United States Patent
`Caldwell et al.
`
`115
`
`MANUINAAA
`(11) Patent Number:
`5,189,417
`[45] Date of Patent:
`Feb. 23, 1993
`
`364/862
`3/1979
`4,145,748
`5/1979
`4,152,629
`ws 315/362
`
`4,159,473 6/1979
`ww 340/565
`
`4,161,766
`7/1979 Castleberryetal.
`.. 361/280
`
`4,174,517 11/1979 Mandel............
`340/310 B
`
`wn 307/116
`4,210,822 7/1980 WEED csscsseceeeee
`
`4.211.959 7/1980 Deavenport et al.
`«315/362
`
`7/1980 Conmer.......-.-
`4,213,061
`307/116
`.. 178/18
`4,220,815
`9/1980 Gibson etal.
`
`9/1980 Grimes etal.
`4,223,301
`340/500
`
`4,237,386 12/1980 Instance...
`we 307/116
`
`307/252 H
`4,264,831
`4/1981 Wern.
`
`9/1981 Wern ........
`wi307/116
`4,289,972
`
`4,289,980 9/1981 McLaughlin ....
`307/308
`9/1981 Eichelberger etal. .
`.. 340/33
`4,290,052
`
`9/1981 Cutler et al. or
`yasae
`4,291,303
`
`es
`4,293,987 10/1981 Gottbrechtet al.
`42
`.. 219/10.55 B
`4,304,976 12/1981 Gottbrechtetal.
`(List continued on next page.)
`
`Primary Examiner—Donald J. Yusko
`2/1957 Rug ...ereccccrceereeererees
`2,782,308
`Assistant Examiner-—Michael Horabik
`«331/65
`
`3,040,178 6/1962 Lyman etal.
`a Attorney, Agent, or Firm—Price, Heneveid, Cooper,
`
`3,200,304
`
`8/1965 Atkins et al. ...
`” 361/179
`Dewitt & Litton
`3,200,305
`8/1965 Atkinsetal....
`
`3,200,306
`8/1965 Atkins et al.
`...
`
`ABSTRACT
`“331
`(£57)
`3,254,313 5/1966 Atkinsetal.
`
`3,275,897 9/1966 Atkinsetal.
`
`A circuit for detecting user contact of one of a plurality
`3,549,909 12/1970 Adelson.....
`
`” 318/345
`of touch pads includes a plurality of drive lines and a
`3,641,410 2/1972 Vogelsberg
`
`” 318/446
`plurality of sense lines coupled with the touch pads. A
`3,651,391
`3/1972 Vogelsberg
`. 315/208
`sense Circuit responsive to the signals on the sense lines
`
`3,666,988
`5/1972 Bellis......
`_ 178/18
`produces a pulse having a width that is proportional to
`3,798,370
`3/1974 Hurst ..
`
`. 341/33
`the amplitude of each of the sense signals. A control
`3,846,791 11/1974 Foster....
`
`. 315/34
`circuit measures the width of the pulses produced by
`3,899,713
`8/1975 Barkan et al
`
`- 178/18
`the sense circuit and compares each measured pulse
`3,911,215 10/1975 Hurst etal.
`
`a 050 width to a reference pulse width to distinguish between
`3,965,465
`6/1976 Alexander..
`
`3,984,757 10/1976 Gott et al.
`..
`aan315“43
`a touch and no-touch condition for each touch pad. The
`
`4,016,453 4/1977 Moennig....
`
`“307/116
`sense circuit is illustrated in the form of a comparator
`4,031,408
`6/1977 Holz.......
`.. 200/5 A
`having a threshold inputthat is always exceeded by the
`4,056,699 11/1977 Jordan .......
`
`sees 178/18
`sense signal to producethe variable width pulse. Sepa-
`4,071,689
`1/1978 Talmageetal.
`
`aia
`rate amplifiers may be provided for each senseline.
`4,090,092
`5/1978 Serrano.....
`
`4,101,805
`7/1978 Stone ......
`340/531
`4,101,886
`7/1978 Grimesetal.
`
`. 307/116
`4,119,864 10/1978 Petrizio ..
`. 200/52 R
`
`4,123,631 10/1978 Lewis.....
`sesesneeeee 307/308
`4,136,291
`1/1979 Waldron...........
`
`24 Claims, 5 Drawing Sheets
`
`APPLE 1018
`
` 1
`
`[54] DETECTION CIRCUIT FOR MATRIX
`TOUCH PAD
`Inventors: David W. Caldwell; Nicholas W.
`Medendorp, both of Holland, Mich.
`.
`.
`[73] Assignee: Donnelly Corporation, Holland,
`Mich.
`.
`[21] Appl. No.: 598,129
`[22] Filed:
`Oct. 16, 1990
`[ST]
`int, C15eeesseessssesssessessersssessneceneeess H03M 11/20
`[52] US. Ch, ceesceceeceseenssnessnsencesceeecretee 341/26; 341/34;
`364/189
`{58] Field of Search.............0-:0 341/33, 34, 26, 22,
`.
`.
`.
`.
`341/24; 200/600; 400/479.1; 364/189; 379/368
`References Cited
`U.S. PATENT DOCUMENTS
`
`[75]
`
`[56]
`
`1
`
`APPLE 1018
`
`

