United States Patent
`
`
`Gerpheide et al.
`
`
`
`
`[19]
`
`
`
`
`[11] Patent Number:
`
`
`
`[45] Date of Patent:
`
`I|||l|ll||lI||Illl|||||||l|||||||||l|llllllllllllllllllllllllllllllllllllll
`USO05565658A
`
`
`
`
`5,565,658
`
`
`
`Oct. 15, 1996
`
`[54‘ CAPACITANCE—BASED PROXIMITY WITH
`
`
`
`INTERFERENCE REJECTION APPARATUS
`
`
`AND NIETHODS
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Inventors: George E. Gerpheide; Michael D.
`
`
`
`
`Layton, both of Salt Lake City, Utah
`
`
`
`
`
`
`
`
`Assignee: Cirque Corporation, Salt Lake City,
`
`
`
`
`
`Utah
`
`
`
`
`Appl. No.: 351,008
`
`
`
`
`
`
`Filed:
`
`
`DEC. 7, 1994
`
`
`
`Related U-S- Application Data
`
`
`
`
`
`
`
`CDminuafion_in»pm of Ser No 193 275 Feb 8 1994 Pat
`
`
`NO. 5,478,170’ which is a c'Omi‘nua[i’on 0% Ser_'N’0_ 914043;
`11,1, 13, 1992, pat No_ 5,305,017,
`
`
`
`
`
`
`
`
`
`
`Int. CL5 ____________________________________________________ G08‘: 21/00
`
`
`
`
`U S C]
`178/19_ 345/174
`Fi'el'd 0;.
`178/1;; 19 20_
`"""""""""""""""""
`
`
`
`
`
`
`
`
`
`
`
`345/168 173 174_ 328/5_ 342/16
`’
`i
`’
`’
`
`
`
`
`References Cited
`
`
`U.s. PATENT DOCUMENTS
`
`
`
`12/1980 Waldron .................................... .. 325/5
`
`
`
`
`
`
`4,237,421
`
`
`4,371,746
`4,476,463
`4,845,682
`5,053,757
`5,305,017
`
`
`
`
`
`
`
`................................ 178/18
`2/1983 Pepper, Jr.
`
`
`
`
`10/1984 Ng et al.
`............
`
`
`
`
`7/1989 Boozer et al.
`.
`
`
`11)/1991 Meadows ..
`
`
`4/1994 Gerpheide .
`
`
`
`
`
`342/16 X
`
`
`178/18 X
`
`
`.. 345/174
`
`
`
`
`
`Primary Examz'ner—Stephen Chin
`
`
`
`Assistant Examiner—Paul Loomis
`
`
`
`Attomey, Agent, or Firm—Thorpe, North & Western
`
`
`
`
`
`
`
`
`[57]
`
`
`
`ABSTRACT
`
`
`
`Apparatus and method for a capacitancebased proximity
`
`
`
`
`
`
`
`
`
`
`
`
`sensor with interference rejection. A pair of electrode arrays
`
`
`
`
`
`
`
`establish acapacitance on a touch detection pad, the capaci-
`tance varying with movement of a conductive Ob_]€CT. near
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`the pad. The capacitance variations are measured synchro-
`
`
`
`
`
`
`
`
`nously with a reference frequency signal to thus provide a
`measure of the position of the object, Electrical interference
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`is rejected by producing a reference frequency signal which
`is not coherent with the interference.
`
`
`
`
`
`
`
`14 C1aiIns.8 Drawing Sheets
`
`
`
`
`
`
`Electrode
`
`
`
`
`\ .1:£_’f_
`
`14
`
`
`
`Capacitance
`
`Measurements
`
`
`
`
`
`
`
`
`Synchronous
`Electrode
`
`Capacitance
`
`Measurement
`
`
`
`
`
`
`
`Position
`
`Locator
`
`
`
`
`
`
`
`Position
`
`
`Signals
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Reference
`Frequency
`Generator
`
`
`
`n‘;“r}‘:';‘1:.
`
`
`
`
`
`
`
`
`
`
`Frequency
`Signal
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 1 of 15
`
`SAMSUNG EXHIBIT 1012
`
`

`
`U.S. Patent
`
`69915,1LC0
`
`Sheet 1 of 8
`
`5,565,658
`
`:o.....8m_
`flmtflw[I1
`
`§.....8m
`
`MOHWOOH
`
`mozmtomnmo
`
`m__:mEm::wmuE
`
`E
`
`§..e5.%5
`
`Qfiohwufim "I'I
`
`
`
`.:EEo.Smm2\<.
`
`II''§--‘h
`
`Illlrlll
`
`V‘~..-‘~‘~NIIHH
`
`obohoom
`
`outououwt
`
`Auumzumxk
`
`..2m..o:mG
`
`£\m_.
`
`_.2.m..m
`
`Aucmauouk
`
`uamcm
`
`
`
`\N:G.~@¢0EOLO».¢......\
`
`Page 2 of 15
`
`

`
`
`
`U.S. Patent
`
`Oct. 15, 1996
`
`
`
`
`
`Sheet 2 of 8
`
`
`5,565,658
`
`
`
`
`
`
`
`X Electrodes
`
`
`
`
`
`
`E?
`II
`2!
`ll
`32
`_II
`fll
`
`
`
`Y Electrodes
`
`
`
`\ N
`
`.
