITIVE SENSING SCHEME. This article describes
`a single-chip, 200><200 element array, 2-metal digital CMOS
`technology, sensor that is based upon feedback capacitance
`sensing, and that operates to detect the electrical ?eld
`variation that is induced by the ?nger’s skin surface. In each
`element of the array, tWo horiZontally spaced metal plates
`are separated from the overlying and adjacent portion of the
`?nger’s skin surface by passivation oxide. Since the distance
`betWeen the skin and the sensor’s surface identi?es the
`presence of the ?ngerprint’s ridges and valleys, an array of
`elements provides a complete ?ngerprint pattern.
`In each element of the array, the tWo metal plates are
`respectively connected to the input and the output of a
`high-gain inverter, to thereby form a charge-integrator. In
`operation, the charge-integrator is ?rst reset by shorting the
`input and output of the inverter. A?xed amount of charge is
`then sinked from the input, causing the output voltage to
`sWing inversely proportional to a feedback capacitance
`value that is inversely proportional to the distance to the
`?ngerprint’s ridges and valleys. The array of cells, or
`sensors, thus provides the complete ?ngerprint pattern. The
`?ngerprint image disappears When the ?nger is removed
`from the array.
`US. Pat. No. 4,353,056, incorporated herein by reference,
`is of interest in that it relates to a capacitance type ?ngerprint
`sensor Wherein a ?nger is pressed onto the sensor’s surface
`in order to read the ridges and valleys of the ?ngerprint. The
`sensor-surface has a large number of capacitors of a small
`physical siZe associated thereWith. TWo sensors are
`described. In a ?rst type of sensor, an electrical insulator
`carries a number of ?exible and horiZontally spaced curved
`metal electrodes, tWo adjacent metal electrodes of Which
`comprise one capacitor. Aprotective insulating ?lm overlies
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`1. Field of the Invention
`This invention relates to the ?eld of electrical circuit
`switching, and more speci?cally, this invention relates to an
`object-operable, single pixel, capacitance type, solid state
`sWitch.
`2. Description of the Related Art
`US. patent application Ser. No. 08/799,548 by Marco
`Tartagni, ?led Feb. 13, 1997, and entitled CAPACITIVE
`DISTANCE SENSOR is incorporated herein by reference.
`This application describes an Integrated Circuit (IC) capaci
`tive distance sensor having a number of uses, including
`?ngerprint acquisition. In this IC device, a portion of Which
`is shoWn in FIGS. 1—3 of the present application, each
`individual cell 2 of a multi-cell array 3 includes a pair of ?at
`armatures 23,24 that are spaced from each other in a
`horiZontal plane to form a capacitor and to de?ne a vertical
`distance “d” to be measured. Each cell 2 also includes the
`FIG. 2 ampli?er arrangement Whose input 16 is connected to
`one armature 24, and Whose output 17 is connected to the
`other armature 23, such that the armature/capacitor com
`prises an ampli?er negative feedback circuit 17,23,25,18,
`24,16.
`US. patent application Ser. No. 08/887,204 ?led Jul. 2,
`1997, and entitled SOLID STATE FINGERPRINT SEN
`35
`SOR PACKAGING APPARATUS AND METHOD
`(attorney docket number 97-B-036) shoWs a type of capaci
`tive ?ngerprint sensing apparatus having a structure that,
`When modi?ed, is usable in the present invention. This
`related patent application is incorporated herein by refer
`ence.
`The present invention relates to a manual or an object
`operable, solid state, capacitance sWitch. Capacitance-type
`sensors are generally knoWn.
`For example, the publication SENSORS AND
`45
`ACTUATORS, January/February 1989, no. 1/2, at pages
`141—153, contains an article entitled INTEGRATED TAC
`TILE IMAGER WITH AN INTRINSIC CONTOUR
`DETECTION OPTION that Was presented at the Fourth
`International Conference on Solid-State Sensors and Actua
`tors (Transducers ’87), Tokyo, Japan, Jun. 2—5, 1987. This
`article describes an integrated capacitive tactile imaging
`sensor that comprises a multi-layer construction having a
`bottom ceramic support, a 9-roW/9-column array of square
`aluminum electrodes that are contained on a silicon Wafer
`integrated circuit, a ?exible and isolating intermediate layer
`that is made up of natural rubber, a thin conductive rubber
`layer, and a top protective layer. In this device, capacitance
`depends upon local deformation of the natural rubber layer.