`

`5,189,417
`ee,
`U.S. PATENT DOCUMENTS
`4,535,254
`8/1985 Khatri ......
`we 307/38
`
`
`4,550,310 10/1985 Yamaguchietal.
`. 341/33
`4,323,829 4/1982 Witney et al. uueeeeeeens 318/55
`4,561,002 12/1985 ChUi «cere
`. 341/26
`
`
`4,360,737 11/1982 Leopold ....ccsesessesesseeereesseee: 307/116
`1/1986 Yoshikawaetal.
`4,567,470
`. 341/33
`
`.. 340/711
`4,584,519 4/1986 Groudis ween
`4,374,381
`2/1983 Neg etal.
`1 323/245
`
`4,380,040 4/1983 Posset......
`9/1986 POUjois ....ssececsssesssssesesecennsees 341/33
`361/290
`4,614,937
`
`
`7/1983 Williams.....
`. 341/33
`4,394,643
`4,651,133
`3/1987 Ganesan etal.
`we 341/33
`
`.. 361/290
`8/1983 Frame.....
`4,709,228 11/1987 Huckingetal.
`341/26 X
`4,400,758
`
`9/1983 Chai ........
`. 341/26
`3/1988 Grabneretal.
`... 361/280
`4,405,917
`4,731,694
`
`9/1983 Wall etal...
`. 341/26
`.......sssceecerncrceeerrees 341/22
`4,405,918
`4,736,190 4/1988 Fiorella
`
`4,413,252 11/1983 Tyler etal. ....
`. 341/33
`4/1988 Brown.....
`oe 340/712
`4,740,781
`
`3/1984 Calandrello et al.
`.....
`200/519
`5/1988 Alexander...
`. 340/712
`4,439,647
`4,743,895
`
`............
`340/712
`8/1989 Schultz, Jr.
`.. 200/600
`4,476,463 10/1984 Negetal.
`4,855,550
`
`
`173/170
` 200/5 A
`4,493,377
`1/1985 Gunther et al.
`4,894,493
`1/1990 Smith etal.
`
`. 341/33
`...-neecreecseecsereessee 341/22
`4,495,485
`1/1985 Smith0...
`4,901,074 2/1990 Sinn et al.
`
`
`..
`.. 340/635
`4,920,343 4/1990 Schwartz .......
`seveeeee 341/33
`4,529,968
`7/1985 Hilsum et al.
`
`2
`
`

`

`U.S. Patent
`
`Feb. 23, 1993
`
`Sheet 1 of 5
`
`5,189,417
`
`FIG.1
`
`3
`
`

`

`U.S. Patent
`
`Feb. 23, 1993
`
`Sheet 2 of 5
`
`5,189,417
`
`wo
`4
`
`wo
`
`wy CONTROL
`
`FIG.2
`
`a°)
`
`+©
`
`4
`
`