`
`
`
`Insulator 31
`
`
`
`Insulator 32
`
`
`
`InSU,atOr 33
`
`
`26
`
`
`
`
`
`Insulating Overlay
`
`
`
`X Electrodes
`
`
`
`YEIectrodes
`
`21
`
`
`
`VIIIIIIIIIIIIIIIIIIAIYIZ
`
`
`
`
`
`
`
`GroundfllIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIJIIIIIIIII
`Plane I-
`
`LCQCCC Q‘
`
`
`
`
`
`
`
`
`
`
`Component Traces
`
`
`
`Fig. 2b
`
`Page 3 of 15
`
`

`
`U.S. Patent
`
`
`
`
`Oct. 15, 1996
`
`
`
`Sheet 3 of 8
`
`
`5,565,658
`
`
`
`
`
`"' I'll
`
`-
`
`TIA
`
`
`VJ
`
`VII
`
`
`
`VI]
`
`VII *
`
`
`
`
`
`YCIICIIICCICCIIICZCCL
`
`
`
`
`
`
`Insulating Overlay
`X Electrode
`
`
`Conductive Ink
`
`Insuiating Ink
`
`
`Y Electrode
`
`
`conductive Ink
`
`
`
`insulating Ink
`Ground Plane
`
`
`
`
`
`
`
`X Electrodes
`
`
`
`
`
`
`
`Integrated Circuitry
`
`
`
`Printed Circuit Board
`
`
`Substrate
`
`
`
`
`
`
`Printed Wiring
`
`
`
`
`
`
`
`Page 4 of 15
`
`

`
`U.S. Patent
`
`69915,1f"c0
`
`Sheet 4 of 8
`
`5,565,658
`
`o>.EumQmO_IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII.
`mmml.204m:o:o.Eu§m..:uEo.Smmo:_.
`
`
`
`IIL
`
`
`
`LOum3tcEuQ«:0-.20__W
`.:o.aE..Q4.“vs-/.-
`
`omumco
`
`gfimcmt.
`
`__.3E.5
`
`cutmtumnmo
`
`~:uEu.Smmus.
`
`ace...»
`
`:m.a:Eot..&
`
`Y Electrodes
`
`muuo.:....o.mX
`
`~m=m..m
`
`
`
`«Baumu.a....5§m
`
`
`
`.._:.:n%E_.u£m
`
`.m=t.S
`
`
`
`.m:m..m.G=.§u2.._.
`
`wutouuuomV..Q~umsgaumuou
`
`
`
`:o.=._molEOLK
`
`Page 5 of 15
`
`

`
`U.S. Patent
`
`..l.C0
`
`69915.,1
`
`Sheet 5 of 8
`
`5,565,658
`
`mutmtomumo
`
`~:mEP.:mmm§<
`
`m__m:m..m
`
`m=o:o.Eu:>m
`
`.6_..m3boEmQ
`
`w~:oE2m
`
`oocmtumqmo
`
`wC¢EOL3wW0§<
`
`m..:mE2m
`
`muohcmm
`
`>m.:<
`
`m>.tQ
`
`u3m:m
`
`=..=m..m
`
`oozmuogmm
`
`>.u=w=uw.E
`
`.m=m...m.
`
`Page 6 of 15
`
`

`
`
`
`U.S. Patent
`
`Oct. 15, 1996
`
`
`
`
`Sheet 6 of 8
`
`
`5,565,658
`
`
`
`AVout=AVdrive x
`
`
`
`Drive
`
`
`
`
`AVout=AVdrivex ( cm )
`
`
`
`C’
`
`Drive
`
`
`AVout=AVdrivex< C9
`
`|_}__L_
`
`Drive
`
`Cg+Cr
`
`
`
`)
`
`
`AVaut=AVdrive x (C-q+cr)
`C9
`
`
`
`
`
`
`
`
`Drive
`
`Page 7 of 15
`
`

`
`U.S. Patent
`
`
`
`
`Oct. 15, 1996
`
`
`
`
`Sheet 7 of 3
`
`
`5,565,658
`
`
`
`
`
`
`
`
`
`
`
`Capacitance
`Measurements
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`pas,-t,-0,,
`
`5,-gna,
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Reference
`
`Frequency
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Oscillator
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Microcontroller
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Frequency
`
`Select
`L
`
`Interference
`Evaluation
`
`
`
`
`
`
`
`
`
`
`
`
`Microprocessor
`
`
`
`
`Z 102
`
`
`
`Page 8 of 15
`
`

`
`
`U.S. Patent
`
`
`
`
`Oct. 15, 1996
`
`
`
`
`Sheet 8 of 8
`
`5,565,658
`
`
`
`
`
`
`
`
`
`Pseudo
`
`Number
`
`. Random
`
`
`
`
`Generator
`
`
`
`Reference
`Frequency
`
`Signal
`
`
`
`
`
`
`
`
`
`
`
`Oscillator
`
`
`
`
`
`
`
`Page 9 of 15
`
`

`
`5,565,658
`
`1
`
`CAPACITANCE-BASED PROXIMITY WITH
`
`
`
`INTERFERENCE REJECTION APPARATUS
`
`
`
`AND METHODS
`
`
`
`The following patent is a continuation-in-part patent of
`
`
`
`
`
`U.S. patent application Ser. No. 08/193,275, filed Feb. 8,
`
`
`
`
`
`
`
`
`1994, now U.S. Pat. No. 5,478,170, which is a continuation
`
`
`
`
`
`
`
`
`of Ser. No. 914,043, filed Jul. 13, 1992, now U.S. Pat. No.