`The individual aluminum electrodes of this device provide
`capacitive measurement of an indentation pattern Within the
`natural rubber layer, this indentation being caused by a
`pressure distribution that acts on the top protective layer.
`Capacitance type sensors that operate to sense the minu
`tiae of a ?ngerprint are also knoWn.
`For example, the publication IEEE ELECTRON DEVICE
`LETTERS, VOL. 18, NO. 1, JANUARY 1997, pages 19—20,
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`US 6,225,711 B1
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`3
`the electrical insulator, and When a ?nger is brought into
`physical contact With this protective insulating ?lm, the
`metal electrodes are physically deformed, thereby selec
`tively changing the capacitance of the large number of
`capacitors in accordance With the ?ngerprint’s ridge/valley
`pattern. In a second type of sensor, the top surface of a rigid
`support carries a number of horiZontally spaced and ?at
`metal electrodes in a ?xed position. Placed above the plane
`of the metal electrodes is the sequential arrangement of a
`?exible insulator, a ?exible electrode, and a ?exible protec
`tive membrane. A capacitor is formed betWeen the top
`?exible electrode and each of the loWer and ?xed-position
`?at metal electrodes. When the end of a ?nger is brought into
`contact With the ?exible membrane, the ?exible electrode
`becomes Wavy in accordance With the ?ngerprints’ ridges/
`valleys pattern.
`In addition, US. Pat. No. 5,325,442, incorporated herein
`by reference, relates to a capacitance-type ?ngerprint sensor
`having a sensing pad that comprises a planar array of
`roW/column sensing elements having a pitch of about 100
`micrometers. Each sensing element is located at the inter
`section of a roW conductor and a column conductor, and in
`each sensing element, a sensing capacitor is made up of a
`planar sensing electrode that is spaced from a ?nger surface
`by Way of an insulating ?lm that overlies the sensing
`electrode. The plurality of sensing electrodes that make up
`the array are regularly spaced and equal-siZe rectangles.
`The sensing elements are fabricated using photolitho
`graphic processes, and each individual sensing element
`includes a Thin-Film-Transistor (TFT) in the form of a
`Field-Effect-Transistor
`Each FET gate is connected
`to a roW conductor, each FET source is connected to a
`column conductor, and each FET drain is connected to a
`sensing electrode.
`In one embodiment, each sensing element comprises a
`sensing capacitor that is formed betWeen a sensing electrode
`and the ?nger. In another embodiment, each sensing element
`includes an electrically isolated and conducting pad the is
`physically engaged by the ?nger.
`While prior devices as above described are generally
`useful for their limited intended use, a need remains in the
`art for an object operable solid state capacitance type sWitch
`having an improved construction, functionality and arrange
`ment.
`
`SUMMARY OF THE INVENTION
`The present invention provides a loW cost, ?ngertip
`operated, solid state, capacitance type, ampli?er sWitch
`having an improved construction and arrangement. The
`ampli?er sWitch of the present invention operates on the
`principle of detecting a capacity change that is induced by
`the physical contact of an object such as an ungrounded
`?ngertip With an external, or active, dielectric surface of the
`solid state ampli?er sWitch.
`While this invention Will be described making reference
`to the detection of a ?ngertip on, or closely adjacent to, a
`dielectric upper surface of a solid state sWitch in accordance
`With this invention, the scope and spirit of this invention
`should not be limited thereto since sWitches in accordance
`With the invention are useful to detect the presence/absence
`of other objects; for example, a moveable portion of a
`machine.