`

`U.S. Patent
`
`Feb. 23, 1993
`
`Sheet 3 of 5
`
`5,189,417
`
`FIG.
`
`Ja
`
`FIG.
`
`3b
`
`
`
`
` I
`
`;
`
`REFERENCE VOLTAGE
`
`FIG. 3c
`
`LI
`
`I
`
`SETPOINT
`
`THRESHOLD
`3d
`
`FIG.
`
`5
`
`

`

`U.S. Patent
`
`Feb, 23, 1993
`
`Sheet 4 of 5
`
`5,189,417
`
`INITIALIZE
`VARIABLES
`
`—-
`
`64
`
`
`
`
`
`
`
`
`
`
`DONE
`
`82
`
`RESET
`COLUMN
`
`WITH
`ROW?
`
`NO
`
`INCREMENT
`ROW
`
`84
`
`_YES (on
`
`86
`
`SELECT ROW
`AND COLUMN
`
`RESET TIMER
`
`OUTPUT PULSE
`
`READ TIMER
`
`CALCULATE
`PULSE WIDTH
`
`SAVE PULSE WIDTH
`(THIS PASS)
`
`66
`
`68
`
`70
`
`72
`
`74
`
`76
`
`78
`
`YES
`
`DONE
`WITH
`COLUMN?
`
`SELECT NEXT
`COLUMN
`
`FIG. 4a
`
`6
`
`

`

`U.S. Patent
`
`Feb. 23, 1993
`
`Sheet 5 of 5
`
`5,189,417
`
`90
`
`92
`
`YES
`
`SELECT SWITCH
`
`PULSE
`WIDTH CHANGE
`SET POINT?
`
`
`
`
`98
`
`INC SWCNT
`
`woIns
`
`SAVE SWIDEN
`
`96
`
`
`
`108
`
`102
`
`NO
`
`
`
`.
`
`ADJUST THRESH’S
`
`104
`
`OUTPUT SWIDEN
`
`SWIDEN = FFH
`
`SWIDEN = 0
`
`
`
`
`
`EXIT
`
`106
`
`FIG. 4b
`
`7
`
`

