.
`United States Patent
`Caldwell et a1.
`
`1191
`
`[54] DETECTION CIRCUIT FOR MATRIX
`TOUCH pAD
`
`[75]
`
`[73]
`
`Inventors: Divid W- Caldwell; Nicholas W.
`Medendorp, both of Holland, Mich.
`_
`.
`ASS‘ET‘CCZ D9'meuy 00‘1””“0ns H0113“,
`Mich-
`
`,
`[21} APPLNO" 598429
`[22] Filed;
`0d, 15, 1990
`[51]
`Int. Cl.5 ............................................ H03M 11/20
`[52] us. Cl. ........................................ 341/26; 341/34;
`364/189
`[58] Field of Search ....................... 341/33, 34, 26, 22,
`.
`.
`.
`.
`341/24, ZOO/600’ 400/479'1’ 364/189’ 379/368
`References Cited
`US. PATENT DOCUMENTS
`
`[56]
`
`3,3612: 22:2;
`iffiin'etai""""""
`25032311121
`
`3:200:304
`8/1965 Atkinsetal...
`...... 361/179
`, 351/179
`3,200,305
`8/1965 Atkins et al.
`
`:. 361/179
`3,200,306
`8/1965 Atkins et al.
`
`.. 331/111
`3,254,313 5/1966 Atkins et 31.
`
`3,275,897 9/1966 Atkins et :11.
`
`" 337%?
`3,549,909 12/1970 Adelson .....
`
`.. 318/345
`3,641,410 2/ 1972 Vogelsberg
`
`.. 318/446
`3,651,391 3/ 1972 Vogelsbcrg
`
`.. 315/208
`3,666,988
`5/1972 Bellis
`, 173/13
`3,798,370
`3/1974 Hurst ..
`
`3,846,791 11/ 1974 Foster
`. 341/33
`. 315/34
`8/1975 Barkan et 3
`3,899,713
`
`3,911,215 10/1975 Hurst et a1.
`- 178/13
`6/1976 Alexander ..
`3,965,465
`-- 340/527
`
`3,984,757 10/1976 Got! et a1.
`..
`
`"""323%};
`4,016,453 4/1977 Moennig
`
`307/116
`4,031,408 6/ 1977 Holz .......
`4,056,699 11/1977 Jordan .......
`,, zoo/5 A
`
`1/1978 Talmage et a1.
`4,071,689
`..... 178/18
`
`4,090,092 5/1978 Serrano
`313:9};
`7/1978 Stone .........
`4,101,805
`
`3:.‘340/531
`7/1978 Grimes et a1.
`4,101,886
`
`307/116
`4,119,864 [0/1978 Petrizio ..
`
`. 200/52 R
`4,123,631 10/1978 Lewis .....
`
`........... 307/308
`4,136,291
`1/1979 Waldron
`
`IIIIlIlIlIIIlIllIlllllllllllllllllllIlllllllllIlllllllllllllllllllllllllll
`U5005189417A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,189,417
`Feb. 23, 1993
`
`............. 364/862
`4,145,748 3/1979 Eichelberger et al.
`340/565
`._ 315/362
`4,152,629.
`5/1979 Raupp
`
`.
`4,159,473 6/1979 Senk ...............
`
`361/280
`7/1979 Castleberry eta].
`4,161,766
`340/310 B
`4,174,517 11/ 1979 Mandel .............
`
`...307/116
`4,210,822 7/1980 Wem ................
`
`4,211,959 7/1930 Deavenport 61111.
`.. 315/362
`7/1930 Conner .............
`4,213,061
`307/116
`
`.. 178/18
`9/1980 Gibson 6131.
`4,220,815
`9/1980 Grimes eta].
`4,223,301
`340/500
`
`
`4,237,386 12/1980 Instance
`307/116
`307/252 11
`4,264,831
`4/1981 Wem,
`
`
`9/1981 Wem ........
`307/116
`4,289,972
`
`307/308
`4,289,980 9/1981 McLaughlin
`9/1981 Eichelberger et a1.
`.
`4,290,052
`340/33
`
`4,291,303
`9/1981 Cutler ct all ......1.
`3:53;?
`
`4,293,987 10/1981 Gottbrecht 61a.
`. 2
`.. 219/1055 B
`4,304,976 12/1981 Gottbrecht et a].
`(List continued on next page.)
`
`Primary Examiner—Donald J. Yusko
`Assistant Examiner-Michael Horabik
`A‘mmey'Agm'o’ F”m*P“°e’H°“°VC‘d’C°°PeL
`Dewitt & Litton
`
`[57]
`ABSTRACT
`A circuit for detecting user contact of one of a plurality
`of touch pads includes a plurality of drive lines and a
`plurahty of sense lines coupled with the touch pads. A
`sense circuit responsive to the signals on the sense lines
`produces a pulse having a width that is proportional to
`the amplitude of each of the sense signals. A control
`circuit measures the width of the pulses produced by
`the sense circuit and compares each measured pulse
`width to a reference pulse width to distinguish between
`a touch and no-touch condition for each touch pad. The
`sense circuit is illustrated in the form of a comparator
`having a threshold input that is always exceeded by the
`sense signal to produce the variable width pulse. Sepa»
`rate amplifiers may be provided for each sense line.
`
`24 Claims, 5 Drawing Sheets
`
`APPLE 1018
`
` 1
`
`1
`
`APPLE 1018
`
`