`One solid state ampli?er/detector circuit is provided for
`each sWitch in accordance With this invention. The input and
`output of the solid state ampli?er are respectively connected
`to tWo relatively large and ungrounded capacitor plates, or
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`electrodes, that are associated With, but physically and
`electrically isolated from, the sWitch’s external dielectric
`surface. A person’s ungrounded ?ngertip forms a third
`capacitor plate on, or closely adjacent to, the sWitch’s
`external surface. The solid state ampli?er circuit detects the
`presence of a ?ngertip on the sWitch’s external surface by
`Way of a change in capacitance that is created Within a
`compound, three electrode or three plate, capacitor that
`includes the tWo ungrounded capacitor plates and the
`ungrounded ?ngertip that is closely adjacent to, or resident
`on, the sWitch’s external surface.
`This compound capacitor is electrically connected to
`provide an ungrounded output-to-input negative feedback
`loop for a solid state signal-inverting ampli?er, Which ampli
`?er operates to convert a sensed change in capacitance value
`into an output voltage or output current.
`The solid state ampli?er sWitch in accordance With this
`invention, can be quite small; for example, about 110 micro
`meters square, depending upon the IC rules and line Widths
`of the fabrication technology that is employed. Of course,
`multiple and generally identical detector circuits can be
`placed physically and electrically in parallel in order to
`increase sensitivity and improve the robustness of sWitch
`detection.
`In addition, and as a feature of the invention, an Auto
`matic Gain Control (AGC) circuit may be integrated onto
`the solid state sWitch to periodically adjust the value of a
`reference voltage during quiescent times that the solid state
`sWitch is not operating, thereby alloWing the solid state
`sWitch to automatically adapt to various ambient conditions
`by Way of this voltage adjustment.
`Advantages of the present invention include high
`sensitivity, small sWitch area, solid state reliability, loW
`voltage operation, negligible poWer consumption, ability to
`operate in high/loW temperature and/or high/loW humidity
`environments, the ability to integrate the solid state sWitch
`of the present invention With other sensors, such as light
`sensors, to thereby provide a smart-sWitch, and the ability to
`integrate the solid state sWitch of the present invention With
`CMOS circuits, such as operational ampli?ers, A/D
`converters, D/A converters, microprocessors, etc.
`As a feature of the invention, the silicon portion of the
`solid state sWitch is coated-by a thin ?lm of electrically
`nonconducting plastic, thereby completely sealing this sili
`con portion from its physical environment.
`In a momentary-operation embodiment of the invention,
`the solid state sWitch is provided With three external leads
`that comprise an output lead, a poWer lead, and a ground
`potential lead. In this embodiment, the solid state sWitch
`operates to short the output lead to ground When the sWitch
`is closed or turned on. This sWitching action can be a
`momentary sWitching action, or the sWitch can be main
`tained turned on until a subsequent ?nger touch is experi
`enced. This latter function is implement by integrating a
`toggle ?ip-?op onto the sWitch’s integrated circuit, to
`thereby provide a single-bit memory.
`In another embodiment of the invention, the solid state
`sWitch is provided With four external leads; i.e., a contact-A
`lead, a contact-B lead, a poWer lead, and a ground potential
`lead. In this embodiment, contact-A lead and contact-B lead
`are opened/closed depending upon the operational state of
`the solid state sWitch. When the solid state sWitch includes
`a Diffused Metal Oxide Semiconductor (DMOS) poWer
`transistor that controls contact-A lead and contact-B lead, a
`conventional AC poWer line can be sWitched directly. As a
`feature of the invention, this embodiment includes a toggle
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`US 6,225,711 B1
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`5
`?ip-?op to provide a latched solid state switch that is closed
`by a ?rst ?nger/object touch, and is opened by the next
`?nger/object touch.
`As an additional feature of the present invention, a linear
`sWitch array, comprising a plurality of solid state sWitches of
`the present invention, is associated With a slider control
`knob. Selective positioning of this control knob relative to
`the linear array of solid state sWitches results in operation of
`a selected number of the plurality of solid state sWitches,
`much in the nature of analog control. In addition, a linear
`array of Light Emitting Diodes (LEDs) is placed adjacent to
`the control knob, so as to visually indicate the current
`position of the slider. These LEDs can be discrete and
`distinct from the solid state sWitches, or the LEDs can be
`integrated into the sWitches, for example, using a CMOS/
`LED process.
