SAR ADC with dynamic input scaling and offset adjustment

• US 9,013,442 B2
• Filed: 07/20/2011
• Issued: 04/21/2015
• Est. Priority Date: 03/27/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hotelling, Steve Porter, Krah, Christoph Horst
• Primary Examiner(s): Sharifi-Tafreshi, Koosha
• Application Number:
  US13/187,433
• Publication Number:
  US 20110273402A1
• Time in Patent Office: 1,371 Days
• Field of Search: 345173-178, 341/126, 341/155, 341/158, 341/164, 178 1801- 1811
• US Class Current: 345/174
• 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 touch events, comprising:

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

wherein at least one receive channel includes a charge redistribution successive approximation register (SAR) analog to digital converter (ADC) with a dynamic input range;

wherein the dynamic input range of the SAR ADC is made up of a dynamic input range top end voltage and a dynamic input range bottom end voltage; and

wherein at least one charge redistribution SAR ADC includes a first capacitor and a second capacitor, the first and second capacitors configurable for i) scaling the 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.

2. The apparatus of claim 1, wherein the first and second capacitors are adjustable.

3. The apparatus of claim 2, wherein scaling of the dynamic input range is a function of a sum of capacitance values of the first capacitor and the second capacitor.

4. The apparatus of claim 2, wherein the offset is a function of a ratio of capacitance values of the first capacitor and the second capacitor.

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

a touch surface including the one or more touch sensors;

a touch subsystem couplable to the one or more touch sensors;

a touch panel processor coupled to the touch subsystem; and

a host processor coupled to the touch panel processor.

6. The apparatus of claim 5, further comprising a mobile telephone that incorporates the computing system.

7. The apparatus of claim 5, further comprising a personal computer that incorporates the computing system.

8. The apparatus of claim 5, further comprising a trackpad that includes the touch surface.

9. The apparatus of claim 5, further comprising a display screen that includes the touch surface.

10. 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 a touch surface at about the same time.

11. An apparatus for detecting touch events, comprising:

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

wherein at least one receive channel includes a charge redistribution successive approximation register (SAR) analog to digital converter (ADC) with a dynamic input range and operable in sampling and conversion stages;

wherein the dynamic input range of the SAR ADC is made up of a dynamic input range top end voltage and a dynamic input range bottom end voltage;

wherein at least one of the charge redistribution SAR ADCs comprise a first capacitor and a second capacitor, the first and second capacitors configurable for offsetting the dynamic input range by coupling at least one of the first and second capacitors to the dynamic input range top end voltage during the conversion stage; and

wherein the first and second capacitors are further configurable for scaling a dynamic input range of the SAR ADC by summing the capacitance values of the first capacitor and the second capacitor.

12. The apparatus of claim 11, wherein the first and second capacitors are adjustable.

13. The apparatus of claim 11, wherein the offset is a function of a ratio of capacitance values of the first capacitor and the second capacitor.

14. The apparatus of claim 11, further comprising a computing system that incorporates the apparatus, the computing system comprising:

a touch surface including the one or more touch sensors;

a touch subsystem couplable to the one or more touch sensors;

a touch panel processor coupled to the touch subsystem; and

a host processor coupled to the touch panel processor.

15. The apparatus of claim 14, further comprising a mobile telephone that incorporates the computing system.

16. The apparatus of claim 14, further comprising a personal computer that incorporates the computing system.

17. The apparatus of claim 14, further comprising a trackpad that includes the touch surface.

18. The apparatus of claim 14, further comprising a display screen that includes the touch surface.

19. The apparatus of claim 11, wherein the one or more receive channels are configurable for generating distinct values of multiple touch events occurring at distinct locations on or near a touch surface at about the same time.

29. The apparatus of claim 15, 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.

20. A 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 scan one or more rows of touch sensors in a touch panel by driving the one or more rows with the input stimulus; and

one or more receive channels, each receive channel couplable to a column of touch sensors in the touch panel, at least one receive channel comprising a charge redistribution successive approximation register (SAR) analog to digital converter (ADC) having an array of binary-weighted capacitors and 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 the charge redistribution SAR ADC includes a dynamic input range;

wherein the dynamic input range is made up of a dynamic input range top end voltage and a dynamic input range bottom end voltage; and

wherein at least one charge redistribution SAR ADC includes a first capacitor and a second capacitor, the first and second capacitors configurable for i) scaling the 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. 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;

during each touch panel row scan, coupling the columns of the touch panel to one or more receive channels;

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 by converting an analog waveform into a digital representation via a binary search implemented by a charge redistribution successive approximation register (SAR) analog to digital converter (ADC) with a dynamic input range made up of a dynamic input range top end voltage and a dynamic input range bottom end voltage;

offsetting the dynamic input range of the SAR ADC by shifting the dynamic input range using one or more capacitances in the charge redistribution SAR ADC; and

scaling the dynamic input range of the charge redistribution SAR ADC using the one or more capacitances.

22. A method for generating an image of touch on or about a touch-sensitive surface, comprising:

detecting one or more touch events;

generating values representative of detected touch events utilizing a successive approximation register analog to digital converter (SAR ADC) operable in sampling and conversion stages to convert an analog waveform representative of a touch event into a digital representation using a binary search, wherein a dynamic input range of the SAR ADC is made up of a dynamic input range top end voltage and a dynamic input range bottom end voltage;

offsetting the dynamic input range of the of the SAR ADC by coupling at least one of first and second capacitances of the SAR ADC to the dynamic input range top end voltage during the conversion stage; and

scaling the dynamic input range of the charge redistribution SAR ADC utilizing at least one of the first and second capacitances.

23. The method of claim 22, further comprising driving the touch-sensitive surface with a stimulus for enabling the detection of touch events.

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

25. The apparatus of claim 22, wherein the offset is a function of the ratio of the first and second capacitances.

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

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.

27. The apparatus of claim 26, wherein the SAR ADC comprises a charge redistribution capacitor array.

28. The apparatus of claim 26, wherein the SAR ADC comprises a scaling capacitor configurable for scaling a dynamic input range of the SAR ADC.