`
`
`
`
`
`
`
`
`
`
`
`
`5,305,017.
`
`This invention relates generally to apparatus and meth-
`
`
`
`
`
`
`
`ods for touch sensitive input devices, and more particularly,
`
`
`
`
`
`
`
`
`
`to apparatus and methods for capacitance-based touch detec-
`
`
`
`
`
`
`
`
`tion wherein electrical interference is effectively rejected
`
`
`
`
`
`
`from the detection system.
`‘
`
`
`
`
`
`BACKGROUND OF THE INVENTION
`
`
`
`Numerous prior art devices and systems exist by which
`
`
`
`
`
`
`
`
`tactile sensing is used to provide data input
`to a data
`
`
`
`
`
`
`
`
`processor. Such devices are used in place of common
`
`
`
`
`
`
`
`
`pointing devices (such as a “mouse" or stylus) to provide
`
`
`
`
`
`
`
`data input by finger positioning on a pad or display device.
`
`
`
`
`
`
`
`These devices sense finger position by a capacitive touch
`
`
`
`
`
`
`
`
`pad wherein scanning signals are applied to the pad and
`
`
`
`
`
`
`
`
`
`variations in capacitance caused by a finger touching or
`
`
`
`
`
`
`
`
`approaching the pad are detected. By sensing the finger
`
`
`
`
`
`
`
`
`
`position at successive times, the motion of the finger can be
`
`
`
`
`
`
`
`
`detected. This sensing apparatus has application for control-
`
`
`
`
`
`
`
`
`ling a computer screen cursor. More generally it can provide
`
`
`
`
`
`
`
`
`a variety of electrical equipment with information corre-
`
`
`
`
`
`
`
`
`sponding to finger movements, gestures, positions, writing,
`
`
`
`
`
`
`signatures and drawing motions.
`
`
`
`
`In U.S. Pat. No. 4,698,461, Meadows et al., a- touch
`
`
`
`
`
`
`
`
`
`surface is covered with a layer of invariant resistivity. Panel
`
`
`
`
`
`
`
`scanning signals are applied to excite selected touch surface
`
`
`
`
`
`
`
`
`edges so as to establish an alternating current voltage
`
`
`
`
`
`
`
`
`
`gradient across the panel surface. When the surface is
`
`
`
`
`
`
`
`touched, a touch current
`llows from each excited edge
`
`
`
`
`
`
`
`
`through the resistive surface and is then coupled to a user’s
`
`
`
`
`
`
`
`
`finger (by capacitance or conduction), through a uscr’s body,
`
`
`
`
`
`
`
`and finally coupled by the user’s body capacitance to earth
`
`
`
`
`
`
`
`
`ground potential. Different scanning sequences and modes
`
`
`
`
`
`
`
`of voltage are applied to the edges, and in each case the
`
`
`
`
`
`
`
`
`
`
`currents are measured. It is possible to determine the loca-
`
`
`
`
`
`
`
`
`tion of touch by measuring these currents. In particular, the
`
`
`
`
`
`
`
`
`physical parameter which indicates touch location is the
`
`
`
`
`
`
`
`resistance from the edges to the point of touch on the
`
`
`
`
`
`
`
`
`
`
`surface. This resistance varies as the touch point is closer or
`
`
`
`
`
`
`
`
`farther from each edge. For this system, the term “capacitive
`
`
`
`
`
`
`
`
`
`
`touch pad” may be a misnomer because capacitance is
`
`
`
`
`
`
`involved as a means of coupling current from the surface
`
`
`
`
`
`
`
`touch point through the user’s finger but is not the parameter
`
`
`
`
`
`
`
`
`
`
`indicative of finger position. A disadvantage of this inven-
`
`
`
`
`
`
`
`tion is that accurate touch location measurement depends on
`
`
`
`
`
`
`
`uniform resistivity of the surface. Fabricating such a uni-
`
`
`
`
`
`
`
`
`formly resistive surface layer can be difiicult and expensive,
`
`
`
`
`
`
`
`
`and require special fabrication methods and equipment.
`
`
`
`
`
`
`
`The panel of the Meadows ’46l patent also includes
`
`
`
`
`
`
`
`
`
`circuitry for “nulling”, or ofisetting to zero,
`the touch
`
`
`
`
`
`
`
`
`
`currents which are present when the panel is not touched.
`
`
`
`
`
`
`
`
`
`This nulling can be accomplished while the panel operates,
`
`
`
`
`
`
`
`
`and allows touches which generate a relatively weak signal,
`
`
`
`
`
`
`
`
`such as from a gloved finger, to be more accurately deter-
`
`
`
`
`
`
`
`
`mined. The Meadows ’46l panel also includes circuitry for
`
`
`
`
`
`
`
`
`
`automatically shifting the frequency of panel scanning sig-
`
`
`
`
`
`
`
`nals away from spectra of spurious signals, such as those
`
`
`
`
`
`
`
`
`developed by cathode-ray tube transformers, which may be
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`2
`
`present in the environment. The panel seeks to avoid inter-
`
`
`
`
`
`
`
`
`ference from the spurious signals, which could happen if the
`
`
`
`
`
`
`
`
`
`frequency of scanning was nearly equal
`to that of the
`
`
`
`
`
`
`
`
`
`
`spurious signals. A microcontroller determines whether the
`
`
`
`
`
`
`scanning frequency should be shifted by monitoring the rate
`
`
`
`
`
`
`
`at which adjustments are required in nulling of the touch
`
`
`
`
`
`
`
`
`
`currents, as described above. The only means described for
`
`
`
`
`
`
`
`
`
`generating frequency control signals is based on this nulling
`
`
`
`
`
`
`
`adjustment.