`As an additional feature of the invention, the above
`described momentary solid state sWitch is modi?ed to pro
`vide a temporal code detector that operates to detect a coded
`sequence of sWitch-taps, and a coded time interval betWeen
`adjacent taps, and to then provide a code-satis?ed output
`only When the correct number of taps, separated by the
`correct time intervals, has been received by the momentary
`solid state sWitch.
`These and other objects, advantages and features of the
`present invention Will be apparent to those of skill in the art
`upon reference to the folloWing detailed description, Which
`description makes reference to the draWing.
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`BRIEF DESCRIPTION OF THE DRAWING
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`FIGS. 1, 2 and 3 are taken from the above-noted related
`application Ser. No. 08/799,548 by Marco Tartagni, and
`FIG. 2 shoWs the electrical circuitry of a solid state ampli?er,
`a modi?cation of Which is used in the present invention.
`FIG. 4 shoWs a ?rst momentary-sWitch embodiment of
`the invention having three external leads that comprise an
`output lead, a poWer lead, and a ground potential lead, this
`embodiment operating to short the output lead to ground
`When the sWitch is closed or turned on.
`FIG. 5 shoWs a second latched-sWitch embodiment of the
`invention also having three external leads that comprise an
`output lead, a poWer lead, and a ground potential lead
`Wherein the sWitch is maintained turned on until a subse
`quent ?nger touch is experienced by operation of a toggle
`?ip-?op that is integrated onto the sWitch’s IC to provide a
`single-bit of memory.
`FIG. 6 shoWs a third embodiment of the invention
`Wherein a DMOS solid state output poWer transistor is
`provided, so that the FIG. 6 sWitch has four external leads,
`Wires or electrical conductors, ie an output contact-A lead,
`an output contact-B lead, a poWer lead, and a ground
`potential lead, Wherein a circuit extending betWeen
`contact-A lead and contact-B lead is opened/closed depend
`ing upon the on/off operational state of the solid state sWitch,
`and Wherein the sWitch’s DMOS poWer transistor controls
`contact-A lead and contact-B lead such that a conventional
`AC poWer line can be sWitched directly by opening/closing
`the poWer transistor circuit that extends betWeen leads A and
`B.
`FIG. 7 shoWs an additional feature of the present inven
`tion Wherein a linear array comprising the plurality N of
`solid state sWitches in accordance With FIG. 5 or 6, is
`associated With an automatically moved, or manually moved
`slider control knob, such that X-direction positioning of this
`control knob relative to the linear array results in operation
`of a selected number of the solid state sWitches, much in the
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`nature of analog control. In this embodiment, a linear array
`of light emitting diodes, or LEDs, is placed adjacent to the
`slider so as to visually indicate the current position of the
`slider, Wherein the LEDs can be discrete and distinct from
`the solid state sWitches, or Wherein the LEDs can be
`integrated into the sWitches themselves; for example, using
`a CMOS/LED process.
`FIG. 8 is an embodiment of the invention Wherein FIG.
`4’s solid state sWitch is modi?ed by adding an AGC netWork
`to adjust the value of reference voltage Vr during quiescent
`times during Which the sWitch is not operating, thereby
`alloWing the sWitch to adapt to various ambient conditions
`by Way of this voltage adjustment.
`FIG. 9 shoWs an embodiment of this invention that uses
`the FIG. 4 sWitch as a temporal tap-code detector.
`FIG. 10 shoWs another embodiment of this invention that
`uses the FIG. 4 sWitch as a temporal tap-code detector.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`FIGS. 1, 2 and 3 are taken from the above-noted related
`application Ser. No. 08/799,548 by Marco Tartagni, and
`FIG. 2 thereof shoWs the electrical circuitry of a solid state
`ampli?er, a modi?cation of Which is used in the present
`invention.
