United States Patent [19]
`Bisset et al.
`
`USOO5543588A
`[11] Patent Number:
`[451 Date of Patent:
`
`5,543,588
`Aug. 6, 1996
`
`[54]
`
`TOUCH PAD DRIVEN HANDHELD
`COMPUTING DEVICE
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`[75]
`
`Inventors: Stephen Bisset, Palo Alto; Robert J.
`Miller, Fremont; Timothy P. Allen, Los
`Gatos; Giinter Steinbach, Palo Alto, all
`of Calif.
`
`[73]
`
`Assignec: Synaptics, Incorporated, San Jose,
`Calif.
`
`[211
`[22]
`
`Appl. No.: 161,671
`Filed:
`Dec. 3, 1993
`
`(Under 37 CFR 1.47)
`
`Related U.S. Application Data
`
`[63]
`
`[51]
`[52]
`[53]
`
`Continuation-impart of Scr. No. 895,934, Jun, 8, 1992, and
`a continuation-in-part of Ser, No. 115,743, Aug. 31, 1993,
`Pat. No. 5,374,787.
`
`Int. Cl.6 ........................... .. G08C 21/00; G096 5/00
`
`................... .. 178/18; 345/173
`Field of Search ........................ .. 178/18, 19; 341/33,
`341/34; 345/173, 174
`
`5,327,163
`
`7/1994 Hashimoto et al. ................ .. 178/18 X
`
`FOREIGN PATENT DOCUMENTS
`
`2662528 11/1991 European Pat. 01f. .
`Primary Examiner—Stephen Chin
`Assistant Examiner-Kevin Kim
`Attorney, Agent, or Firm—D’Alessandro & Ritchie
`
`[57]
`
`ABSTRACT
`
`A handheld computing device comprises a thin enclosure
`having two opposing major faces. A display screen is
`disposed on a ?rst one of the major opposing faces of the
`enclosure and a touch-sensitive object position detector
`input device is disposed on a second one of the major
`opposing faces of the enclosure. Computing device circuitry,
`circuitry for interfacing the touch-sensitive object position
`detector to the computing device circuitry, and circuitry for
`driving the display screen are all disposed within the enclo
`sure.
`
`4 Claims, 15 Drawing Sheets
`
`SCEA Ex. 1018 Page 1
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`

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`US. Patent
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`Aug. 6, 1996
`
`Sheet 1 of 15
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`5,543,588
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`12
`
`FIG. 1B
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`SCEA Ex. 1018 Page 2
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`

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`U.S. Patent
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`Aug. 6, 1996
`
`Sheet 2 0f 15
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`5,543,588
`
`FIG. 1C
`
`24
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`SCEA Ex. 1018 Page 3
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`

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`US. Patent
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`Aug. 6, 1996
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`SCEA Ex. 1018 Page 4
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`SCEA Ex. 1018 Page 4
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`

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`US. Patent
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`Aug. 6, 1996
`
`Sheet 4 of 15
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`5,543,588
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`SCEA EX. 1018 Page 5
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`SCEA Ex. 1018 Page 5
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`

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`US. Patent
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`Aug. 6, 1996
`
`Sheet 5 of 15
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`5,543,588
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`SCEA Ex. 1018 Page 6
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`

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`US. Patent
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`Aug. 6, 1996
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`Sheet 6 of 15
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`5,543,588
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`SCEA EX. 1018 Page 7
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`SCEA Ex. 1018 Page 7
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`

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`US. Patent
`
`Aug. 6, 1996
`
`Sheet 7 of 15
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`5,543,588
`
`NODE
`FIG. 6C
`
`SCEA Ex. 1018 Page 8
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`

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`US. Patent
`
`Aug. 6, 1996
`
`Sheet 8 of 15
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`SCEA Ex. 1018 Page 9
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`SCEA Ex. 1018 Page 9
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`

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`US. Patent
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`Aug. 6, 1996
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`Sheet 9 of 15
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`5,543,588
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`SCEA EX. 1018 Page 10
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`SCEA Ex. 1018 Page 10
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`

