Touch sensitive device using threshold voltage signal

• US 8,773,366 B2
• Filed: 11/16/2009
• Issued: 07/08/2014
• Est. Priority Date: 11/16/2009
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hable, Brock A., Weaver, Billy Lee
• Primary Examiner(s): HALEY, JOSEPH R
• Application Number:
  US12/618,874
• Publication Number:
  US 20110115717A1
• Time in Patent Office: 1,695 Days
• Field of Search: None
• US Class Current: 345/173
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A touch sensitive apparatus having a plurality of drive electrodes and a plurality of receive electrodes, the drive electrodes and receive electrodes capacitively coupled to each other. A touch measurement circuit configured to identify touch events on the touch sensitive device by comparing a first time period to a second time period. The first time period can be, for example, representative of a length of time a periodic receive signal carried by a receive electrode is above or below a threshold voltage level.

Claims

1. A touch sensitive apparatus, comprising:

a touch sensitive device having a plurality of drive electrodes and a plurality of receive electrodes, wherein the drive electrodes are capacitively coupled to the receive electrodes; and

a touch measurement circuit configured to identify, in response to changes in capacitance via signals carried by the receive electrodes, one or more temporally overlapping touch events on the touch sensitive device, the touch measurement circuit further configured to;

receive a periodic receive signal carried by at least one of the receive electrodes,

receive a triangular periodic threshold signal having a frequency that is an integer multiple of a frequency of the periodic receive signal,

compare the periodic receive signal to the triangular periodic threshold signal during a sampling window,

determine a length of time during the sampling window that the periodic receive signal amplitude satisfies the threshold signal amplitude, and

identify a touch event based on the length of time that the periodic receive signal amplitude satisfies the threshold signal amplitude.

2. The touch sensitive apparatus of claim 1, wherein the drive electrodes are capacitively coupled to the receive electrodes by mutual capacitance, and further including

a signal drive circuit configured and arranged to apply a periodic drive signal to each of the plurality of drive electrodes;

and

wherein the touch measurement circuit further includes a logic circuit configured and arranged to determine the length of time, during each period of the drive signal, that the periodic receive signal amplitude satisfies the threshold signal amplitude

time duration, during each period of the drive signal, that the first signal amplitude exceeds the threshold signal level.

3. The touch sensitive apparatus of claim 1, further including a signal drive circuit configured and arranged to apply a drive signal with a frequency in the range of 20 kHz-1 MHz to at least one of the plurality of drive electrodes.

4. The touch sensitive apparatus of claim 3, wherein the periodic receive signal amplitude is determined by averaging a plurality of periodic receive signal amplitude samples.

5. The touch sensitive apparatus of claim 1, further including a signal drive circuit configured and arranged to apply a drive signal with a frequency in the range of 50 kHz-500 kHz to at least one of the plurality of drive electrodes.

6. The touch sensitive apparatus of claim 1, wherein the touch measurement circuit identifies a touch event by comparing the length of time that the periodic receive signal amplitude satisfies the threshold signal amplitude with a predetermined length of time indicative of a touch event.

7. The touch sensitive apparatus of claim 6, wherein the predetermined period of time includes a predetermined minimum period of time and a predetermined maximum period of time, wherein the predetermined minimum period of time and the predetermined maximum period of time are periodically updated.

8. The touch sensitive apparatus of claim 1, further comprising a signal drive circuit configured to sequentially apply a sinusoidal drive signal to each of the plurality of drive electrodes.

9. The touch sensitive apparatus of claim 8, wherein the signal drive circuit is further configured to, while applying the sinusoidal drive signal to a particular drive electrode, apply a fixed voltage to at least some of the plurality of drive electrodes that are other than the particular drive electrode.

10. The touch sensitive apparatus of claim 8, wherein the signal drive circuit is further configured to drive the periodic drive signal at a frequency between 70 kHz and 150 kHz.

11. The touch sensitive apparatus of claim 8, wherein the signal drive circuit is further configured to drive the periodic drive signal at a frequency between 100 kHz and 1 MHz.

12. The touch sensitive apparatus of claim 1, wherein the touch measurement circuit includes a counter configured to determine the length of time that the periodic receive signal amplitude satisfies the threshold signal amplitude by counting a number of oscillations of the counter within a period of the sinusoidal drive signal in which the periodic receive signal is above or below the threshold signal level.