`FIG. 1 is a top vieW of an IC device 1 that includes a
`generally planar, multiple pixel, multiple roW/column, array
`3 having a relatively large number of solid state capacitive
`sensor cells 2 that operate to provide an electrical output 10
`that, in accordance With application Ser. No. 08/799,548,
`comprises a multiple pixel ?ngerprint pattern. As shoWn,
`FIG. 1 is taken in the X-Y plane.
`Array 3 contains the number N of horiZontal or
`X-direction extending roWs of individual capacitance sensor
`cells 2, each roW having the number M of individual sensor
`cells 2 therein, and array 3 contains the number M of
`vertically or Y-direction extending columns of individual
`capacitance sensor cells 2, each column having the number
`N of individual sensor cells 2 therein, Wherein the numbers
`N and M are integers that may of may not be equal to each
`other. The number of individual picture elements, pixels, or
`cells 2 Within array 3 is quite large, and equals the product
`of M><N. An example is 512x512 pixels or cells 2 Within
`array 3, array 3 being of a physical siZe of about 20 mm to
`about 25 mm.
`Each individual sensor cell 2 Within array 3 is addressable
`by virtue the cell being physically located at the intersection
`of a roW/column of array 3. The manner in Which the
`individual sensor cells 2 of array 3 are addressed and read
`out in order to digitiZe a ?ngerprint pattern are Well knoWn
`to those of skill in the art.
`IC device 1 includes a horiZontal scanning stage, or
`netWork 5, and a vertical scanning stage or netWork 6 for
`sequentially interrogating or reading one cell 2 at a time,
`according to a predetermined scanning pattern. Preferably,
`stages 5 and 6 comprise shift registers, or decoders, that
`operate to interrogate the FIG. 2 outputs 17 of cells 2
`sequentially.
`IC device 1 also includes a supply/logic stage or netWork
`7 that operates to supply the IC device components, includ
`ing all cells 2, With the necessary operating voltages, and to
`control the sequence of steps that are necessary for operation
`of IC device 1. In particular, a DC voltage source 12
`provides a DC reference voltage VR that is reference to
`ground potential at 100. A buffer 8 is connected to the
`
`Neodron Ltd.
`Exhibit 2007
`IPR2020-00406
`
`Page 12 of 16
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`

`

`US 6,225,711 B1
`
`7
`outputs 17 of all cells 2. Ground referenced output 10 of
`buffer 8 comprises the sequentially arranged output of IC
`device 1, the signal at output 10 being controlled by opera
`tion of scanning stages 5 and 6.
`FIG. 2 schematically shoWs the ampli?er circuitry of a
`single cell 2 of FIG. 1’s array 3, all cells 2 being generally
`identical in construction and arrangement. Each cell 2
`includes a loW-poWer, signal inverting, ampli?er 13.
`In a ?ngerprint acquisition process in accordance With the
`above-noted related patent application Ser. No. 08/799,548
`by Marco Tartagni, each ampli?er 13 had an exemplary gain
`of from about 1000 to about 2000.
`The solid state capacitive sWitch of the present invention
`can be used in a large number of operating environments. As
`a result, the gain of ampli?ers such as ampli?er 13 are tuned,
`or adjusted, such that the speed of operation of the solid state
`capacitive sWitch is compatible With the needs of the sWitch
`application being served by the sWitch. For eXample, usually
`the required speed of sWitch operation is quite loW, and as
`a result, ampli?er gain can be considerably loWer than the
`above noted range.
`Terminal 21 comprise the input to the circuit of cell 2, and
`terminal 21 and input capacitor 20 connect to input 16 of
`solid state ampli?er 13. Terminal 17 comprises the output of
`cell 2 and ampli?er 13. Each cell 2 also includes tWo
`ungrounded X-Y planar armatures, or metal capacitor plates
`23,24, that are of generally equal area and are horiZontally,
`or X-direction spaced from each other Within a common
`X-Y horiZontal plane. A thin dielectric layer 25 covers
`capacitor plates 23,24, and the upper horiZontal surface 125
`of layer 25 provides an active array surface for physical
`contact by the skin surface of a ?nger 18 Whose ?ngerprint
`is to be sensed or determined. Dielectric layer 25 may cover
`the entire face of the upper portion of IC device 1 that
`includes array 3 and its individual cells 2.
