Waterproof baseline tracking in capacitive touch controllers

• US 8,823,678 B2
• Filed: 03/02/2012
• Issued: 09/02/2014
• Est. Priority Date: 01/09/2012
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Li, Tianhao, Sobel, David Amory, Joshi, Satish Vithal
• Primary Examiner(s): SHENG, TOM V
• Application Number:
  US13/410,844
• Publication Number:
  US 20130176268A1
• Time in Patent Office: 914 Days
• Field of Search: 345173-178, 178 1803- 1809, 178/18.11, 715/863, 715/864
• US Class Current: 345/174
• 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 3/04186 Touch location disambiguation
• CPC Class Codes: G06F 3/044 by capacitive means
• 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 method for a touch panel control circuit includes stimulating a touch panel and receiving signals responsive to the stimulating. Based on the received signals, water or another contaminant may be determined to be present on the touch panel. While the contaminant is present on the touch panel, a wet baseline mode of operation in which a different baseline value is used to detect a touch condition for the touch panel. When the contaminant is removed, operation returns to a dry baseline mode.

Claims

1. A method for a touch panel control circuit, the method comprising:

stimulating a touch panel;

receiving signals from the touch panel responsive to the stimulating;

based on the received signals, determining a contaminant to be present on the touch panel, including

comparing a minimum capacitance value for the touch panel with a threshold value, and

if the minimum capacitance value exceeds the threshold value,

determining the contaminant is present; and

switching to a wet baseline mode of operation while the contaminant is present on the touch panel.

2. The method of claim 1 further comprising:

filtering the received signals;

based on the received signals, determining a touch event has occurred on the touch panel by

using the received signals to determine pixel capacitance levels for pixels of the touch panel,

subtracting baseline capacitance levels from the pixel capacitance levels to determine detected capacitance levels, and

using the determined detected capacitance levels to determine that the touch event has occurred;

suspending the filtering of the received signal; and

processing the determined touch event.

3. The method of claim 2 wherein filtering the received signals comprises:

filtering the received signals in a relatively slow tracking filter.

4. The method of claim 2 further comprising:

establishing dry baseline capacitance levels for the touch panel;

based on the received signals, determining pixel capacitance levels for pixels of the touch panel;

in a dry baseline mode of operation, subtracting the dry baseline capacitance level from respective pixel capacitance levels to determine detected capacitance levels;

in the wet baseline mode of operation, subtracting wet baseline capacitance levels from the respective capacitance levels to determine the detected capacitance levels; and

determining the touch event has occurred based on the determined detected capacitance values.

5. The method of claim 1 wherein switching to a wet baseline mode of operation comprises:

filtering the received signals in a relatively slow tracking filter;

based on the received signals, determining an anti-touch event has occurred on the touch panel, including

detecting capacitance changes of a first polarity due to touch events on the touch panel,

detecting a capacitance change having a second polarity different from the first polarity, and

based on the capacitance change having a second polarity, determining the anti-touch even has occurred;

suspending the filtering of the received signal;

recalibrating wet baseline capacitance data for the touch panel; and

selecting wet baseline capacitance data for determining detected capacitance levels for pixels of the touch pad.

6. The method of claim 5 wherein recalibrating wet baseline data comprises measuring capacitance for the touch panel when no touch event occurs.

7. The method of claim 1 wherein determining a contaminant is present comprises:

after determining the contaminant is present, measuring a time period during which the minimum capacitance value exceeds the predetermined threshold value; and

when the time period exceeds a predetermined time threshold, recalibrating by determining new baseline capacitance data for the touch panel.

8. The method of claim 1 further comprising:

in response to the received signals, detecting an anomalous condition on the touch panel when a detected capacitance level change exceeds a maximum negative capacitance change threshold;

during a temporal processing period following an initialization of the touch panel control circuit, determining the anomalous condition corresponds to a corrupted baseline data;

recalibrating the baseline data;

following expiration of the temporal processing period, determining the anomalous condition corresponds to a contaminant present on the touch panel.

9. A controller circuit for a touch panel, the controller circuit comprising:

a baseline tracking filter having an input configured to receive raw signals from the touch panel upon electrical stimulation of the touch panel and a baseline output operative to provide baseline capacitance data for the touch panel;

a combiner having a first input coupled to the input to receive the raw signals and having a second input to receive the baseline output, and an output operative to provide capacitance heatmap data for the touch panel; and

a controller operatively coupled to the baseline filter to select one of a dry baseline mode and a wet baseline mode of operation based on the capacitance heat map data for the touch panel, the controller varying the bandwidth of the filter based on the mode of operation.

10. The controller circuit of claim 9 further comprising:

a data store to store dry baseline data upon selection of the wet baseline mode of operation, for subsequent retrieval upon selection of the dry baseline mode.

11. The controller circuit of claim 9 wherein the controller is configured to vary response of the filter based on rate of baseline capacitance variation detected for the touch panel.

12. The controller circuit of claim 11 wherein the controller is configured to disable the filter upon selection of the wet baseline mode of operation.

13. A method for a touch panel control circuit, the method comprising:

stimulating the touch panel with electrical signals;

detecting raw capacitance data for the touch panel in response to the stimulating;

subtracting a baseline level from the raw capacitance level to produce touch heat map data for the touch panel, including;

subtracting a dry baseline level to produce the touch heat map data, and

subtracting a wet baseline level to produce the touch heat map data when the raw capacitance data indicates an abnormal condition exists on the touch panel.

14. The method of claim 13 further comprising:

comparing the raw capacitance data to a touch threshold;

when the raw capacitance data exceeds the touch threshold for a predetermined time period, determining a touch event has occurred; and

subtracting the dry baseline level from the raw capacitance data to process the touch event for the touch panel.

15. The method of claim 13 further comprising:

comparing the raw capacitance data to an abnormal touch threshold;

when the raw capacitance data exceeds the abnormal touch threshold for a predetermined time period, determining an anti-touch event has occurred; and

subtracting the wet baseline level from the raw capacitance data to process the touch event.

16. The method of claim 15 further comprising:

upon detecting the anti-touch event, storing the dry baseline level;

using the wet baseline level to produce the touch heat map data for the touch panel while the anti-touch event continues; and

retrieving the stored dry baseline level when the anti-touch even no longer exists.

17. The method of claim 13 further comprising:

filtering the raw capacitance data in a low pass filter to produce a current baseline level.

18. The method of claim 17 further comprising:

reducing an update rate of filtering when no touch event and no abnormal condition exists on the touch panel; and

wherein reducing the update rate of filtering comprises decimating the raw capacitance data before filtering the raw capacitance data.

19. The method of claim 13 further comprising:

performing a baseline level recalibration procedure;

retrieving stored true baseline data; and

performing a spatial verification procedure between recalibrated baseline data and the true baseline data.