SAR ADC WITH DYNAMIC INPUT SCALING AND OFFSET ADJUSTMENT

• US 20090244014A1
• Filed: 03/27/2008
• Published: 10/01/2009
• Est. Priority Date: 03/27/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: HOTELLING, Steve Porter, Krah, Christoph Horst
• Granted Patent: US 8,035,622 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/04106 Multi-sensing digitiser, i.e. digitiser using at least two different sensing technologies simultaneously or alternatively, e.g. for detecting pen and finger, for saving power or for improving position detection
• 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 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G06F 3/05 Digital input using the sampling of an analogue quantity at regular intervals of time , input from a/d converter or output to d/a converter

Abstract

An apparatus for generating an image of touch on or about a touch-sensitive surface comprising a touch panel is disclosed. The touch panel can include a plurality of touch sensors configured for detecting one or more touch events occurring at distinct locations at about the same time. Each touch event can comprise a touching of an object against the touch-sensitive surface. A plurality of receive channels can be coupled to the touch panel for generating values representative of detected touch events. The receive channels can include a charge redistribution successive approximation register digital-to-analog converter (SAR ADC) configured to convert an analog waveform into a digital representation via a binary search and outputting the digital representation to an output register. The SAR ADC architecture can be such that it the dynamic input range can be scaled and offset adjusted.

Claims

1. An apparatus for detecting multi-touch events with a touch-sensitive surface, comprising:

a plurality of touch sensors configured for detecting one or more touch events at or near the touch-sensitive surface; and

one or more receive channels couplable to the plurality of touch sensors, the one or more receive channels configurable for generating distinct values representative of the detected one or more touch events by converting inputted analog waveforms into respective digital representations using a binary search.

2. The apparatus of claim 1, wherein the one or more receive channels each comprise a charge redistribution successive approximation register (SAR) analog to digital converter (ADC).

3. The apparatus of claim 2, wherein each of the charge redistribution SAR ADCs comprise a scaling capacitor configurable for scaling a dynamic input range of the SAR ADC.

4. The apparatus of claim 2, wherein each of the charge redistribution SAR ADCs comprise a first capacitor and a second capacitor, the first and second capacitors configurable for i) scaling a dynamic input range of the SAR ADC;

and ii) offsetting the dynamic input range by shifting the dynamic input range relative to a reference voltage.

5. The apparatus of claim 4, wherein the first and second capacitors are adjustable.

6. The apparatus of claim 5, wherein scaling of the dynamic input range is a function of a sum of capacitance values of the first capacitor and the second capacitor.

7. The apparatus of claim 5, wherein the offset is a function of a ratio of capacitance values of the first capacitor and the second capacitor.

8. The apparatus of claim 1, further comprising a computing system that incorporates the apparatus, the computing system comprising:

a multi-touch subsystem couplable to the plurality of touch sensors;

a multi-touch panel processor coupled to the multi-touch system; and

a host processor coupled to the multi-touch panel processor.

9. The apparatus of claim 8, further comprising a mobile telephone that incorporates the computing system.

10. The apparatus of claim 8, further comprising a digital audio player that incorporates the computing system.

11. The apparatus of claim 8, further comprising a personal computer that incorporates the computing system.

12. The apparatus of claim 11, further comprising a trackpad that includes the multi-touch surface.

13. The apparatus of claim 11, further comprising a display screen that includes the multi-touch surface.

14. The apparatus of claim 1, wherein the one or more receive channels are configurable for generating distinct values of multiple touch events occurring at distinct locations on or near the touch sensitive surface at about the same time.

15. An apparatus for generating an image of touch on or about a touch-sensitive surface, comprising:

a touch panel, the touch panel including a plurality of touch sensors configured for detecting one or more touch events; and

a plurality of receive channels couplable to the touch panel for generating values representative of detected touch events, at least some of the plurality of receive channels comprising;

(i) a charge amplifier connectable to the multi-touch panel;

(ii) an anti-aliasing filter connectable to the charge amplifier; and

(iii) a successive approximation register digital-to-analog converter (SAR ADC) connectable to the anti-aliasing filter, the SAR ADC configurable to convert an analog waveform into a digital representation using a binary search and outputting the digital representation to an output register.

16. The apparatus of claim 15, wherein the one or more receive channels form part of a single multi-touch subsystem for processing touch events.

17. The apparatus of claim 16, the multi-touch subsystem comprising driver logic couplable to the touch panel and configured for driving the touch panel with a stimulus for enabling a detection of touch events.

18. The apparatus of claim 15, wherein the SAR ADC comprises a charge redistribution capacitor array.

19. The apparatus of claim 18, wherein the SAR ADC comprises a scaling capacitor configurable for scaling a dynamic input range of the SAR ADC.

20. The apparatus of claim 18, wherein the SAR ADC comprises a first capacitor and a second capacitor, the first and second capacitors configurable for i) scaling a dynamic input range of the SAR ADC;

and ii) offsetting the dynamic input range by shifting the dynamic input range relative to a reference voltage.

21. The apparatus of claim 20, wherein the first and second capacitors are adjustable.

22. The apparatus of claim 20, wherein scaling of the dynamic input range is a function of the sum of the capacitances of the first capacitor and the second capacitor.

23. The apparatus of claim 20, wherein the offset is a function of the ratio of capacitances the first capacitor and the second capacitor.

24. The apparatus of claim 15, further comprising a computing system that incorporates the apparatus, the computing system comprising:

a multi-touch subsystem couplable to the plurality of touch sensors;

a multi-touch panel processor coupled to the multi-touch system; and

a host processor coupled to the multi-touch panel processor.

25. The apparatus of claim 24, further comprising one of:

(i) a mobile telephone that incorporates the computing system;

(ii). a digital audio player that incorporates the computing system;

or (iii) a personal computer that incorporates the computing system.

26. The apparatus of claim 15, further comprising a trackpad that incorporates the touch panel.

27. The apparatus of claim 15, further comprising a touch sensitive display screen that incorporates the touch panel.

28. A multi-touch subsystem for detecting touch events on or about a touch-sensitive surface and generating an image of touch, comprising:

driver logic configured for generating an input stimulus;

channel scan logic configured for controlling the driver logic to sequentially scan each row of touch sensors in a touch panel, and to sequentially scan each row of proximity sensors in a proximity sensor panel, by sequentially driving each row with the input stimulus; and

one or more receive channels, each receive channel couplable to a column of touch sensors in the touch panel or a column of proximity sensors in the proximity sensor panel, each receive channel comprising a charge redistribution SAR ADC configured for receiving a signal representative of a touch event occurring at one of the touch sensors in the column of touch sensors and generating a digital value representative of the touch event via a binary search,

wherein scanning one or more rows in the touch panel enables a detection of multiple touch events occurring at distinct locations at about the same time.

29. A method for detecting touch events on or about a touch-sensitive surface, comprising:

scanning a touch panel of touch sensors organized in rows and columns by sequentially applying a first stimulus to each row; and

during each touch panel row scan, coupling the columns of the touch panel to one or more receive channels and generating one or more digital values representative of one or more touch events occurring at distinct locations along the row at about the same time,

wherein generating the one or more digital values comprises converting an analog waveform into a digital representation via a binary search implemented by a charge redistribution SAR ADC.

30. The method of claim 29, further comprising:

(i) scaling an input range of the charge redistribution SAR ADC and (ii) offsetting the input range of the charge redistribution SAR ADC.