`In use, a ?ngertip 18 is placed on the upper surface 125
`of array 3’s dielectric layer 25. Fingertip 18 thereby forms
`an ungrounded armature, or electrode, that vertically over
`lies and faces the top, X-Y planar, surfaces of capacitor
`plates 23,24. Fingertip 18 operates to de?ne With plates
`23,24 the ?rst capacitor 34 of FIG. 3, and the second
`capacitor 33 of FIG. 3, Which series connected compound
`capacitors 33,34 are connected in negative feedback fashion
`from ampli?er output 17 to ampli?er input 16.
`Each cell 2 also includes a normally open start, reset, or
`control sWitch 19, preferably in the form of a Metal Oxide
`Semiconductor (MOS) sWitch. SWitch 19 selectively and
`momentarily operates to short ampli?er input 16 to ampli?er
`output 17. SWitch 19 is controlled by a control signal “R”
`that is provided by FIG. 1’s supply and logic unit 7. At the
`start of a ?ngerprint acquisition operation, sWitches 19 of all
`array cells 2 are momentarily closed, and the voltage level
`at all cell inputs 21 is maintained at a constant magnitude.
`In this Way, the input voltage of all cells 2 is brought to the
`same potential as the cell’s output voltage.
`Shortly thereafter, supply and logic unit 7 operates to open
`all reset sWitches 19, and to supply all cell inputs 21 With a
`step voltage that is equal in magnitude to reference voltage
`VR. An electrical charge is noW induced at each of the cell
`input capacitors 20, thus permitting the reading of the local
`and individual Z-direction cell distances “d” that eXist
`betWeen a cell’s capacitor plates 23,24 and that cell’s
`overlying ?ngertip ridge/valley surface 18.
`Scanning stages 5,6 of FIG. 1 noW operate to sequentially
`enable the reading, or interrogation, of the many cells 2
`Within array 3. In this Way, buffer 8 operates to provide an
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`output 10 in the form of a sequence of gray levels of voltage
`that comprise a three-dimensional readout and display of the
`?ngertip ridge/valley surface 18 of the ?nger that is cur
`rently resident on the top surface 125 of array 3.
`FIG. 3 is an equivalent circuit of the single cell circuit
`shoWn in FIG. 2. The input capacitance of ampli?er 13 is
`shoWn at 30, the output capacitance of ampli?er 13 is shoWn
`at 31, and the tWo above-mentioned series connected and
`touch-sensitive capacitors are shoWn at 33,34.
`FIGS. 4—6 and 8 shoW embodiments of the present
`invention Wherein structural elements that are common to
`above-described FIGS. 1—3 are identi?ed by the use of
`common reference numerals. Each of the FIGS. 4—6 and 8
`solid state sWitch embodiments, as Well as the arrangements
`of FIGS. 7, 9 and 10, may be constructed in accordance With
`the packaging scheme taught in the above-referenced appli
`cation entitled SOLID STATE FINGERPRINT SENSOR
`PACKAGING APPARATUS AND METHOD.
`In these FIGS. 4—6 and 8 embodiments of the invention,
`dielectric-buried or dielectric-covered, capacitor plates
`23,24 have an exemplary X-Y area as large as about 1 mm
`by 1 mm, or as small as about 50 micrometers by 50
`micrometers. In either case, the Z-direction thickness of
`capacitor plates 23,24 is about 1 micrometer. HoWever, this
`parameter varies based upon dimensions that are derived
`from the fabrication process that is used to produce the
`device.
`With reference to FIGS. 4—6 and 8, each of the solid state
`sWitches 400,500,600 includes a cycling netWork 800 that
`operates in repeating cycles to sample the state of that
`sWitch’s composite object-sensitive capacitor 33,34. An
`eXemplary cycling rate is from about 1 to about 60 HZ.
`In the operation of FIGS. 4—6 and 8, each cycle