`
`U.S. Pat. No. 4,922,061, Meadows et al., is similar to the
`
`
`
`
`
`
`
`
`
`Meadows ’461 patent in that the touch panel determines
`
`
`
`
`
`
`
`
`
`touch location based on variations in resistance, not capaci-
`
`
`
`
`
`
`
`tance. This is particularly evident from FIG. 2 where the
`
`
`
`
`
`
`
`
`resistances from edge to touch point are shown as Kx times
`
`
`
`
`
`
`
`
`Rx, where Kx is corresponds to the distance indicated by
`
`
`
`
`
`
`76A. The apparatus uses a measurement signal of a fre-
`
`
`
`
`
`
`
`
`quency that varies in a substantially random manner, thus
`
`
`
`
`
`
`
`
`reducing susceptibility to interference from spurious elec-
`
`
`
`
`
`
`
`tromagnetic spectra.
`
`
`U.S. Pat. No. 4,700,022, Salvador, describes an array of
`
`
`
`
`
`
`
`
`detecting conductive strips, each laid between resistive
`
`
`
`
`
`
`
`emitting strips. The finger actually makes electrical contact
`
`
`
`
`
`
`
`
`from an emitting strip to detecting strip. Touch location is
`
`
`
`
`
`
`
`
`determined from resistance variation (as with Meadows ’46l
`
`
`
`
`
`
`
`
`and ’O61 above) in the strip contacted by the finger. Averages
`
`
`
`
`
`
`
`
`are taken of a certain number of synchronous samples. A
`
`
`
`
`
`
`design formula is presented to choose a sampling frequency
`
`
`
`
`
`
`so that it is not a multiple of the most undesired predeter-
`
`
`
`
`
`
`
`
`
`mined interfering signal. No suggestion is made that sam-
`
`
`
`
`
`
`
`
`pling frequency is adjusted or adapts automatically.
`
`
`
`
`
`In U.S. Pat. No. 5,305,017, Gerpheide, touch location is
`
`
`
`
`
`
`
`
`determined by true capacitance variation, instead of resis-
`
`
`
`
`
`
`tance variation, using a plurality of electrode strips forming
`
`
`
`
`
`
`
`virtual electrodes. This approach eliminates the necessity of
`
`
`
`
`
`
`
`a coating having uniform resistance across a display screen.
`
`
`
`
`
`
`
`
`However, such a capacitance-based detection device may
`
`
`
`
`
`
`suffer from electrical background interference from its sur-
`
`
`
`
`
`
`
`roundings, which is coupled onto the sensing electrodes and
`
`
`
`
`
`
`
`
`interferes with position detection. These spurious signals
`
`
`
`
`
`
`
`cause troublesome interference with the detection of finger
`
`
`
`
`
`
`
`positioning. The device operator may even act as an antenna
`
`
`
`
`
`
`
`
`for electrical interference which may cause a false charge
`
`
`
`
`
`
`
`
`injection or depletion from the detecting electrodes.
`
`
`
`
`
`
`Accordingly, there is a need for a touch detection system
`
`
`
`
`
`
`which has the following characteristics:
`
`
`
`
`
`(1) the touch location is determined without the need of
`
`
`
`
`
`
`
`
`resistance variation so as to avoid the high cost of
`
`
`
`
`
`
`
`
`
`
`requiring uniform resistance during fabrication;
`
`
`
`
`
`(2) the touch location is measured in a manner indepen-
`
`
`
`
`
`
`
`dent of resistance of the electrodes or their connecting
`
`
`
`
`
`
`wiring,
`thus broadening the range of materials and
`
`
`
`
`
`
`
`
`processes which may be used for fabrication; and
`
`
`
`
`
`
`
`(3) electrical interference signals are rejected and elimi-
`
`
`
`
`
`
`
`
`nated from the detection system regardless of their
`
`
`
`
`
`
`
`
`frequency and without requiring possibly expensive
`
`
`
`
`
`
`nulling apparatus.
`
`
`SUMMARY OF THE INVENTION
`
`
`
`The present invention employs a touch location device
`
`
`
`
`
`
`
`having true capacitance variation by using insulated elec-
`
`
`
`
`
`
`
`
`trode arrays to form virtual electrodes.’ The capacitance
`
`
`
`
`
`
`
`
`variation is measured by means independent of the resis-
`
`
`
`
`
`
`tance of the electrodes, so as to eliminate that parameter as
`
`
`
`
`
`
`
`a fabrication consideration. The electrical
`interference is
`
`
`
`
`
`
`eliminated regardless of frequency to provide a clear detec-
`
`
`
`
`
`
`
`
`
`Page 10 of 15
`
`

`
`5,565,658
`
`
`
`3
`
`
`
`tion signal.