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`U.S. Patent
`
`Aug. 6, 1996
`
`Sheet 10 of 15
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`5,543,588
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`
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`SCEA EX. 1018 Page 11
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`SCEA Ex. 1018 Page 11
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`

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`US. Patent
`
`Aug. 6, 1996
`
`Sheet 11 0f 15
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`SCEA Ex. 1018 Page 12
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`

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`US. Patent
`
`Aug. 6, 1996
`
`Sheet 12 of 15
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`5,543,588
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`SCEA Ex. 1018 Page 13
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`

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`US. Patent
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`Aug. 6, 1996
`
`Sheet 13 of 15
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`5,543,588
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`SCEA Ex. 1018 Page 14
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`

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`US. Patent
`
`Aug. 6, 1996
`
`Sheet 14 0f 15
`
`5,543,588
`
`314
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`SCEA Ex. 1018 Page 15
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`

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`U.S. Patent
`
`Aug. 6, 1996
`
`Sheet 15 of 15
`
`5,543,588
`
`r‘ 320
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`SCEA Ex. 1018 Page 16
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`

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`5,543,588
`
`1
`TOUCH PAD DRIVEN HANDHELD
`COMPUTING DEVICE
`
`RELATED APPLICATIONS
`
`This application is a continuation-in—part of application
`Ser. No. 07/895,934, ?led Jun. 8, 1992, and of application
`Scr. No. 08/115,743, ?led Aug. 31, 1993, now U.S. Pat. No.
`5,374,787 entitled OBJECT POSITION DETECTOR.
`
`BACKGROUND OF THE INVENTION
`
`2
`reliably when the ?nger carries electrical noise, or when the
`touch surface is contaminated with dirt or moisture.
`Because of the drawbacks of resistive devices, many
`attempts have been made to provide pointing capability
`based on capacitively sensing the position of the ?nger. U.S.
`Pat. No. 3,921,166 to Volpe teaches a capacitive matrix in
`which the ?nger changes the transcapacitance between row
`and column electrodes. U.S. Pat. No. 4,103,252 to Bobick
`employs four oscillating signals to interpolate x and y
`positions between four capacitive electrodes. U.S. Pat. No.
`4,455,452 to Schuyler teaches a capacitive tablet wherein
`the ?nger attenuates the capacitive coupling between elec
`trodes.
`U.S. Pat. No. 4,550,221 to Mabusth teaches a capacitive
`tablet wherein the elfective capacitance to “virtual ground”
`is measured by an oscillating signal. Each row or column is
`polled sequentially, and a rudimentary form of interpolation
`is applied to resolve the position between two rows or
`columns. An attempt is made to address the problem of
`electrical interference by averaging over many cycles of the
`oscillating waveform. The problem of contamination is
`addressed by sensing when no ?nger was present, and
`applying a periodic calibration during such no-?nger~present
`periods. U.S. Pat. No. 4,639,720 to Rympalski teaches a
`tablet for sensing the position of a stylus. The stylus alters
`the transcapacitance coupling between row and column
`electrodes, which are scanned sequentially. U.S. Pat. No.
`4,736,191 to Matzke teaches a radial electrode arrangement
`under the space bar of a keyboard, to be activated by
`touching with a thumb. This patent teaches the use of total
`touch capacitance, as an indication of the touch pressure, to
`control the velocity of cursor motion. Pulsed sequential
`polling is employed to address the effects of electrical
`interference.
`U.S. Pat. Nos. 4,686,332 and 5,149,919, to Greanias,
`teaches a stylus and ?nger detection system meant to be
`mounted on a CRT. As a ?nger detection system, its X/Y
`sensor matrix is used to locate the two matrix wires carrying
`the maximum signal. With a coding scheme these two wires
`uniquely determine the location of the ?nger position to the
`resolution of the wire stepping. For stylus detection, Gre
`anias ?rst coarsely locates it, then develops a virtual dipole
`by driving all lines on one side of the object in one direction
`and all lines on the opposite side in the opposite direction.
`This is done three times with different dipole phases and
`signal polarities. Assuming a predetermined matrix response
`to the object, the three measurements ‘present a set of
`simultaneous equations that can be solved for position.
`U.S. Pat. No. 4,733,222 to Evans is the ?rst to teach a
