Touch sense using time domain reflectometry
First Claim
Patent Images
1. A method for sensing a touch to a substrate and determining a location thereof, said method comprising the steps of:
- providing a serpentine transmission line fabricated on a substrate comprising a plurality of touch locations having a first and second end;
unterminating a second end of the serpentine transmission line;
sending a first pulse to the first end of the serpentine transmission line;
charging a timing capacitor with a constant current source until a first touch return pulse is received at the first end of the serpentine transmission line;
measuring a first voltage on the timing capacitor;
converting the measured first voltage to a first location on the substrate;
unterminating the first end of the serpentine transmission line;
sending a second pulse to the second end of the serpentine transmission line;
charging the timing capacitor with the constant current source until a second touch return pulse is received at the second end of the serpentine transmission line;
measuring a second voltage on the timing capacitor; and
converting the measured second voltage to a second location on the substrate.
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Abstract
A touch panel or screen has a serpentine transmission line fabricated on a substrate, e.g., printed circuit board, LCD, plasma or LED screen, etc., and has a constant impedance. A touch to the touch panel will cause a change of impedance of the transmission line at the location of the touch. Time domain reflectometry (TDR) is used for determining the location of the change of impedance of the transmission line by accurately measuring the return pulse time at the source of the initial pulse, and then converting the return pulse time to X-Y coordinates of the touch panel or screen.
20 Citations
27 Claims
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1. A method for sensing a touch to a substrate and determining a location thereof, said method comprising the steps of:
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providing a serpentine transmission line fabricated on a substrate comprising a plurality of touch locations having a first and second end; unterminating a second end of the serpentine transmission line; sending a first pulse to the first end of the serpentine transmission line; charging a timing capacitor with a constant current source until a first touch return pulse is received at the first end of the serpentine transmission line; measuring a first voltage on the timing capacitor; converting the measured first voltage to a first location on the substrate; unterminating the first end of the serpentine transmission line; sending a second pulse to the second end of the serpentine transmission line; charging the timing capacitor with the constant current source until a second touch return pulse is received at the second end of the serpentine transmission line; measuring a second voltage on the timing capacitor; and converting the measured second voltage to a second location on the substrate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for sensing a touch to a substrate and determining a location thereof, said method comprising the steps of:
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a) initializing a time of a time measurement device; b) coupling a pulse driver to a first end of a serpentine transmission line fabricated on a substrate comprising a plurality of touch locations, wherein the serpentine transmission line is un-terminated at a second end thereof; c) start sending a pulse with the pulse driver at the first end of the serpentine transmission line; d) starting the time in the time measurement device; e) detecting whether a negative return pulse, caused by a touch on the substrate, is received at the first end of the serpentine transmission line, wherein if the negative return pulse is detected then going to step g), and if not then going to step f); f) detecting when a positive return pulse is received at the first end of the serpentine transmission line, the positive return pulse being from the un-terminated second end of the serpentine transmission line, wherein if the positive return pulse is detected then returning to step a), and if not then returning to step e); g) stopping the time in the time measurement device; h) reading the time from the time measurement device; and i) converting the time read from the time measurement device into a location of the touch on the substrate then returning to step a).
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17. An apparatus for sensing a touch to a substrate and determining a location thereof, comprising:
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a pulse generator for generating pulses; a first pulse driver having an input coupled to the pulse generator and an output coupled through a first resistor to a first end of a serpentine transmission line fabricated on a substrate, wherein the output of the first pulse driver can be controlled to be set into high impedance, a second pulse driver having an input coupled to the pulse generator and an output coupled through a second resistor to the second end of the serpentine transmission line, wherein the output of the second pulse driver can be controlled to be set into high impedance; wherein the first and second resistors each have resistances that are substantially equal to a characteristic impedance of the serpentine transmission line; a constant current source; a timing capacitor; an analog-to-digital converter (ADC); and a digital processor; wherein the digital processor controls the output of the second driver to be set in high impedance and wherein the pulse generator generates a first pulse to the first pulse driver which sends the first pulse to the first end of the serpentine transmission line, and then the constant current source starts charging the timing capacitor until a first return pulse is received at the first end of the serpentine transmission line; a first voltage charge on the timing capacitor is sampled by the ADC and converted to a first digital value; and the digital processor receives the first digital value from the ADC and converts the first digital value to a first location on the substrate. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 27)
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26. A method for sensing a touch to a substrate and determining a location thereof, said method comprising the steps of:
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sending a first pulse to a first end of a serpentine transmission line fabricated on a substrate comprising a plurality of touch locations while a second end of the transmission line is unterminated by switching an output of a driver into high impedance, wherein the output of the driver is coupled with the second end through a terminating resistor; charging a timing capacitor with a constant current source until a first touch return pulse is received at the first end of the serpentine transmission line; measuring a first voltage on the timing capacitor; and converting the measured first voltage to a first location on the substrate.
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Specification