Using Capacitive Proximity Detection with Resistive Touch Screens for Wake-Up

• US 20140253500A1
• Filed: 02/17/2014
• Published: 09/11/2014
• Est. Priority Date: 03/08/2013
• Status: Active Application

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Curtis, Keith E.
• Granted Patent: US 10,254,815 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 1/3215 Monitoring of peripheral devices
• CPC Class Codes: G06F 1/3231 Monitoring the presence, absence or movement of users
• CPC Class Codes: G06F 1/3262 Power saving in digitizer or tablet
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

Power consumption of a device having a resistive touch screen may be reduced if the resistive touch screen is not scanned unless a touch thereto is imminent, especially if the device can remain in a low power sleep mode during no-touch inactivity. Furthermore, detecting a potential touch earlier then an actual first touch may improve initial touch response time. The resistive touch screen may comprise top and bottom Indium Tin Oxide (ITO) coated planes. The top ITO coated plane may be used as a capacitive proximity detector and the bottom ITO coated plane may be used as a guard shield for the top ITO coated plane to significantly reduce parasitic capacitance thereof and enhance the sensitivity of capacitive proximity detection. The device may also remain in a low power sleep mode until a potential touch is detected thereby further saving device power consumption.

Claims

1. An apparatus having a capacitive proximity detector and a resistive touch screen, comprising:

a first conductive plane having a resistance between opposite edges thereof;

a second conductive plane having a resistance between opposite edges thereof and located parallel with the first conductive plane;

a first pair of tri-state drivers, wherein an output from one of the first pair is coupled to an edge of the first conductive plane and an output from the other one of the first pair is coupled to an opposite edge of the first conductive plane;

a second pair of tri-state drivers, wherein an output from one of the second pair is coupled to an edge of the second conductive plane and an output from the other one of the second pair is coupled to an opposite edge of the second conductive plane;

wherein the coupled edges of the first conductive plane are substantially perpendicular to the coupled edges of the second conductive plane;

a multiplexer having inputs coupled to respective ones of the edges of the first and second conductive planes;

an analog-to-digital converter (ADC) having an analog input coupled to an output of the multiplexer;

a capacitance measurement circuit coupled to one of the edges of the first conductive plane; and

a digital processor having digital outputs coupled to signal and tri-state control inputs of the first and second pairs of tri-state drivers, a multiplexer control output coupled to the multiplexer, at least one input and at least one output coupled to the capacitance measurement circuit, and at least one digital input coupled to at least one digital output of the ADC;

wherein

the digital processor charges the first conductive plane to a first voltage with at least one of the first pair of tri-state drivers,

the first conductive plane is coupled to the capacitance measurement circuit and the analog input of the ADC through the multiplexer,

the capacitance measurement circuit modifies the first voltage on the first conductive plane,

the ADC samples the modified first voltage and provides a digital representation thereof to the digital processor;

the digital processor determines whether a change in the modified first voltage indicates an object proximate to an outward face of the first conductive plane; and

if the object is determined to be proximate to the outward face of the first conductive plane then the digital processor uses the first and second tri-state drivers to configure the first and second conductive planes into a resistive touch screen.

2. The apparatus according to claim 1, wherein the modified first voltage represents a capacitance of the first conductive plane.

3. The apparatus according to claim 1, wherein the capacitance measurement circuit comprises a capacitive voltage divider (CVD) circuit.

4. The apparatus according to claim 1, wherein the capacitance measurement circuit comprises a charge time measurement unit (CTMU) circuit.

5. The apparatus according to claim 1, wherein the first conductive plane is a flexible substrate coated with Indium Tin Oxide (ITO).

6. The apparatus according to claim 5, wherein the first conductive plane is substantially transparent.

7. The apparatus according to claim 5, wherein the second conductive plane is coated with Indium Tin Oxide (ITO) and the ITO coatings of the first and second conductive planes face each other, whereby when a touch is applied to the face of the first conductive plane the ITO coatings between the first and second conductive planes make contact at a location of the touch and the digital processor thereby determines the touch location.

8. The apparatus according to claim 1, wherein the digital processor charges the second conductive plane to the first voltage with at least one of the second pair of tri-state drivers.

9. The apparatus according to claim 1, wherein the first and second pairs of tri-state drivers, the multiplexer, the ADC, the capacitance measurement circuit and the digital processor are provided in a microcontroller integrated circuit.

10. The apparatus according to claim 9, wherein the microcontroller integrated circuit has a low power sleep mode that periodically wakes up sufficient circuits therein to determine whether an object is proximate to the outward face of the first conductive plane.

11. The apparatus according to claim 1, wherein the object comprises a fingertip of a user.

12. The apparatus according to claim 1, wherein the first voltage is at substantially a power supply voltage.

13. The apparatus according to claim 1, wherein the first voltage is at substantially a power supply common.

14. A method for determining whether an object is proximate to a resistive touch screen and thereafter enabling the resistive touch screen for determining touches thereto, said method comprising the steps of:

charging a first conductive plane to a first voltage;

coupling the charged first conductive plane to a capacitance measurement circuit;

modifying the first voltage on the first conductive plane with the capacitance measurement circuit;

measuring the modified first voltage;

determining from the measured modified first voltage whether an object is proximate to the first conductive plane;

reconfiguring the first conductive plane and a second conductive plane parallel to the first conductive plane into a resistive touch screen when the object has been determined to be proximate to the first conductive plane; and

scanning the first and second conductive planes to determine where a touch is applied thereto.

15. The method according to claim 14, further comprising the step of charging the conductive plane to the first voltage after the step of charging the first conductive plane to the first voltage.

16. The method according to claim 14, further comprising the step of maintaining a low power sleep mode and periodically waking up from the low power sleep mode to detect the object proximate to the top conductive plane.

17. The method according to claim 14, wherein the he first conductive plane is a flexible substrate coated with Indium Tin Oxide (ITO).

18. The method according to claim 14, wherein the second conductive plane is coated with Indium Tin Oxide (ITO) and the ITO coatings of the first and second conductive planes face each other, whereby when the touch is applied to the face of the first conductive plane the ITO coatings between the first and second conductive planes make contact at where the touch is applied thereto and a touch location is thereby determined.

19. A method for determining whether an object is proximate to a resistive touch screen and thereafter enabling the resistive touch screen for determining touches thereto, said method comprising the steps of:

determining whether an object is proximate to a face of a first substrate in parallel with an located over a second substrate;

scanning the first and second substrates when the object has been determined to be proximate to the face of the first substrate;

detecting a touch to the face of the first substrate; and

determining a location of the touch on the face of the first substrate.

20. The method according to claim 19, wherein the steps of detecting the touch and determining the location are done through a resistive touch screen.