`capacitance touch measurement system that interpolates to a
`high degree. Evans teaches a three terminal measurement
`system that uses a drive, sense and electrode signal set (3
`signals) in its matrix, and bases the measurement on the
`attenuation effect of a ?nger on the electrode node signal
`(uses a capacitive divider phenomena). Evans sequentially
`scans through each drive set to measure the capacitance.
`From the three largest responses an interpolation routine is
`applied to determine ?nger position. Evans also teaches a
`zeroing technique that allows “no~?nger” levels to be can»
`celled out as part of the measurement.
`U.S. Pat. No. 5,016,008 to Gruaz describes a touch
`sensitive pad that also uses interpolation. Gruaz uses a drive
`and sense signal set (2 signals) in the touch matrix and like
`Evans relies on the attenuation e?’ect of a ?nger to modulate
`the drive signal. The touch matrix is sequentially scanned to
`read each matrix lines response. An interpolation program
`
`1. Field of the Invention
`The present invention relates to handheld computing
`devices such as personal digital assistants, pocket calendars,
`communicators, home remote control units and calculators.
`In particular, the present invention relates to computing
`devices that are meant to be very compact and possibly
`carried in a pocket or purse and which employ touch sensing
`technology as the major means of data input. Personal digital
`assistants are computing devices that will include all of these
`areas and maintain personal schedulers, telephone books,
`etc.
`2. The Prior Art
`There are several available touch-sense technologies
`which may be employed for use as a position indicator.
`Resistive~membranc position sensors are known and used in
`several applications. However, they generally suffer from
`poor resolution, the sensor surface is exposed to the user and
`is thus subject to wear. In addition, resistive—membrane
`touch sensors are relatively expensive. A one-surface
`approach requires a user to be grounded to the sensor for ‘
`reliable operation. This cannot be guaranteed in portable
`computers. An example of a one~surfacc approach is the
`UnMouse product by MicroTouch, of Wilmington, Mass. A
`two-surface approach has poorer resolution and potentially
`will wear out very quickly in time.
`Resistive tablets are taught by U.S. Pat. No. 4,680,430 to
`Yoshikawa, U.S. Pat. No. 3,497,617 to Ellis and many
`others. The drawback of all such approaches is the high
`power consumption and the high cost of the resistive mem
`brane employed.
`Surface Acoustic Wave (SAW) devices have potential use
`as position indicators. However, this sensor technology is
`expensive and is not sensitive to light touch. In addition,
`SAW devices are sensitive to residue buildup on the touch
`surfaces and generally have poor resolution.
`Strain gauge or pressure plate approaches are an interest
`ing position sensing technology, but suffer from several
`drawbacks. This approach may employ piezoelectric trans
`ducers. One drawback is that the piezo phenomena is an AC
`phenomena and may be sensitive to the user’s rate of
`movement. In addition, strain gauge or pressure plate
`approaches are a somewhat expensive because special sen
`sors are required.
`Optical approaches are also possible but are somewhat
`limited for several reasons. All would require light genera
`tion which will require external components and increase
`cost and power drain. For example, a “?nger-breaking”
`infra-red matrix position detector consumes high power and
`suffers from relatively poor resolution.
`There have been numerous attempts to provide a device
`for sensing the position of thumb or other ?nger for use as
`a pointing device to replace a mouse or trackball. Desirable
`attributes of such a device are low power, low pro?le, high
`resolution, low cost, fast response, and ability to operate
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`3
`then selects the two largest adjacent signals in both dimen
`sions to determine the ?nger location, and ratiometrically
`determines the effective position from those 4 numbers. '
`Gerpheide, PCT application U.S. Ser. No. 90/04584,
`publication No. WO9l/03039, applies to a touch pad system
`a variation of the virtual dipole approach of Greanias.
`Gerpheide teaches the application of an oscillating potential
`of a given frequency and phase to all electrodes on one side
`of the virtual dipole, and an oscillating potential of the same
`frequency and opposite phase to those on the other side.
`Electronic circuits develop a “balance signal” which is Zero
`when no ?nger is present, and which has one polarity if a
`?nger is on one side of the center of the virtual dipole, and
`the opposite polarity if the ?nger is on the opposite side. To
`acquire the position of the ?nger initially, the virtual dipole
`is scanned sequentially across the tablet. Once the ?nger is
`located, it is “tracked” by moving the virtual dipole toward