`
`
`invention
`An illustrative embodiment of the present
`
`
`
`
`
`
`
`includes an electrode array for developing capacitanees
`
`
`
`
`
`
`
`which vary with movement of an object (such as finger,
`
`
`
`
`
`
`
`
`
`other body part, conductive stylus, etc.) near the array, a
`
`
`
`
`
`
`
`
`
`synchronous capacitance measurement element which mea-
`
`
`
`
`
`
`sures variation in the capacitances, such measurements
`
`
`
`
`
`
`
`being synchronized with a reference frequency signal, and a
`
`
`
`
`
`
`
`reference frequency signal generator for generating a refer-
`
`
`
`
`
`
`
`ence frequency signal which is not coherent with electrical
`
`
`
`
`
`
`
`
`interference which could otherwise interfere with capaci-
`
`
`
`
`
`
`
`tance measurements and thus position location.
`
`
`
`
`
`
`Interference rejection is carried out by generating a ref-
`
`
`
`
`
`
`erence frequency signal whose frequency is different from
`
`
`
`
`
`
`
`the interference frequency. Altemately, the reference signal
`
`
`
`
`
`
`
`is generated with random frequencies so as not
`to be
`
`
`
`
`
`
`
`
`
`
`coherent with the interference frequencies and thus the
`
`
`
`
`
`
`
`
`electrical interference is effectively rejected.
`
`
`
`
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`
`
`
`FIG. 1 is a block diagram of a capacitance variation
`
`
`
`
`
`position measuring device made in accordance with the
`
`
`
`
`
`
`
`principles of the present invention;
`
`
`
`
`
`FIG. 2A is a plan view of one illustrative embodiment of
`
`
`
`
`
`
`the electrode array shown in FIG. 1;
`
`
`
`
`
`FIG. 2B is a side, cross-sectional view of one illustrative
`
`
`
`
`
`
`embodiment of the electrode array of FIG. 2A;
`
`
`
`
`
`
`
`FIG. 3A is a side, cross-sectional view of another embodi-
`
`
`
`
`
`
`ment of the electrode array of FIG. 1;
`
`
`
`
`
`FIG. 3B is a plan view of the electrode array of FIG. 3A;
`
`
`
`
`
`
`
`
`FIG. 4 is a schematic of one embodiment of the synchro-
`
`
`
`
`
`
`nous electrode capacitance measurement device of FIG. 1;
`
`
`
`
`
`
`FIG. 5 is a schematic of another embodiment of the
`
`
`
`
`
`
`synchronous electrode capacitance measurement device of
`
`
`
`
`
`
`FIG. 1;
`
`FIGS. 6A—6D are circuit diagrams of alternative embodi-
`
`
`
`
`
`
`ments of the capacitance measurement elements shown in
`
`
`
`
`
`
`FIGS. 4 and 5;
`
`
`FIG. 7 is a block diagram of one embodiment of the
`
`
`
`
`
`reference frequency generator shown in FIG. 1; and
`
`
`
`
`
`
`FIG. 8 is a block diagram showing an alternative embodi-
`
`
`
`
`
`
`ment of the reference frequency generator shown in FIG. 1.
`
`
`
`
`
`
`
`
`
`
`
`
`DETAILED DESCRIPTION OF PREFERRED
`
`
`EMBODIMENTS
`
`FIG. 1 shows the essential elements of a capacitance
`
`
`
`
`
`
`
`variation finger (or other conductive body or non-body part)
`
`
`
`
`
`
`
`
`position sensing system 10, made in accordance with the
`
`
`
`
`
`
`
`
`invention. An electrode array 12 includes a plurality of
`
`
`
`
`
`
`
`
`layers of conductive electrode strips. The electrodes and the
`
`
`
`
`
`
`
`
`wiring connecting them to the device may have substantial
`
`
`
`
`
`
`
`
`resistance, which permits a variety of materials and pro-
`
`
`
`
`
`
`
`
`cesses to be used for fabricating them. The electrodes are
`
`
`
`
`
`
`
`
`
`electrically insulated from one another. Mutual capacitance
`
`
`
`
`
`
`
`exists between each two of the electrodes, and stray capaci-
`
`
`
`
`
`
`
`
`
`tance exists between each of the electrodes and ground. A
`
`
`
`
`
`
`
`
`finger positioned in proximity to the array alters these
`
`
`
`
`
`
`
`
`
`mutual and stray capacitance values. The degree of alter-
`
`
`
`
`
`
`
`
`ation depends on the position of the finger with respect to
`
`
`
`
`
`
`
`
`electrodes. In general, the alteration is greater when the
`
`
`
`
`
`
`
`
`
`finger is closer to the electrode in question.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`4
`
`A synchronous electrode capacitance measurement unit
`
`
`
`
`
`
`14 is connected to the electrode array 12 and determines
`
`
`
`
`
`
`
`
`selected mutual and/or stray capacitance values associated
`
`
`
`
`
`
`
`with the electrodes. To minimize interference, a number of
`
`
`
`
`
`
`measurements are performed by unit 14 with timing syn-
`
`
`
`
`
`
`
`
`chronized to a reference frequency signal provided by
`
`
`
`
`
`
`
`reference frequency generator 16. The desired capacitance
`
`
`
`
`
`
`
`value is determined by integrating, averaging, or in more
`
`
`
`
`
`
`general
`terms, by filtering the individual measurements
`
`
`
`
`
`
`
`made by unit 14. In this way, interference in the measure-
`
`
`
`
`
`
`
`
`
`ment is substantially rejected except for spurious signals
`
`
`
`
`
`
`
`having strong frequency spectra near the reference fre-
`
`
`
`
`
`
`
`
`queney.