`

`5,139,417
`Page 2M
`
`U.S. PATENT DOCUMENTS
`
`318/55
`4,323,829 4/1982 Witney et a1.
`...... 307/116
`4,360,737 11/1982 Leopold ..
`
`.. 340/711
`4,374,381
`2/1983 Ng et a1.
`4,380,040 4/1983 Posset ......
`361/290
`
`. 341/33
`4,394,643
`7/1933 Williams
`
`8/1983 Frame .....
`4,400,758
`361/290
`
`. 341/26
`4,405,917
`9/1983 Chai
`..
`. 341/26
`4,405,918
`9/1983 Wall ct 3.1.
`
`. 341/33
`4,413,252 11/1983 Tyler et a1.
`
`3/1984 Calandrello er a1.
`200/519
`4,439,647
`..' 340/712
`4,476,463 10/1984 Ng et a].
`
`173/170
`4,493,377
`1/1985 Gunther et 2.1.
`
`4,495,485
`1/1985 Smith .............
` . 341/33
`..
`.. 340/635
`4,529,968
`7/1985 Hilsum :1 a1.
`
`4,535,254
`4,550,310
`4,561,002
`4,567,470
`4,584,519
`4,614,937
`4,651,133
`4,709,228
`4,731,694
`4,736,190
`4,740,781
`4,743,895
`4,855,550
`4,894,493
`4,901,074
`4,920,343
`
`8/1985
`10/1985
`12/1985
`1/1986
`4/1986
`9/1986
`3/1987
`11/1987
`3/1988
`4/1988
`4/1988
`5/1988
`8/1989
`1/1990
`2/1990
`4/1990
`
`
`
`
`
`Khatri
`307/38
`
`Yamaguchl e1 2 .
`. 341/33
`Chui ...................
`. 341/26
`Yoshikawa et al.
`. 341/33
`Groudis .................
`323/245
`
`Poujois
`..... 341/33
`Ganesan :1 2.1.
`341/33
`
`Huck‘mg et al.
`341/26 X
`Grabner et a].
`361/280
`..... 341/22
`Fiorella
`
`Brown .....
`340/712
`
`Alexander ..
`340/712
`Schultz, Jr.
`200/600
`
`Smith ct a].
`.. 200/5 A
`..
`..... 341/22
`Sim) et al.
`
`Schwartz .......
`341/33
`
`2
`
`

`

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

`

`US. Patent
`
`Feb. 23, 1993
`
`Sheet 2 of 5
`
`5,189,417
`
`(D
`H
`
`(D
`
`LO
`CONTROL
`
`FIG.2
`
`
`
`fig.
`
`
`III‘7
`
`III.
` 2'6-
`III
`
`
`
`
`
`34d
`
`4
`
`

`

`US. Patent
`
`Feb. 23, 1993
`
`Sheet 3 of 5
`
`5,189,417
`
`FIG.
`
`30
`
`FIG.
`
`3b
`
`
`
`
`
`REFERENCE VOLTAGE
`
`II
`
`FIG .
`
`3C
`
`.- 1
`
`n
`
`SETPOINT
`
`THRESHOLD
`3d
`
`FIG .
`
`5
`
`

`

`US. Patent
`
`Feb. 23, 1993
`
`Sheet 4 of 5
`
`5,189,417
`
`lNlTIALlZE
`VAR|ABLES
`
`‘
`
`SELECT ROW
`AND COLUMN
`
`
`
`
`
`
`RESET HMER
`
`OUTPUT PULSE
`
`READ TIMER
`
`CALCULATE
`PULSE WIDTH
`
`SAVE PULSE WIDTH
`
`(THIS PASS)
`
`64
`
`66
`
`68
`
`7O
`
`72
`
`.
`
`74
`
`76
`
`.
`
`
`
`
`
`DONE ,YES wWITH
`
`
`78
`
`YES
`
`DONE
`WWH
`COLUMN?
`
`RESET
`COLUMN
`
`SELECT NEXT
`COLUMN
`
`,
`
`'
`
`
`
`‘ FIG. 4a
`
`ROW?
`
`NO
`
`INCREMENT
`ROW
`
`86
`
`6
`
`

