SAR ADC with dynamic input scaling and offset adjustment

• US 8,035,622 B2
• Filed: 03/27/2008
• Issued: 10/11/2011
• 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): Mengistu; Amare
• Assistant Examiner(s): Sharifi-Tafreshi; Koosha
• Application Number:
  US12/057,262
• Publication Number:
  US 20090244014A1
• Time in Patent Office: 1,293 Days
• Field of Search: 345173-178, 341/126, 341/155, 341/158, 341/164
• 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 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.

2. The apparatus of claim 1, wherein the one or more receive channels form part of a single multi-touch subsystem for processing touch events.

3. The apparatus of claim 2, 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.

4. The apparatus of claim 1, wherein the SAR ADC comprises a charge redistribution capacitor array.

5. The apparatus of claim 4, wherein the SAR ADC comprises a scaling capacitor configurable for scaling a dynamic input range of the SAR ADC.

6. The apparatus of claim 4, 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.

7. The apparatus of claim 6, wherein the first and second capacitors are adjustable.

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

9. The apparatus of claim 6, wherein the offset is a function of the ratio of capacitances between the first capacitor and the second capacitor.

10. 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.

11. The apparatus of claim 10, 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.

12. The apparatus of claim 1, further comprising a trackpad that incorporates the touch panel.

13. The apparatus of claim 1, further comprising a touch sensitive display screen that incorporates the touch panel.