`

`1
`
`5,189,417
`
`DETECTION CIRCUIT FOR MATRIX TOUCH PAD
`
`2
`to a reference pulse width to distinguish between a
`touch and no-touch condition for each touch pad.
`According to another aspect of the invention, a plu-
`rality of amplifier means are provided, each of which is
`5 connected to one of the sense lines for amplifying the
`sensed signal on the associated sense line. In this man-
`ner, each amplifier may have a gain thatis established
`independently of the other amplifiers so that the gains
`may be selected to normalize amplifier outputs for
`touched and no-touched responses to provide a coarse
`correction for differences in the characteristics of each
`sense line. A plurality of demodulating means, each
`responsive to one of the amplifier means, may be pro-
`vided to produce pulses having widths that are propor-
`tional to the amplitude of the associated amplified sense
`signal. The pulses are provided to a control circuit
`having an input, measuring means for measuring the
`width of pulses provided to the input and judging means
`for comparing each pulse width measurementtoa tefer-
`ence pulse width. Multiplexing means may also be pro-
`vided for selectively connecting each of the demodulat-
`ing means to the control circuit input means. In this
`manner, additional hardware correction may be pro-
`vided in the individual demodulating means in order to
`reduce the amount of software correction that is re-
`quired.
`In the preferred embodiment, each demodulating
`means includes a comparator having a reference input
`to produce pulse having a width that is proportional to
`the amplitude of the sensed signal. The width of the
`pulse is measured by a timer input of a microprocessor.
`These and other objects, advantages and features ofthis
`invention will become apparent upon review of the
`following specification in conjunction with the draw-
`ings.
`
`BACKGROUNDOF THE INVENTION
`This invention relates generally to touch detection
`circuits and, moreparticularly, to detection circuits for
`use with a matrix arrangement of touch pads in a key-
`board.
`It has been known to arrange touch pads in a matrix
`and to utilize multiplexing techniques in order to reduce
`the number of interconnections extending between the
`matrix of touch pads and a detection circuit. For a key-
`pad ofsixteen keys,it is necessary to provide four drive
`lines to apply signals to the matrix and four sense lines
`to sense the touched and non-touched condition ofthe
`sixteen touch pads. One problem with such arrange-
`ment is that variations in lead length and touch pad
`layouts cause variations in the sensed signals received
`on the sense lines depending upon theindividual touch
`pads being touched.
`Onesolution to this problem is proposed in U.S.Pat.
`No.4,145,748 issued to Eichelbergeretal. for a SELF-
`OPTIMIZING TOUCH PAD SENSOR CIRCUIT
`which converts voltages associated with each of the
`touch padsinto digital values, with the digital reading
`obtained for the no-touch condition for each touch pad
`being stored ina memory. A control logic circuit cycles
`through all touch pads and comparesthe digital read-
`ings obtained from each of the touch pads to the value
`of the no-touch reading for the respective touch pad
`which has been stored in the memory. Whena signifi-
`cant departure from the no-touch condition is obtained,
`a touch indicationis given for that particular touch pad.
`The control updates the no-touchdigital output in the
`system memory during an optimization mode. The diffi-
`BRIEF DESCRIPTION OF THE DRAWINGS
`culty with the system disclosed in Eichelbergeretal. is
`FIG.1is a perspective view of a matrix touch pad
`that the digital output is produced by a charge transfer
`analog-to-digital converter which is slow,is relatively
`useful with the present invention,
`FIG.2 is a schematic diagram of a detection circuit
`expensive and requires specialized controlsignals from
`the controllogic circuit. Furthermore, all compensation
`according to the invention;
`FIGS. 3A through 3Dare diagramsillustrating signal
`techniques are executed in logic becauseall signals are
`wave formsin thecircuit illustrated in FIG. 2; and
`sensed through a common analog-to-digital converter.
`FIGS. 4A and 4Billustrate a flow chart of software
`A hardware-oriented solution to the variation in re-
`sponse from onesenseline to anotheris set forth in US.
`useful with the present invention.
`Pat. No. 4,413,252 issued to Tyler et al. for a CAPACI-
`DESCRIPTION OF THE PREFERRED
`TIVE SWITCH AND PANEL.In Tyleret al. capaci-
`EMBODIMENT
`tive trim tabs are provided for each switch to compen-
`sate for differences in stray capacitance from switch to
`switch. Each ofthe individual tabs requires trimming to
`provide the appropriate compensation. This approachis
`both tedious and time consuming.
`
`40
`
`45
`
`50
`
`SUMMARYOF THE INVENTION
`The present invention is embodied in a circuit for
`detecting user contact of one of a plurality of touch
`padsincluding a plurality of drive lines and a plurality
`of sense lines. Each of the touch pads is coupled to a
`different combination of the drive and sense lines from
`any of the other touch pads. A driver circuit means
`provides pulsed drive signals to each of the drivelines
`and sense circuit means senses signals produced on each
`sense line. Accordingto one aspect of the invention, the
`sense circuit means includes means for producing a
`pulse having a width that is proportional to the ampli-
`tude ofeach of the sensed signals. Control circuit means
`measures the width of the pulses produced by the sense
`circuit means and compares each measured pulse width
`
`6
`
`65
`
`Referring now specifically to the drawings and the
`illustrative embodiments depicted therein, a matrix
`touch pad assembly 10 includes a rigid outer panel 12
`including a non-flexible dielectric member 14 and trans-
`parent conductive touch pads 16 formed on an outer
`surface 18 of dielectric member 14 (FIG.1). Touch pad
`assembly 10 additionally includes an inner panel 20
`having a dielectric member 22, which may be flexible, a
`plurality of pairs of conductive pads 24a, 246 and con-
`ductive leads 26 extending to conductive pads 24a, 24b.
`Conductive pads 24a, 24b and conductive leads 26 are
`printed on surface 27 of dielectric member 22 facing
`dielectric member 14 to which inner panel 20 is at-
`tached by an adhesive (not shown). Each touch pad 16
`overlies a pair of conductive pads 24a, 24d to define a
`capacitive switch 28.
`Matrix touch pad assembly 10 is interconnected with
`a detection circuit 30 through conductive leads 26
`(FIG. 2). Conductive leads 26 are grouped into drive
`lines 32a-32d and sense lines 34a-34d. Each touch
`
`8
`
`