`

`US. Patent
`
`Feb. 23, 1993
`
`Sheet 5 of 5
`
`5,189,417
`
`’
`
`SELECT SWITCH
`
`
` PULSE
`
`WIDTH CHANGE
`
`
`SET POINT”
`
`
`
`
`
` DONE
`ALL
`SWITCHES?
`
`
`YES
`
`‘®
`
`OUTPUT SWIDEN
`
`94
`
`INC SWCNT
`
`SAVE SWIDEN
`
`96
`
`90
`
`92
`
`YES
`
`98
`
`YES
`
`
`
`
`
`SWIDEN = FFH
`
`SWTDEN = O
`
`ADJUST THRESH'S
`
`102
`
`104
`
`V
`
`EXIT
`
`106
`
`FIG. 4b
`
`7
`
`

`

`1
`
`5,189,417
`
`DETECTION CIRCUIT FOR MATRIX TOUCH PAD
`
`BACKGROUND OF THE INVENTION
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`This invention relates generally to touch detection
`circuits and, more particularly, 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 of sixteen 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 of the
`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 the individual touch
`pads being touched.
`One solution to this problem is proposed in US Pat.
`No. 4,145,748 issued to Eichelberger et al. for a SELF-
`OPTIMIZING TOUCH PAD SENSOR CIRCUIT
`which converts voltages associated with each of the
`touch pads into digital values, with the digital reading
`obtained for the no-touch condition for each touch pad
`being stored in a memory. A control logic circuit cycles
`through all touch pads and compares the 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. When a signifi-
`cant departure from the no-touch condition is obtained,
`a touch indication is given for that particular touch pad.
`The control updates the no-touch digital output in the
`system memory during an optimization mode. The diffi-
`culty with the system disclosed in Eichelberger et a1. is
`that the digital output is produced by a charge transfer
`analog—toodigital converter which is slow, is relatively
`expensive and requires specialized control signals from
`the control logic circuit. Furthermore, all compensation
`techniques are executed in logic because all signals are
`sensed through a common analog-to-digital converter.
`A hardware-oriented solution to the variation in re-
`sponse from one sense line to another is set forth in US.
`Pat. No. 4,413,252 issued to Tyler et al. for a CAPACI-
`TIVE SWITCH AND PANEL. In Tyler et a1. capaci-
`tive trim tabs are provided for each switch to compen-
`sate for differences in stray capacitance from switch to
`switch. Each of the individual tabs requires trimming to
`provide the appropriate compensation. This approach is
`both tedious and time consuming.
`
`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
`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 that is 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 measurement to a refer-
`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 of this
`invention will become apparent upon review of the
`following specification in conjunction with the draw-
`ings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a perspective view of a matrix touch pad
`useful with the present invention;
`FIG. 2 is a schematic diagram of a detection circuit
`according to the invention;
`FIGS. 3A through 3D are diagrams illustrating signal
`wave forms in the circuit illustrated in FIG. 2; and
`FIGS. 4A and 4B illustrate a flow chart of software
`useful with the present invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`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 240, 24b and con-
`ductive leads 26 extending to conductive pads 24a, 24b.
`Conductive pads 240, 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, 24b 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 320—32d and sense lines 34a—34d. Each touch
`
`45
`
`SO
`
`55
`
`65
`
`SUMMARY OF THE INVENTION
`
`The present invention is embodied in a circuit for
`detecting user contact of one of a plurality of touch
`pads including 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 drive lines
`and sense circuit means senses signals produced on each
`sense line. According to 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 of each 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
`
`8
`
`