`the ?nger once the ?nger has moved more than one row or
`column.
`Because the virtual dipole method operates by generating
`a balance signal that is zero when the capacitance does not
`vary with distance, it only senses the perimeter of the ?nger
`contact area, rather than the entire contact area. Because the
`method relies on synchronous detection of the exciting
`signal, it must average for long periods to reject electrical
`interference, and hence it is slow. The averaging time
`required by this method, together with the necessity to
`search sequentially for a new ?nger contact once a previous
`contact is lost, makes this method, like those before it, fall
`short of the requirements for a fast pointing device that is not
`affected by electrical interference.
`It should also be noted that all previous touch pad
`inventions that used interpolation placed rigorous design
`requirements on their sensing pad. Greanias and Evans use
`a complicated and expensive drive, sense and electrode line
`scheme to develop their signal. Gruaz and Gerpheide use a
`two signal drive and sense set. In the present invention the
`driving and sensing is done on the same line. This allows the
`row and column sections to be symmetric and equivalent.
`This in turn allows independent calibration of all signal
`paths, which makes board layout simpler and less constrain~
`ing, and allows for more unique sensor topologies.
`The shortcomings of the inventions and techniques
`described in the prior art can also be traced to the use of only
`one set of driving and sensing electronics, which was
`multiplexed sequentially over the electrodes in the tablet.
`This arrangement was cost effective in the days of discrete
`components, and avoided offset and scale differences among
`circuits.
`The sequential scanning approach of previous systems
`also made them more susceptible to noise. Noise levels
`could change between successive measurements, thus
`changing the measured signal and the assumptions used in
`interpolation routines.
`Finally, all previous approaches assumed a particular
`signal response for ?nger position versus matrix position.
`Because the transfer curve is very sensitive to many param
`eters and is not a smooth linear curve as Greanias and
`Gerpheide assume, such approaches are limited in the
`amount of interpolation they can perform.
`The touch sensing technology of the present invention
`may be particularly useful when employed as an input
`transducer for a handheld computing device. Numerous
`handheld computing devices such as personal digital assis
`tants have been appearing on the market, Examples are
`Sharp’s Wizard, Apple’s Newton and similar Hewlett Pack
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`ard products. Presently most of these devices use either a
`miniature keypad input or some type of stylus on top of an
`LCD display.
`In all cases the market push is for smaller and more
`compact systems that eventually ?t easily into ones pocket
`or purse. High levels of integration have driven down the
`size of computing devices to the level where a reasonably
`powerful computing device can ?t in the volume of a credit
`card. One of the signi?cant obstacles in reducing the size of
`such computing devices has been the size of the user input
`interface. A keypad input or stylus/?nger on top of an LCD
`display, which is the industry-standard input paradigm, is
`currently a limiting factor.
`As will be appreciated by those of ordinary skill in the art,
`keypads obviously have a certain minimum size below
`which they are no longer useful. The input regime wherein
`a stylus/?nger is moved across the surface of an LCD
`display will suffer from interference of view. Because the
`display screens must necessarily be small, the presence of a
`stylus or ?nger writing on the screen tends to block the
`user’s view of a large portion of the screen.
`It is thus an object of the present invention to provide a
`two-dimensional capacitive sensing system equipped with a
`separate set of drive/sense electronics for each row and for
`each column of a capacitive tablet, wherein all row elec
`trodes are sensed simultaneously, and all column electrodes
`are sensed simultaneously.
`It is a further object of the present invention to provide an
`electronic system that is sensitive to the entire area of
`contact of a ?nger with a capacitive tablet, and to provide as
`output the coordinates of some measure of the center of this
`contact area while remaining insensitive to the characteristic
`pro?le of the object being detected.
`It is a further object of the present invention to provide an
`electronic system that provides as output some measure of
`area of contact of a ?nger with a capacitive tablet.
`Yet another object of the present invention to provide a
`handheld computing device where almost the entire surface
`area of one face of the device can be used as a display and