`
`The reference frequency generator 16 attempts to auto-
`
`
`
`
`
`
`
`matically select and generate a reference frequency which is
`
`
`
`
`
`
`
`not coherent with the most undesirable frequency of spuri-
`
`
`
`
`
`
`
`
`ous signals. This approach substantially eliminates interfer-
`
`
`
`
`
`
`
`cnce even though its frequency is likely to be initially
`
`
`
`
`
`
`
`
`
`unknown and may even change during operation.
`
`
`
`
`
`
`
`A position locator 18 processes the capacitance measure-
`
`
`
`
`
`
`
`ment signal from the synchronous electrode capacitance
`
`
`
`
`
`
`
`measurement unit 14 and provides position signals for use
`
`
`
`
`
`
`
`
`by a host computer, for example, and to the reference
`
`
`
`
`
`
`
`
`frequency generator 16. The position locator unit 18 deter-
`
`
`
`
`
`
`
`
`mines finger position signals based on the capacitance
`
`
`
`
`
`
`
`
`measurements. Several different systems are commonly
`
`
`
`
`
`
`known in the art for determining finger position based on
`
`
`
`
`
`
`
`
`measurements of capacitance associated with electrodes in
`
`
`
`
`
`an array. Position locators may provide one-dimensional
`
`
`
`
`
`
`
`sensing (such as for a volume slider control), two-dimen-
`
`
`
`
`
`
`
`sional sensing with contact determination (such as for com-
`
`
`
`
`
`
`
`
`puter cursor control), or full three-dimensional sensing (such
`
`
`
`
`
`
`
`as for games and three-dimensional computer graphics.) An
`
`
`
`
`
`
`
`example of a prior art position locator unit is shown in the
`
`
`
`
`
`
`
`
`Gerpheide ’Ol7 patent mentioned above, as units 40 and 50
`
`
`
`
`
`
`
`of FIG. 1 of the patent.
`
`
`
`
`
`
`Electrode Array
`
`
`FIG. 2A illustrates the electrodes in a preferred electrode
`
`
`
`
`
`
`array 12, together with a coordinate axes defining X and Y
`
`
`
`
`
`
`
`directions. One embodiment includes sixteen X electrodes
`
`
`
`
`
`
`and twelve Y electrodes, but for clarity of illustration, only
`
`
`
`
`
`
`
`
`
`six X electrodes 20 and four Y electrodes 22 are shown. It
`
`
`
`
`
`
`
`is apparent to one skilled in the art how to extend the number
`
`
`
`
`
`
`
`
`
`
`of electrodes. The array is preferably fabricated as a multi-
`
`
`
`
`
`
`
`layer printed circuit board 24. The electrodes are etched
`
`
`
`
`
`
`
`
`
`electrically conductive strips, connected to vias 26 which in
`
`
`
`
`
`
`turn connect them to other layers in the array. lllustratively,
`
`
`
`
`
`
`
`
`the array 12 is approximately 65 millimeters in the X
`
`
`
`
`
`
`
`
`direction and 49 millimeters in the Y direction. The X
`
`
`
`
`
`
`
`
`electrodes are approximately 0.7 millimeters wide on 3.3
`
`
`
`
`
`
`
`
`millimeter centers. The Y electrodes are approximately three
`
`
`
`
`
`
`
`millimeters wide on 3.3 millimeter centers.
`
`
`
`
`
`FIG. 2b illustrates the electrode array 12 from a side,
`
`
`
`
`
`
`
`
`
`cross-sectional view. An insulating overlay 21 is an approxi-
`
`
`
`
`
`mately 0.2 millimeters thick clear polycarbonate sheet with
`
`
`
`
`
`
`
`
`a texture on the top side which is comfortable to touch. Wear
`
`
`
`
`
`
`
`
`resistance may be enhanced by adding a textured clear hard
`
`
`
`
`
`
`
`coating over the top surface. The overlay bottom surface
`
`
`
`
`
`
`
`
`
`may be silk-screened with ink to provide graphics designs
`
`
`
`
`
`
`
`and colors.
`
`
`The X electrodes 20, Y electrodes 22, ground plane 25 and
`
`
`
`
`
`
`
`
`component
`traces 27 are etched copper traces within a
`
`
`
`
`
`
`
`
`multilayer printed circuit board. The ground plane 25 covers
`
`
`
`
`
`
`
`
`the entire array area and shields the electrodes from elec-
`
`
`
`
`
`
`
`
`
`
`
`Page 11 of 15
`
`

`
`
`
`6
`
`FIG. 4 shows one specific embodiment of a synchronous
`
`
`
`
`
`
`electrode capacitance measurement unit 14 connected to the
`
`
`
`
`
`
`electrode array 12,
`in which algebraic sums of mutual
`
`
`
`
`
`
`
`
`
`capacitances between electrodes are measured. The compo-
`
`
`
`
`
`
`
`nents are grouped into four main functional blocks. A virtual
`
`
`
`
`
`
`
`
`
`electrode synthesis block 70 connects each of the X elec-
`
`
`
`
`
`
`trodes to one of the wires CP or CN, and each of the Y
`
`
`
`
`
`
`
`
`
`
`electrodes to one of the wires RP or RN. The electrodes are
`
`
`
`
`
`
`
`
`selectively connected to the wires by switches , preferably
`
`
`
`
`
`
`CMOS switches under control of the position locator appa-
`
`
`
`
`
`
`
`
`ratus 18 (FIG. 1) to select appropriate electrodes for capaci-
`
`
`
`
`
`
`
`tance measurement. (See Gerpheide ’()l7 which describes
`
`
`
`
`
`
`
`such electrode selection by signal S of FIG. l of the patent.)