`

`_ tA
`
`20
`
`25
`
`3
`
`5,189,417 _
`4
`3
`switch 28 is connected with a different combination of
`a gain for each amplifier 40c-40d that provides peak
`drive lines 32a-32d and sense lines 34a-34d. A control
`signal amplitudes on lines 46a—46d that are substantially
`matched for touched and non-touched conditions ofall
`circuit 36, which in the illustrated embodimentis micro-
`sense lines 34c-34d. This provides a coarse correction
`processor controlled, provides timing signals to a pulse
`to compensate for the variations in stray capacitance,
`drive circuit 38 which produces pulses sequentially-on
`drive lines 32¢-32d. As best seen by reference to FIG..2,
`lead line length, pad configuration, and other factors
`causing variation from one sense line to the next. This
`a pulse applied to one of drive lines 32a-32d is applied
`may be accomplished either by providing adjustable
`to an entire “row” of capacitive switches 28. Each of
`feedback resistors 44a-44d or by providing fixed resis-
`sense lines 34a-34d, which is responsive to an entire
`tors having values that are matched to a particular con-
`column of capacitive switches 28, is connected to the
`figuration of. touch pad assembly 10. Signal strength
`input of an amplifier 40a-40d. Each amplifier 40e-40d
`variations that remain on output lines 46c-46d from
`includes an amplification means, such as an operational
`amplifiers 40a-40d may be further corrected by select-
`amplifier 42¢-42d and a gain control means such as a
`ing individual reference voltage levels U1-U4 for com-
`feedback resistor 440-44. Each amplifier 40a—40d pro-
`parators 48c-48d. In this manner, the pulse output of
`duces an output on line 46a-46d which is provided to
`comparators 48a-48d may be maderelatively uniform
`the non-inverting input of a comparator 48a-48d. The
`for all comparator outputs for both touched and non-
`inverting input for each comparator 48a-48d is con-
`touched conditions. In a preferred embodiment, refer-
`nected to a oneofplurality of reference voltage U1-U4.
`ence voltage levels U1-U4 are made the sameforall
`Outputs 50a-50d of comparators 48a-48d are provided
`sense lines and all coarse corrections are made bysuit-
`as inputs to a demultiplexing circuit, or demultiplexer,
`able selection of the gains for amplifiers 40a-40d.
`52. Demultiplexer 52 provides an output on a line 54
`Control 36 includes a software program 62 which is
`which is provided as an input to a timer 56, whose
`initialized at 64 and selects (66) the switch residing at
`output onaline 58 is provided as an input to control 36.
`thefirst row and column and,for the particular row and
`Control 36, provides timing signals on a line 60 to de-
`column, resets timer 56 at 68(FIG. 4a). The program
`multiplexer 52.
`Eachtimea pulse, having the wave form illustrated in
`causes pulse drive circuit 38 to produce an output pulse
`at 70 on the appropriate one of drive lines 32¢-32d. The
`FIG.3A is produced on oneofthe drive lines 32a-32d,
`program additionally causes control 36 to produce the
`a differentiated form of the pulse is received on lines
`appropriate signals on line 60 for the demultiplexer to
`34a-34d, as illustrated in FIG. 3B. After being amplified
`select the sense line 50a~50d for the column. Timer56 is
`by amplifiers 40c-40d, each differentiated signal is com-
`then read (72) and the pulse width is determined (74)
`pared against
`the associated reference level U1-U4
`which are established at values that are less than than
`from the digital output line 58. This numberis stored
`(76) in a memorylocation allocated to the particular
`peak value of the differentiated signal, as illustrated in
`FIG.3C,for both touch and no-touch conditions. The