`

`10
`
`15
`
`20
`
`25
`
`so
`
`35
`
`5,189,417 .
`3
`switch 28 is connected with a different combination of
`drive lines 32a-32d and sense lines 34a—34d. A control
`circuit 36, which in the illustrated embodiment is micro-
`processor controlled, provides timing signals to a pulse
`drive circuit 38 which produces pulses sequentially-on
`drive lines 32a—32d. As best seen by reference to FIG.v2,
`a pulse applied to one of drive lines 32a-32d is applied
`to an entire “row" of capacitive switches 28. Each of
`sense lines 34a—34a’, which is responsive to an entire
`column of capacitive switches 28, is connected to the
`input of an amplifier 40a—40d. Each amplifier 400-40d
`includes an amplification means, such as an operational
`amplifier 42a-42d and a gain control means such as a
`feedback resistor 44am Each amplifier 40a—40d pro-
`duces an output on line 46a-46d which is provided to
`the non-inverting input of a comparator 48a-48d. The
`inverting input for each comparator 48a—48d is con-
`nected to a one of plurality of reference voltage Ul—U4.
`Outputs Silo-50¢! of comparators 4841—4841 are provided
`as inputs to a demultiplexing circuit, or demultiplexer,
`52. Demultiplexer 52 provides an output on a line 54
`which is provided as an input to a timer 56, whose
`output on a line 58 is provided as an input to control 36.
`Control 36, provides timing signals on a line 60 to de-
`multiplexer 52.
`Each time a pulse, having the wave form illustrated in
`FIG. 3A is produced on one of the drive lines 320-324
`a differentiated form of the pulse is received on lines
`34a—34d, as illustrated in FIG. 3B. After being amplified
`by amplifiers 40a—40d, each differentiated signal is com-
`pared against
`the associated reference level Ul-U4
`which are established at values that are less than than
`peak value of the differentiated signal, as illustrated in
`FIG. 3C, for both touch and no-touch conditions. The
`resulting output of comparators 46a—4-6d are pulses
`having widths that are proportional to the amount of
`time that
`the corresponding differentiated signal
`is
`above the level of the associated threshold Ul-U4. If a
`user actuates a capacitive switch 28 by touching the
`associated conductive touch pad 16, the differentiated
`signal on lines 34a—34d decreases in amplitude as illus-
`trated by the wave form I in FIG. 3C. Because the
`attenuated wave form, resulting from the users body
`forming a path to the ground, has a proportionately
`lower amplitude throughout
`the signal, a narrower
`portion of signal I will be below the threshold. The
`result is a narrower pulse I (FIG. 3D) provided on the
`output of the associated comparator 480—48d. When a
`particular capacitive switch is not being touched, the
`wave form of the differentiated signal appears as II in
`FIG. 3C which results in a wider output pulse II from
`the associated comparator, as illustrated in FIG. 3D.
`Control circuit 36 synchronizes pulse drive circuit 38
`and multiplexer 52 such that the output of demultiplexer
`52 on line 54 represents sixteen serial pulses whose
`widths represent the state of the sixteen switches 28.
`The serial pulses on line 54 are provided to timer 56
`which, for each pulse, measures its width and provides
`a digital signal on line 58 to control 36 representing the
`width for each pulse. In this manner, control 36 is repet—
`itively provided with information regarding the condi-
`tion of each capacitive switch 28.
`Gain control means “(z-44d for each amplifier
`40a—40d is independent of the other gain control means.
`In this manner, variations in the characteristic responses
`of sense lines 340-344 as a result of lead line length,
`stray capacitance, variation in the shape of pads 24a,
`24b and the like, may be compensated for by providing
`
`4
`a gain for each amplifier 400—4011 that provides peak
`signal amplitudes on lines 460—4641 that are substantially
`matched for touched and non-touched conditions of all
`sense lines 34a—34d. This provides a coarse correction
`to compensate for the variations in stray capacitance,
`lead line length, pad configuration, and other factors
`causing variation from one sense line to the next. This
`may be accomplished either by providing adjustable
`feedback resistors 44a—44d or by providing fixed resis-
`tors having values that are matched to a particular con-
`figuration of, touch pad assembly 10. Signal strength
`variations that remain on output lines Mia—46d from
`amplifiers 40a—40d may be further corrected by select-
`ing individual reference voltage levels U1-U4 for com-
`parators 4822-4811. In this manner, the pulse output of
`comparators 48a-48d may be made relatively uniform
`for all comparator outputs for both touched and non-
`touched conditions. In a preferred embodiment, refer-
`ence voltage levels U1—U4 are made the same for all
`sense lines and all coarse corrections are made by suit—
`able selection of the gains for amplifiers 40a-40d.
`Control 36 includes a software program 62 which is
`initialized at 64 and selects (66) the switch residing at
`the first row and column and, for the particular row and
`column, resets timer 56 at 68(FIG. 4a). The program
`causes pulse drive circuit 38 to produce an output pulse
`at 70 on the appropriate one of drive lines 32a—32d. The
`program additionally causes control 36 to produce the
`appropriate signals on line 60 for the demultiplexer to
`select the sense line 50a—50d for the column. Timer 56 is
`then read (72) and the pulse width is determined (74)
`from the digital output line 58. This number is stored
`(76) in a memory location allocated to the particular
`switch being read during this pass through the program
`(THIS PASS). Control then passes to 78 and 80 for
`repetition of the above sequence for all columns in a
`row and to 82 and 84 for completion of all rows of
`switches 28 in the matrix.
`After all switches have been processed, control
`passes to 90 (FIG. 4B) where the number stored at 76
`for the first switch is compared at 92 with another num-
`ber (THRESHOLD) stored in another memory loca-
`tion allocated to that switch in order to provide judging
`means for judging whether the switch is active. If it is‘
`determined at 92 that the pulse width (THIS PASS) is
`less than THRESHOLD by a given amount (SET
`POINT), control passes
`to 94- where a counter
`(SWCNT) is incremented and to 96 where the identity
`of the active switch is stored. If it is determined at 92
`that the pulse width for the switch THIS PASS is not
`less than the THRESHOLD by the given amount (SET
`POINT), control passes to 98 where it is determined
`whether there remains any switches to be tested. All
`switches 28 are examined in this manner.
`After all switches 28 are examined, control passes to
`100 where it is determined whether any switches are
`active by examining the content of the SWCNT regis-
`ter. If it is determined at 100 that zero switches are
`active, control passes to 102 where the values of the
`THRESHOLD for all of the switches are adjusted
`according to the most recently determined pulse width
`values. Control then passes to 104 where the value of a
`register (SWIDEN) is reset to zero. SWIDEN is a reg—
`ister representing the identity of a switch which be-
`comes active, or touched, and is available as control
`input for devices (not shown) being controlled by the
`touch pad assembly. The program is exited at 106. If it
`is determined at 100 that
`there is some number of
`
`45
`
`50
`
`55
`
`65
`
`'
`
`9
`
`