`where the main means for data entry by a user is disposed
`on a second face of the device.
`Yet another object of this invention to provide a low-cost,
`low-parts-count input transducer for a handheld computing
`device using a touch pad technology such as the one
`described in co-pending application Ser. Nos. 07/895,934
`and 08/115,743, now US. Pat. No. 5,734,787.
`
`BRIEF DESCRIPTION OF THE INVENTION
`
`With the advent of very high levels of integration, it has
`become possible to integrate many channels of driving/
`sensing electronics into one integrated circuit, along with the
`control logic for operating them, and the interface electron
`ics to allow the pointing device to communicate directly
`with a host microprocessor. The present invention uses
`adaptive analog techniques to overcome offset and scale
`differences between channels, and can thus sense either
`transcapacitance or self-capacitance of all tablet rows or
`columns in parallel. This parallel-sensing capability, made
`possible by providing one set of electronics per row or
`column, allows the sensing cycle to be extremely short, thus
`allowing fast response while still maintaining immunity to
`very high levels of electrical interference.
`The present invention comprises a position-sensing tech
`nology particularly useful for applications where ?nger
`position information is needed, such as in computer
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`SCEA Ex. 1018 Page 18
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`“mouse” or trackball environments. However the position
`sensing technology of the present invention has much more
`general application than a computer mouse, because its
`sensor can detect and report if one or more points are being
`touched. In addition, the detector can sense the pressure of
`the touch.
`According to a preferred embodiment of the present
`invention, referred to herein as a “?nger pointer” embodi~
`ment, a position sensing system includes a position sensing
`transducer comprising a touch-sensitive surface disposed on
`a substrate, such as a printed circuit board, including a
`matrix of conductive lines. A ?rst set of conductive lines
`runs in a ?rst direction and is insulated from a second set of
`conductive lines running in a second direction generally
`perpendicular to the ?rst direction. An insulating layer is
`disposed over the ?rst and second sets of conductive lines.
`The insulating layer is thin enough to promote signi?cant
`capacitive coupling between a ?nger placed on its surface
`and the ?rst and second sets of conductive lines.
`Sensing electronics respond to the proximity of a ?nger to
`translate the capacitance changes of the conductors caused
`by ?nger proximity into position and touch pressure infor
`mation. Its output is a simple X, Y and pressure value of the
`one object on its surface.
`Different prior art pad scan techniques have different
`advantages in different environments. Parallel drive/sense
`techniques according to the present invention allow input
`samples to be taken simultaneously, thus all channels are
`affected by the same phase of an interfering electrical signal,
`greatly simplifying the signal processing and noise ?ltering.
`There are two drive/sense methods employed in the touch
`sensing technology of the present invention. According to a
`?rst and presently preferred embodiment of the invention,
`the voltages on all of the X lines of the sensor matrix are
`simultaneously moved, while the voltages of the Y lines are
`held at a constant voltage, with the complete set of sampled
`points simultaneously giving a pro?le of the ?nger in the X
`dimension. Next, the voltages on all of the Y lines of the
`sensor matrix are simultaneously moved, while the voltages
`of the X lines are held at a constant voltage to obtain
`complete set of sampled points simultaneously giving a
`pro?le of the ?nger in the other dimension.
`According to a second drive/sense method, the voltages
`on all of the X lines of the sensor matrix are simultaneously
`moved in a positive direction, while the voltages of the Y
`lines are moved in a negative direction. Next, the voltages on
`all of the X lines of the sensor matrix are simultaneously
`moved in a negative direction, while the voltages of the Y
`lines are moved in a positive direction. This technique
`doubles the effect of any transcapacitance between the two
`dimensions, or conversely, halves the effect of any parasitic
`capacitance to ground. In both methods, the capacitive
`information from the sensing process provides a pro?le of
`the proximity of the ?nger to the sensor in each dimension.
`Both embodiments then take these pro?les and calculate
`the centroid for X and Y position and integrate under the
`curve for the Z pressure information. The position sensor of
`these embodiments can only report the position of one object
`on its sensor surface. If more than one object is present, the
`position sensor of this embodiment computes the centroid