`switch being read during this pass through the program
`(THIS PASS). Control then passes to 78 and 80 for
`resulting output of comparators 46a—46d are pulses
`repetition of the above sequence for all columns in a
`having widths that are proportional to the amount of
`row and to 82 and 84 for completion of all rows of
`time that
`the corresponding differentiated signal
`is
`abovethe level of the associated threshold U1-U4.If a
`switches 28 in the matrix.
`After all switches have been processed, control
`user actuates a capacitive switch 28 by touching the
`associated conductive touch pad 16, the differentiated
`passes to 90 (FIG. 4B) where the number stored at 76
`for the first switch is compared at 92 with another num-
`signal on lines 34a-34d decreases in amplitude asillus-
`ber (THRESHOLD)stored in another memory loca-
`trated by the wave form I in FIG. 3C. Because the
`tion allocated to that switch in order to provide judging
`attenuated wave form, resulting from the users body
`forming a path to the ground, has a proportionately
`means for judging whether the switchis active.If it is-
`determined at 92 that the pulse width (THIS PASS)is
`lower amplitude throughout
`the signal, a narrower
`less than THRESHOLD bya given amount (SET
`portion of signal I will be below the threshold. The
`POINT), control passes
`to 94 where a counter
`result is a narrower pulse J (FIG. 3D) provided on the
`(SWCNT) is incremented and to 96 where the identity
`output of the associated comparator 48a-48d. When a
`of the active switch is stored. If it is determined at 92
`particular capacitive switch is not being touched, the
`that the pulse width for the switch THIS PASSis not
`wave form of the differentiated signal appears as II in
`FIG. 3C which results in a wider output pulse I from
`less than the THRESHOLDbythe given amount (SET
`the associated comparator,as illustrated in FIG. 3D.
`POINT), control passes to 98 where it is determined
`whether there remains any switches to be tested. All
`Control circuit 36 synchronizes pulse drive circuit 38
`switches 28 are examined in this manner.
`and multiplexer 52 such that the output of demultiplexer
`52 on line 54 represents sixteen serial pulses whose
`After all switches 28 are examined, control passes to
`100 whereit is determined whether any switches are
`widths represent the state of the sixteen switches 28.
`active by examining the content of the SWCNT regis-
`Theserial pulses on line 54 are provided to timer 56
`ter. If it is determined at 100 that zero switches are
`which, for each pulse, measures its width and provides
`active, control passes to 102 where the values of the
`a digital signal on line 58 to control 36 representing the
`THRESHOLDforall of the switches are adjusted
`width for each pulse. In this manner, control 36 is repet-
`according to the most recently determined pulse width
`itively provided with information regarding the condi-
`values. Control! then passes to 104 where the value of a
`tion of each capacitive switch 28.
`register (SWIDEN) is reset to zero. SWIDENis a reg-
`Gain control means 44a-44d for each amplifier
`40a-40d is independentof the other gain control means.
`ister representing the identity of a switch which be-
`comes active, or touched, and is available as control
`In this manner,variations in the characteristic responses
`of sense lines 34a-34d, as a result of lead line length,
`input for devices (not shown) being controlled by the
`touch pad assembly. The program is exited at 106. Ifit
`stray capacitance, variation in the shape of pads 244,
`is determined at 100 that
`there is some number of
`246 and the like, may be compensated for by providing
`
`40
`
`45
`
`60
`
`65
`
`"
`
`9
`
`