`
`
`
`
`
`
`
`
`All electrodes connected to the CP wire at any one time are
`
`
`
`
`
`
`
`
`
`considered to form a single “positive virtual X electrode”.
`
`
`
`
`
`
`Similarly, the electrodes connected to CN, RP, and RN form
`
`
`
`
`
`
`
`
`a “negative virtual X electrode”, a “positive virtual Y
`
`
`
`
`
`
`electrode”, and a “negative virtual Y electrode”, respec-
`
`
`
`
`
`
`tively.
`is preferably a digital
`The reference frequency signal
`
`
`
`
`
`
`logic signal from the reference frequency generator 16 (FIG.
`
`
`
`
`
`
`
`1). The reference frequency signal is supplied to unit 14 via
`
`
`
`
`
`
`
`
`an AND gate 72 also having a “drive enable” input, supplied
`
`
`
`
`
`
`
`
`by the reference frequency generator 16 (FIG. 1). The AND
`
`
`
`
`
`
`
`
`
`gate output feeds through inverter 74 and noninverting
`
`
`
`
`
`
`
`
`buffer 76 to wires RP and RN respectively which are part of
`
`
`
`
`
`
`a capacitive measurement element 78. In the preferred
`
`
`
`
`
`
`
`
`embodiment, the drive enable signal is always’ TRUE, to
`
`
`
`
`
`
`
`pass the reference frequency signal. In further preferred
`
`
`
`
`
`
`
`
`embodiments, it is asserted FALSE by the reference fre-
`
`
`
`
`
`
`
`queney generator when interference evaluation is to be
`
`
`
`
`
`
`
`
`performed as described later. When the drive enable signal
`
`
`
`
`
`
`
`is FALSE, the drive signal stays at a constant voltage level.
`
`
`
`
`
`
`
`
`When the drive signal is TRUE, it is a copy of the reference
`
`
`
`
`
`
`
`
`
`frequency signal.
`The capacitance measurement element 78 contains a
`
`
`
`
`
`
`differential charge transfer circuit 80 as illustrated in FIG. 4
`
`
`
`
`
`
`of Gerpheide, U.S. Pat. 5,349,303, incorporated herein by
`
`
`
`
`
`
`
`reference. Capacitors Csl and CS2 of FIG. 4 of that patent
`
`
`
`
`
`
`
`
`correspond to the stray capacitances of the positive and
`
`
`
`
`
`
`
`
`negative virtual electrodes to ground. The CHOP signal of
`
`
`
`
`
`
`
`
`that FIG. 4 is conveniently supplied in the present invention
`
`
`
`
`
`
`
`as a square wave signal having half the frequency of the
`
`
`
`
`
`
`
`
`
`
`reference frequency signal, as generated by the divide-by-2
`
`
`
`
`
`
`
`circuit 81 shown herein. As described in the Gerpheide ’303
`
`
`
`
`
`
`
`patent, the circuit maintains CP and CN (lines 68 and 72
`
`
`
`
`
`
`
`
`
`therein) at a constant virtual ground voltage.
`
`
`
`
`
`The capacitance measurement element 78 also contains a
`
`
`
`
`
`
`non-inverting drive buffer 76 which drives RN and negative
`
`
`
`
`
`
`virtual Y electrodes to change voltage levels copying the
`
`
`
`
`
`
`
`
`drive enable signal
`transitions. The inverting buffer 74
`
`
`
`
`
`
`
`
`drives RP and the positive virtual Y electrodes to change
`
`
`
`
`
`
`
`
`voltage levels opposite the drive enable signal transitions.
`
`
`
`
`
`
`
`
`Since CP and CN are maintained at virtual ground, these
`
`
`
`
`
`
`
`voltage changes are the net voltage changes across the
`
`
`
`
`
`
`
`
`
`mutual capacitances which exist between virtual Y and
`
`
`
`
`
`
`virtual X electrodes. Charges proportional to these voltage
`
`
`
`
`
`
`changes multiplied by the appropriate capacitance values are
`
`
`
`
`
`
`thereby coupled onto nodes CP and CN (the “coupled
`
`
`
`
`
`
`
`
`
`charges”). The charge transfer circuit therefore supplies a
`
`
`
`
`
`
`
`proportional differential charges at outputs Q01 and Q02,
`
`
`
`
`
`
`
`which are proportional to the coupled charges and thus to the
`
`
`
`
`
`
`
`
`capacitances.
`
`In short, this differential charge is a proportionality factor
`
`
`
`
`
`
`
`K times the “balance” L, which is a combination of these
`
`
`
`
`
`
`
`capacitances given by the equation-:
`
`
`
`
`
`
`
`5,565,658
`
`S
`
`trical interference which may be generated by the parts of
`
`
`
`
`
`
`
`
`the circuitry. The component traces 27 connect the vias 26
`
`
`
`
`
`
`
`
`
`and hence the electrodes 20, 22, to other circuit components
`
`
`
`
`
`
`
`
`
`of FIG. 1. Insulator 31, insulator 32 and insulator 33 are
`
`
`
`
`
`
`
`
`
`
`fiberglass-epoxy layers within the printed circuit board 24.
