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1. (WO1992010823) TOUCH SENSOR AND CONTROLLER
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What is claimed:

1. A touch sensor for detecting the total force and die force-weighted average position of external forces applied to die surface of the touch sensor within a sensing zone extending over an X dimension and over a Y dimension, comprising:
(a) an X substrate that is an electrical insulator whereby the X substrate forms a first outer surface of the touch sensor;
(b) a plurality of X conductor traces deposited on the X substrate, distributed over the X dimension and extending along the Y dimension;
(c) an X fixed resistor deposited on the X substrate and connected to each of the X conductor traces for establishing a resistive path between adjacent X conductor traces;
(d) two X terminals connected to eitiier end of die X fixed resistor for interfacing the X fixed resistor to external circuitry;
(e) a Y substrate that is an electrical insulator positioned in facing relationship to the X substrate whereby the Y substrate forms a second outer surface of the touch sensor,
(f) a plurality of Y conductor traces deposited on die Y substrate, distributed over the Y dimension and extending along the X dimension;
(g) a Y fixed resistor deposited on the Y substrate and connected to each of d e Y conductor traces for establishing a resistive path between adjacent Y conductor traces;
(h) two Y terminals connected to eitiier end of die Y fixed resistor for interfacing the Y fixed resistor to external circuitry;
(i) a force variable resistor positioned between the X substrate and the Y substrate and having an electrical resistance that changes as a continuous function of the force applied thereto.

2. A touch sensor as recited in claim 1, wherein the force variable resistor comprises: (a) a plurality of X force variable resistor traces, each X force variable resistor trace deposited over an X conductor trace; and (b) a plurality of Y force variable resistor traces, each Y force variable resistor trace deposited over a Y conductor trace.

3. A touch sensor as recited in claim 2, further comprising:
(a) a plurality of X insulating traces deposited on die X substrate, each X insulating trace positioned between two adjacent X force variable resistor traces; and
(b) a plurality of Y insulating traces deposited on the Y substrate, each Y insulating trace positioned between two adjacent Y force variable resistor traces; whereby the X insulating traces and die Y insulating traces prevent the X force variable resistor traces from contacting the Y force variable resistor traces when there are no external forces applied to die sensing zone.

4. A touch sensor as recited in claim 1, wherein the force variable resistor comprises: (a) an X force variable resistor film deposited over the set of X conductor traces; and
(b) a Y force variable resistor film deposited over die set of Y conductor traces.

5. A touch sensor as recited in claim 4, further comprising:
(a) a plurality of X insulating dots, deposited on and distributed over die surface of the X force variable resistor, and
(b) a plurality of Y insulating dots, deposited on and distributed over the surface of the Y force variable resistor, whereby the X insulating dots and die Y insulating dots prevent the X force variable resistor film from contacting the Y force variable resistor film when there are no external forces applied to die sensing zone.

6. A touch sensor as recited in claim 1, wherein the force variable resistor is implemented by d e X fixed resistor and by die Y fixed resistor, whereby the X fixed resistor and die Y fixed resistor have a fixed resistance within the plane parallel to the substrates and a force variable resistance perpendicular to the plane of the substrates.

7. A touch sensor as recited in claim 1, further comprising an insulating spacer positioned between the X substrate and die Y substrate and extending around die periphery of die sensing zone, whereby the insulating spacer separates the X substrate from the Y substrate and relieves tension between the X substrate and the Y substrate when there are no external forces applied to the sensing zone.

8. A touch sensor as recited in claim 1, further comprising at least one additional X terminal connected to a midpoint along the X fixed resistor for dividing die X dimension into distinct X touch zones thereby allowing the detection of multiple touch points.