`

`5,189,417
`
`30
`
`35
`
`40
`
`45
`
`5
`switches greater than zero that are active, control
`passes to 108 where it is determined whether only one
`switch is active. If so, contro] passes to 110 where the
`identity of the active switch loaded into SWIDENand
`is outputted as the output of detection circuit 30.If it is
`determined at 108 that some number other than one
`switch is active, control passes to 112 where an error
`code, such as FFH is loaded into SWIDENand output-
`ted to indicate that an illegal condition, namely, more
`than one capacitive switch being actuated at a time, is
`provided.
`,
`:
`Program 62 provides a software adjustment to the
`value of the thresholds for each switch to compliment
`the coarse adjustments made by amplifiers 40c~40d and,
`optionally, by comparators 48c-48d. Because the coarse
`adjustment is made in hardware, the width ofthe pulse
`produced on lines 502-50d may be made close to the
`window dictated by the width of the pulses produced
`by pulse drivecircuit 38, without exceeding such win-
`dow. Furthermore, because the software adjustments
`are “fine adjustments” there is less opportunity for er-
`rors to occur. By individually amplifying each sense
`line, not only is a coarse adjustment provided, but the
`supply voltage used to apply pulses by pulse driver
`circuit 38 may be reduced from 12 volts bipolar to 5-10
`volts unipolar. In the illustrated embodiment, the pulses
`produced by pulse drive circuit 38, and hence the win-
`dow in which the pulses are measured by timer 56 is 255
`microseconds which allowsall switches 28 to be moni-
`tored approximately every 4 milliseconds.
`While the inventionis illustrated utilizing compara-
`tors in order to demodulate the signal sensed by the
`sense lines and independently amplified by the amplifi-
`ers, other demodulating means are possible. Addition-
`ally, the use of comparators, in which the sensed differ-
`entiated pulses exceed a threshold in order to produce a
`pulsed output whose width is proportional to the condi-
`tion of the switch, may be used in other touch respon-
`sive systems, for example, those which multiplex the
`signals from the sense lines prior to demodulation of the
`information from the sensed signals. Although timer 56
`is illustrated as a separate device, in a preferred embodi-
`ment, timer 56 is a timed input of a microprocessor and
`line 58 is an internal pathway in the microprocessor.
`Other, changes and modifications to the specifically
`described embodiments can be carried out without de-
`parting from the principles of the invention, which is
`intended to be limited only by the scope of the ap-
`pended claims, as interpreted according to the princi-
`ples of patent law including the Doctrine of Equiva-
`lents.
`Weclaim:
`1. A circuit for detecting user contact of one of a
`plurality of touch pads comprising:
`a plurality of drive lines and a plurality of sense lines,
`each of said touch pads being coupled to a differ-
`ence combinationofsaid drive and sense lines from
`any other of said touch pads;
`driver circuit means for providing pulsed drive sig-
`nals to said drive lines;
`.
`at least one amplifier having an input connected at a
`given time to one ofsaid sense lines, an output and
`gain meansforestablishing the gain ofsaid at least
`one amplifier; and
`demodulating means responsive to said at least one
`amplifier output for determining which of said
`touch pads is being contacted by a user, wherein
`said demodulating means includes at least one com-
`
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`parator means responsive at said given time to the
`amplified sensed signa! of said one of said sense
`lines for producing a pulse having a width thatis a
`function of the time that the associated amplified
`sensed signal is above a given referencelevel.
`2. The circuit in claim 1 wherein each of said gain
`means is independentof the other said gain means.
`3. The circuit in claim 1 wherein said given reference
`level is individually selected for each of said demodulat-
`ing means.
`_ 4. The circuit in claim 1 wherein said demodulating
`means further includes timer means for measuring the
`length of time that a pulse is present.
`5. The circuit in claim 1 wherein said demodulating
`means further includes means for establishing a refer-
`ence pulse width associated with each of said touch
`pads and adjustment means for adaptively adjusting
`each of said reference pulse widths.
`6. A circuit for detecting user contact of one of a
`plurality of touch pads comprising:
`a plurality of drive lines and plurality of sense lines,
`eachofsaid touch pads being coupledto a different
`combination of said drive and sense lines from any
`other of said touch pads;
`driver circuit means for providing a pulsed drive
`signal to each said drive line;
`sense circuit means for sensing signals produced on
`said sense lines, said sense circuit means including
`meansfor producing a pulse having a width that is
`proportional to the amplitude of each sensed signal;
`and
`control circuit means for measuring the width of
`pulses produced by sense circuit means and com-
`paring each width to a reference pulse width.
`7. The circuit in claim 6 wherein said sense circuit
`means includes comparison meansfor producing pulses
`having widths that are a function ofthe time that signals
`on associated sense lines are above a given reference
`level.
`8. The circuit in claim 6 wherein said sense circuit