`position of the combined set of objects. However, unlike
`prior art, because the entire pad is being pro?led, enough
`information is available to discern simple multi-?nger ges
`tures to allow for a more powerful user interface.
`According to another aspect of the present invention,
`several power reduction techniques which can shut down the
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`circuit between measurements have been integrated into the
`system. This is possible because the parallel measurement
`technique according to the present invention is so much
`faster than prior art techniques.
`According to a further aspect of the invention, noise
`reduction techniques that are focused on reducing noise
`produced in typical computer environments are integrated
`into the system.
`According to yet another aspect of the present invention,
`a capacitance measurement technique which is easier to
`calibrate and implement is employed.
`A handheld computing device according to the present
`invention may be packaged in a small enclosure wherein a
`display is disposed on a ?rst face of the device and a touch
`pad input device is disposed on a second face of the device.
`The touch pad input device is mapped one-to-one into the
`display on the front side of the module. Computing circuitry
`is contained in the enclosure and coupled to the visual
`display and to the touch panel. The computing circuitry
`accepts input information from the touch panel and displays
`visual information developed from the input information on
`the visual display.
`The present invention uses the very dense touch pad input
`technology disclosed herein in a novel way to make the
`development of a credit card size handheld computing
`device practical. The space layout efficiency of this touch
`pad technology results from the use of printed circuit board
`traces as sensors and thereby doesn’t require a special
`transducer. The present invention takes advantage of this by
`providing a novel arrangement whereby the input sensor is
`mounted on a face of the device opposite to the face upon
`which the display is disposed. By so positioning these
`elements of the invention, there is no interference between
`the display and the input touch pad, and the device may be
`con?gured in a minimum sized enclosure.
`As a non-limiting illustration of a presently preferred
`embodiment of the invention, the handheld computing
`device of the present invention may, for example, take the
`form of a personal digital assistant. Such devices are known
`in the art and are used for such purposes as tracking personal
`schedules, maintaining a personal calendar and/or notepad,
`and providing a calculator. The output is displayed on an
`LCD display and may be organized in a menu driven
`fashion. For alphanumeric input a small keyboard would be
`displayed from which the user would select the characters
`needed by touching appropriate areas on the touchpad on the
`underside of the enclosure.
`To use the device, the user would hold the unit in one hand
`(left hand for example/while sliding the index ?nger of the
`right hand under the display to select the items of interest.
`The left hand would also be used to operate a select switch
`on the upper or lower edge of the module, to allow for the
`click and select or click and drag idioms employed in mouse
`input to computers.
`The bene?ts of the handheld computing device of the
`present invention are that it permits direct one~to~one control
`of cursor position, allows almost the full surface to be used
`for the display, and employs very inexpensive input tech
`nology. In addition, the ?nger or stylus does not obscure the
`view of the display, the ?nger can stay in contact with the
`cursor so that the cursor position is not lost, and a keyboard
`can be displayed for alphanumeric input.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1a is a top view of an object position sensor
`transducer according to a presently preferred embodiment of
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`the invention showing the object position sensor surface
`layer including a top conductive trace layer and conductive
`pads connected to a bottom trace layer. FIG. 1b is a bottom
`view of the object position sensor transducer of FIG. 1a
`showing the bottom conductive trace layer. FIG. 1c is a
`composite view of the object position sensor transducer of
`FIGS. 1a and 1b showing both the top and bottom conduc
`tive trace layers.
`FIG. 1d is a cross-sectional view of the object position
`sensor transducer of FIGS. 1a—1c.
`FIG. 2 is a block diagram of sensor decoding electronics
`which may be used with the sensor transducer in accordance
`with a preferred embodiment of the present invention.
`FIG. 3a is a simpli?ed schematic diagram of a charge
`integrator circuit which may be used in the present inven
`tion.
`FIG. 3b is a schematic diagram of an illustrative sche
`matic diagram of the charge integrator circuit of FIG. 3a.