`

`5,189,417
`
`10
`
`l5
`
`20
`
`25
`
`3O
`
`35
`
`4s
`
`50
`
`55
`
`5
`switches greater than zero that are active, control
`passes to 108 where it is determined whether only one
`switch is active. If so, control passes to 110 where the
`identity of the active switch loaded into SWIDEN and
`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 SWIDEN and 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 40a—40d and,
`optionally, by comparators 480-48d. Because the coarse
`adjustment is made in hardware, the width of the pulse
`produced on lines 50a—50d may be made close to the
`window dictated by the width of the pulses produced
`by pulse drive circuit 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 allows all switches 28 to be moni-
`tored approximately every 4 milliseconds.
`While the invention is 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.
`We claim:
`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 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;
`‘
`at least one amplifier having an input connected at a
`given time to one of said sense lines, an output and
`gain means for establishing the gain of said 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-
`
`6
`parator means responsive at said given time to the
`amplified sensed signal of said one of said sense
`lines 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.
`2. The circuit in claim 1 wherein each of said gain
`means is independent of 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,
`each of 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 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
`means for 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 means for producing pulses
`having widths that are a function of the 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 of said 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 may be different from that for other
`comparator means.
`10. The circuit 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. The circuit 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. The circuit in claim 6 wherein said control circuit
`means includes means for establishing a reference pulse
`width associated with each of said touch pads and ad-
`justment means for adaptively adjusting each of said
`reference pulse width.
`13. A circuit for detecting user Contact of one of a
`plurality of touch pads comprising:
`
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`7
`a plurality of drive lines and a plurality of sense lines,
`each of 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 ampli-
`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 measurement to a reference pulse width; and
`multiplexing means for selectively connecting each
`said demodulating means to said control circuit
`means input.
`14. The circuit in claim 13 wherein each said demodu-
`lating means includes a comparator means responsive 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 level is individually selected for each of said de-
`modulating means.
`16. The circuit 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
`means includes 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 means in order to establish the touch pad associ-
`ated with each pulse.
`19. The circuit in claim 13 wherein said judging
`means includes means for establishing a reference pulse
`width associated with each of said touch pads and ad-
`
`8
`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,
`each of 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 connected to one of said sense lines, 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 means establishing a ref-
`erence level, wherein said comparator output is in
`a given state whenever the signal to the input is
`greater than the reference level 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 independent of the
`other said reference levels.
`.
`22. The circuit in claim 20 wherein each of said gain
`means is 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 means in order to establish the
`touch pad associated with each pulse.
`24. The circuit in claim 20 wherein said judging
`means includes means for establishing 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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