`means includes a plurality of comparator means each
`responsive to the signal on one ofsaid sense lines for
`producing a pulse having a width that is a function of
`the time that the signal on the associated sense line is
`above a given reference level.
`9. The circuit in claim 8 including means for provid-
`ing an individual reference level for each of said com-
`parator means such that said reference level for each
`comparator means maybe different from that for other
`comparator means.
`10. Thecircuit in claim 6 wherein said control circuit
`means includes timer means for measuring the length of
`time that a pulse is present and means for providing
`each of said pulses to said timer means such that the
`width of each pulse may be determined.
`11. Thecircuit in claim 6 wherein said control circuit
`means includes pulse drive circuit means for causing
`said drive circuit means to provide said pulses accord-
`ing to a predetermined sequence and multiplexing
`means for establishing the touch pad associated with
`each pulse.
`12. Thecircuit in claim 6 wherein said control circuit
`means includes meansfor establishing a reference pulse
`width associated with each of said touch pads and ad-
`justment means for adaptively adjusting each ofsaid
`reference pulse width.
`13. A circuit for detecting user contact of one of a
`plurality of touch pads comprising:
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`a plurality of drive lines and a plurality of sense lines,
`eachof said touch pads being coupled to a different
`combination of said drive and sense lines from any
`other of said touch pads;
`driver circuit means for providing pulsed drive sig-
`nals to said drive lines;
`a plurality of amplifier means each connected with
`one of said sense lines for amplifying the sensed
`signal on the associated said sense line;
`a plurality of demodulating means each responsive to
`one of said amplifier means for producing a pulse
`having a width that is proportional to the amph-
`tude of the associated amplified sensed signal;
`control circuit means including an input, measuring
`means for measuring the width of pulses provided
`to said input and judging means for comparing
`each measurementto a reference pulse width; and
`multiplexing means for selectively connecting each
`said demodulating means to said control circuit
`means input.
`14. Thecircuit in claim 13 wherein each said demodu-
`lating means includes a comparator meansresponsive to
`the associated amplified sensed signal for producing a
`pulse having a width that is a function of the time that
`the associated amplified sensed signal is above a given
`reference level.
`:
`15. The circuit in claim 14 wherein said given refer-
`ence levelis individually selected for each of said de-
`modulating means.
`16. Thecircuit in claim 13 wherein each of said ampli-
`fying means includes means for establishing its gain
`independently of the other said amplifying means.
`17. The circuit in claim 13 wherein said measuring
`meansincludes timer meansfor measuring the length of
`time that a pulse is present.
`18. The circuit in claim 13 wherein said control cir-
`cuit means includes means for coordinating said drive
`circuit means providing said pulses and said demulti-
`plexing meansin order to establish the touch pad associ-
`ated with each pulse.
`19. The circuit in claim 13 wherein said judging
`means includes meansfor establishing a reference pulse
`width associated with each of said touch pads and ad-
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`justment means for adaptively adjusting each of said
`reference pulse width.
`20. A circuit for detecting user contact of one of a
`plurality of touch pads comprising:
`a plurality of drive lines and a plurality of sense lines,
`eachof said touch pads being coupled to a different
`combination of said drive and sense lines from any
`other of said touch pads;
`driver circuit means for providing pulsed drive sig-
`nals to said drive lines;
`a plurality of amplifiers, each amplifier having an
`input connectedto oneofsaid senselines, an output
`and gain means for establishing the gain of said
`amplifier;
`a plurality of comparators, each comparator having
`an input connected to the output of one of said
`amplifiers, an output and meansestablishing a ref-
`erence level, wherein said comparator outputis in
`a given state whenever the signal to the input is
`greater than the referencelevel for that particular
`comparator;
`a timer adapted to measuring the width of pulses;
`multiplexing means for selectively connecting each
`said comparator output to said timer; and
`judging means responsive to said timer for determin-
`ing whether each pulse has a predetermined rela-
`tionship to a reference pulse width.
`21. The circuit in claim 20 wherein said reference
`level for each of said comparators is independentof the
`other said reference levels.
`:
`22. The circuit in claim 20 wherein each of said gain
`meansis independent of the other gain means.
`23. The circuit in claim 20 further including means
`for coordinating said drive means providing said pulses
`and said demultiplexing meansin order to establish the
`touch pad associated with each pulse.
`24. The circuit in claim 20 wherein said judging
`meansincludes meansforestablishing a reference pulse
`width associated with each of said touch pads and ad-
`justment means for adaptively adjusting each said refer-
`ence pulse width.
`*
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