`FIG. 4 is a timing of the operation of charge integrator
`circuit of FIGS. 3a and 3b.
`FIG. 5 is a schematic diagram of an illustrative ?lter and
`sample/hold circuit for use in the present invention.
`FIG. 6a is a schematic diagram of an illustrative minimum
`selector and subtractor circuit including peak rejection
`which may be employed in the present invention, showing
`circuit details of four individual channels and their inter
`connection.
`FIG. 6b is a representation of what the output of the
`minimum selector and subtractor circuit of FIG. 6a would be
`like without the background level removed.
`FIG. 60 is a representation of the output of the minimum
`selector and subtractor circuit of FIG. 6a with the back
`ground level removed.
`FIG. 7 is a schematic diagram of an illustrative OTA
`circuit used in the minimum selector and subtractor circuit,
`showing how the outputs Pout and Zout are derived, and
`further showing a current sink and source options, Poutn and
`Poutp, respectively, for the Pout output.
`FIG. 8 is a schematic diagram of an illustrative maximum
`detector circuit which may be used in the present invention.
`FIG. 9a is a schematic diagram of an illustrative position
`encoder circuit which may be used in the present invention.
`FIG. 9b is a schematic diagram of an P-type OTA circuit
`which may be used in the position encoder circuit of the
`present invention.
`FIG. 90 is a schematic diagram of an N‘type OTA circuit
`which may be used in the position encoder circuit of the
`present invention.
`FIG. 10 is a schematic diagram of an illustrative ZSum
`circuit which may be used in the present invention.
`FIG. 11 is a users view of the handheld computing device
`of the present invention.
`FIG. 12 is a view of the back side of the handheld
`computing device of the present invention showing the
`touch pad area which would be positioned directly opposite
`the display.
`FIG. 13 is an illustrative block diagram of a handheld
`computing device according to the present invention.
`FIG. 14 shows the internal physical layout of an illustra
`tive system printed circuit board from a top view.
`FIG. 15 shows a bottom view of the internal physical
`layout of the system printed circuit board of FIG. 4.
`FIG. 16 is a cross-sectional view of the handheld com
`puting device of the present invention viewed from the
`bottom of the module.
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`FIG. 17 is a three dimensional rendering showing how a
`typical user might handle the handheld computing device of
`the present invention.
`
`DETAILED DESCRIPTION OF A PREFERRED
`EMBODIMENT
`
`Those of ordinary skill in the art will realize that the
`following description of the present invention is illustrative
`only and not in any way limiting. Other embodiments of the
`invention will readily suggest themselves to such skilled
`persons.
`The present invention brings together in combination a
`number of unique features which allow for new applications
`not before possible. Because the object position sensor of the
`present invention has very low power requirements, it is
`bene?cial for use in battery operated or low power applica
`tions such as lap top or portable computers. It is also a very
`low cost solution, has no moving parts (and is therefore
`virtually maintenance free), and uses the existing printed
`circuit board traces for sensors. The sensing technology of
`the present invention can be integrated into a computer
`motherboard to even further lower its cost in computer
`applications. Similarly, in other applications the sensor can
`be part of an already existent circuit board.
`Because of its small size and low pro?le, the sensor
`technology of the present invention is useful in lap top or
`portable applications where volume is important consider
`ation. The sensor technology of the present invention
`requires circuit board space for only a single sensor interface
`chip that can interface directly to a microprocessor, plus the
`area needed on the printed circuit board for sensing.
`The sensor material can be anything that allows creation
`of a conductive X/Y matrix of pads. This includes not only
`standard PC board, but also ?exible PC board, conductive
`elastomer materials, silk-screened conductive lines, and
`piezo-electric Kynar plastic materials. This renders it useful
`as well in any portable equipment application or in human
`interface where the sensor needs to be molded to ?t within
`the hand.
`The sensor can be conformed to any three dimensional
`surface. Copper can be plated in two layers on most any
`surface contour producing the sensor. This will allow the
`sensor to be adapted to the best ergonomic form needed for
`a application. This coupled with the “light-touch” feature
`will make it effortless to use in many applications. The
`sensor can also be used in an indirect manner, i.e it can have
`a conductive foam over the surface and be used to detect any
`object (not just conductiv