13. A method of measuring mutual capacitances in a touch sensitive device having a plurality of drive electrodes and a plurality of receive electrodes, the method comprising:

applying a periodic drive signal to at least one of the drive electrodes for coupling, by mutual capacitance, to at least two of the receive electrodes;

receiving a periodic receive signal carried by at least one of the receive electrodes;

receiving a triangular periodic threshold signal having a frequency that is an integer multiple of a frequency of the periodic receive signal;

comparing the periodic receive signal to the triangular periodic threshold signal during a measurement cycle;

determining a length of time during the measurement cycle that the periodic receive signal amplitude satisfies the threshold signal amplitude; and

identifying a touch event based on the length of time that the periodic receive signal amplitude satisfies the threshold signal amplitude.

14. The method of claim 13, further including

applying a periodic drive signal to each of the plurality of drive electrodes;

and

determining the length of time during the sampling window that the periodic receive signal amplitude satisfies the threshold signal amplitude, wherein the measurement cycle is defined based on a period of the drive signal.

15. The method of claim 13, further comprising amplifying the periodic receive signal, and further including applying a drive signal with a frequency in the range of 20 kHz-1 MHz to at least one of the plurality of drive electrodes.

16. The method of claim 13, further including applying a drive signal with a frequency in the range of 50 kHz-500 kHz to at least one of the plurality of drive electrodes.

17. The method of claim 16, wherein the periodic receive signal amplitude is determined by averaging a plurality of periodic receive signal amplitude samples.

18. The method of claim 13, wherein the determining step comprises counting a number of oscillations of a counter within a period of the periodic drive signal in which the periodic receive signal satisfies the threshold signal level.

19. The method of claim 13, wherein the identifying step further comprises comparing the length of time to a predetermined length of time associated with an absence of a touch event to the touch sensitive device.

20. The method of claim 13, wherein the applying step further comprises applying a ground voltage level to each of the plurality of drive electrodes to which the periodic drive signal is not currently being applied.

21. An apparatus comprising:

at least one circuit configured to detect the presence of an object in proximity to a first and a second electrode, the first electrode driven with a periodic voltage signal, and the second electrode carrying a periodic voltage signal resulting from the voltage signal on the first electrode capacitively coupling to the second electrode,

the presence of the object detected by comparing the periodic voltage signal to a triangular periodic threshold signal, determining a length of time during the sampling window that the periodic receive signal amplitude satisfies the threshold signal amplitude, and detecting presence of the object based on the length of time that the periodic receive signal amplitude satisfies the threshold signal amplitude.

22. The apparatus of claim 21, further including

a signal drive circuit configured and arranged to apply a periodic drive signal to each of the plurality of drive electrodes.

23. The apparatus of claim 21, further comprising amplifying the periodic voltage signal carried on the second electrode.

24. The apparatus of claim 21, wherein determining the length of time includes, for a measurement cycle, counting a number of oscillations of a counter during which the periodic receive signal is above the threshold signal level, in response to the threshold signal level being positive, or below the threshold signal level, in response to the threshold signal level being negative, wherein the measurement cycle includes one or more periods of the periodic voltage signal.

25. A touch sensitive apparatus, comprising:

a touch sensitive device having a plurality of drive electrodes and a plurality of receive electrodes, wherein the drive electrodes are capacitively coupled to the receive electrodes; and

a touch measurement circuit configured to identify, in response to changes in capacitance via signals carried by the receive electrodes, one or more temporally overlapping touch events on the touch sensitive device, the touch measurement circuit further comprising;

a receive circuit including a first amplifier having an inverting input connected to receive a periodic receive signal carried by at least one of the receive electrodes, the receive circuit further including a second amplifier having an inverting input connected to receive an output of the first amplifier and a non-inverting input connected to receive a threshold signal and that generates a periodic square wave output, the receive circuit further including a logic circuit that receives the periodic square wave output of the second amplifier and determines a length of time during a sampling window that an amplitude of the periodic receive signal amplitude satisfies the threshold signal amplitude based on the periodic square wave output; and

a processing unit that identifies a touch event based on the length of time that the periodic receive signal amplitude satisfies the threshold signal amplitude.