`
`
`
`
`
`
`
`
`They have respective thicknesses of approximately 1.0 n1il—
`
`
`
`
`
`
`
`limeter, 0.2 millimeters and 0.1 millimeters. Dimensions
`
`
`
`
`
`
`
`may be varied considerably as long as consistency is main-
`
`
`
`
`
`
`tained. However, all X electrodes 20 must be the same size,
`
`
`
`
`
`
`
`as must all Y electrodes 22.
`
`
`
`
`One skilled in the art will realize that a variety of
`
`
`
`
`
`
`
`
`
`
`techniques and materials can be used to form the electrode
`
`
`
`
`
`
`
`
`array. For example, FIG. 3A illustrates an alternative
`
`
`
`
`
`
`
`
`embodiment in which the electrode array includes an insu-
`
`
`
`
`
`
`
`lating overlay 40 as described above. Alternate layers of
`
`
`
`
`
`
`
`
`conductive ink 42 and insulating ink 43 are applied to the
`
`
`
`
`
`
`
`
`reverse surface by a silk screen process. The X electrodes 45
`
`
`
`
`
`
`
`are positioned between the insulating overlay 40 and X
`
`
`
`
`
`
`
`
`electrode conductive ink layer 42. Another insulating ink
`
`
`
`
`
`
`
`
`layer 43 is applied below layer 42. The Y electrodes 46 are
`
`
`
`
`
`
`
`
`positioned between insulating ink layer 43 and conductive
`
`
`
`
`
`
`
`ink layer 44. Another insulating ink layer 47 is applied
`
`
`
`
`
`
`
`
`
`below conductive ink layer 44, and ground plane 48 is
`
`
`
`
`
`
`
`
`
`affixed to Y electrode conductive ink layer 47. Each layer is
`
`
`
`
`
`
`
`
`approximately 0.01 millimeters thick.
`
`
`
`
`The resulting array is thin and flexible, which allows it to
`
`
`
`
`
`
`
`
`be formed into curved surfaces. In use it would be laid over
`
`
`
`
`
`
`
`
`
`a strong, solid support. In other examples,
`the electrode
`
`
`
`
`
`
`
`
`
`array may utilize a flexible printed circuit board, such as a
`
`
`
`
`
`
`
`
`flex circuit, or stampings of sheet metal or metal foil.
`
`
`
`
`
`
`
`
`A variety of electrode geometries and arrangements are
`
`
`
`
`
`
`
`
`possible for finger position sensing. One example is shown
`
`
`
`
`
`
`
`
`in FIG. 3b. This is an array of parallel electrode strips 50 for
`
`
`
`
`
`
`
`
`one-dimensional position sensing which could be useful as
`
`
`
`
`
`
`a “slider volume control” or “toaster darkness control”.
`
`
`
`
`
`
`
`Other examples include a grid of diamonds, or sectors of a
`
`
`
`
`
`
`disk.
`
`It is desired that the electrode array of the present inven-
`
`
`
`
`
`
`
`
`
`tion be easily fabricated by economical and widely available
`
`
`
`
`
`
`
`printed circuit board processes. It is also desired to allow use
`
`
`
`
`
`
`
`
`of various overlay materials selected for texture and low
`
`
`
`
`
`
`
`
`
`friction, upon which logo art work and coloration can be
`
`
`
`
`
`
`
`
`
`economically printed. A further preference is that the overlay
`
`
`
`
`
`
`
`may be custom printed separately from fabrication of the
`
`
`
`
`
`
`
`
`electrode-containing part of the array. This allows an eco-
`
`
`
`
`
`
`
`
`nomical standardized mass production of that part of the
`
`
`
`
`
`
`
`
`
`array, and later affixing of the custom printed overlay.
`
`
`
`
`
`
`
`
`
`Synchronous Electrode Capacitance Measurement
`
`
`
`
`FIG. 4 shows one embodiment of the synchronous elec-
`
`
`
`
`
`
`
`trode capacitance measurement unit 14 in more detail. The
`
`
`
`
`
`
`
`key elements of the synchronous electrode capacitance
`
`
`
`
`
`
`
`measurement unit 14 are (a) an element for producing a
`
`
`
`
`
`
`
`
`
`voltage change in the electrode array synchronously with a
`
`
`
`
`
`
`
`reference signal, (b) an element producing a signal indica-
`
`
`
`
`
`
`
`
`tive of the displacement charge thereby coupled between
`
`
`
`
`
`
`
`
`electrodes of the electrode array, (c) an element for demodu-
`
`
`
`
`
`
`
`
`lating this signal synchronously with the reference signal,
`
`
`
`
`
`
`
`
`and (d) an element for low pass filtering the demodulated
`
`
`
`
`
`
`
`
`
`
`signal. Unit 14 is coupled to the electrode array, preferably
`
`
`
`
`
`
`
`through a multiplexer or switches. The capacitances to be
`
`
`
`
`
`
`measured in this embodiment are mutual capacitances
`
`
`
`
`
`
`between electrodes but could be stray capacitances of elec-
`
`
`
`
`
`
`
`trodes to ground or algebraic sums (that is sums and differ-
`
`
`
`
`
`
`
`
`ences) of such mutual or stray ca