9. A touch controller for measuring and reporting the total force and the
force-weighted average position of extemal forces applied to a touch sensor, comprising:
(a) a touch sensor as recited in claim 1;
(b) a current regulator electrically connected to the touch sensor for maintaining a prescribed current through the touch sensor,
(c) at least one differential amplifier electrically connected to die touch sensor for measuring resistance values within the sensor,
(d) an X output signal that varies as a function of the force-weighted average position along the X dimension;
(e) a Y output signal tiiat varies as a function of the force-weighted average position along the Y dimension; and
(f) a Z output signal that varies as a function of the total of extemal forces applied to the touch sensor.

10. A touch controller as recited in claim 9, having an X differential amplifier
electrically connected to die X terminals for amplifying the differential voltage
across the X fixed resistor, the output of the X differential amplifier being the X
output signal; having a Y differential amplifier electrically connected to die Y

5 terminals for amplifying the differential voltage across the Y fixed resistor, d e
output of the Y differential amplifier being the Y output signal; and having a Z
differential amplifier electrically connected to one of the X terminals and
electrically connected to one of d e Y terminals for amplifying the voltage
differential across the force variable resistor, the output of the Z differential 10 amplifier being the Z output signal.

11. A touch controller as recited in claim 9, wherein die output of the current regulator is the Z output signal.

15 12. A touch controller as recited in claim 9, further comprising:
(a) a pair of X bridge resistors electrically connected to die X terminals, thereby forming a Wheatstone Bridge witii d e X fixed resistor for balancing the current
flowing through the X fixed resistor, and
(b) a pair of Y bridge resistors electrically connected to the Y terminals, thereby 0 forming a Wheatstone Bridge witii the Y fixed resistor for balancing the current
flowing through the Y fixed resistor.

13. A touch controller as recited in claim 9, further comprising:
(a) an X current mirror electrically connected to die X terminals for regulating 5 equal currents through each X terminal; and
(b) a Y current mirror electrically connected to the Y terminals for regulating equal currents through each Y terminal.

14. A touch controller as recited in claim 9, further comprising:
0 (a) an X common mode amplifier electrically connected to the X terminals for amplifying the common mode voltage across the X fixed resistor;

(b) a Y common mode amplifier electrically connected to the Y terminals for amplifying the common mode voltage across the Y fixed resistor; and
(c) a differential amplifier electrically connected to the output of the X common mode amplifier and to die output of the Y common mode amplifier, the output of the differential amplifier being the Z output signal.

15. A touch controller as recited in claim 9, further comprising at least one analog signal multiplexer for switching the current regulator between the X terminals and the Y terminals thereby permitting measurement of the resistance of the X fixed resistor and the resistance of the Y fixed resistor for calibration of the touch controller.

16. A touch controller as recited in claim 9, further comprising at least one analog signal switch for connecting one of the X terminals with one of the Y terminals thereby permitting measurement of the resistance of the X fixed resistor and the resistance of the Y fixed resistor for calibration of the touch controller.

17. A touch controller as recited in claim 9, having only one differential amplifier and further comprising:
(a) a first analog signal multiplexer for switching the inputs of the differential amplifier between the X terminals and the Y terminals; and
(b) a second analog signal multiplexer for switching the current regulator between the X terminals and die Y terminals; whereby the differential amplifier outputs the X output signal, the Y output signal, and the Z output signal, in a time multiplexed fashion.

18. A touch controller for measuring and reporting the total force and the
force-weighted average position of extemal forces applied to a touch sensor, comprising:
(a) a touch sensor as recited in claim 1;

(b) a plurahty of analog switches electrically connected to the touch sensor for interfacing the touch sensor to electronic measurement circuits;
(c) a voltage regulator electrically connected to die analog switches for
maintaining a prescribed voltage across the touch sensor,
(d) a current source electrically connected to the analog switches for measuring the force variable resistor,
(e) an amplifier electrically connected to die analog switches for detecting voltages representing the total force and die force-weighted average position;
(f) an X output signal that varies as a function of the force-weighted average position along the X dimension;
(g) a Y output signal that varies as a function of the force-weighted average position along the Y dimension; and
(h) a Z output signal that varies as a function of the total of extemal forces applied to die touch sensor.