SENSING UNIT, SENSING ARRANGEMENT AND SENSING METHOD FOR TOUCH PANEL APPLICATION

• US 20110267312A1
• Filed: 04/27/2011
• Published: 11/03/2011
• Est. Priority Date: 04/30/2010
• Status: Active Grant

• Current Assignee: Elan Microelectronics Corporation
• Original Assignee: Elan Microelectronics Corporation
• Inventors: HSU, SHIH-YUAN, HSU, WEN-JUN, TAO, YI-HSIN, LIN, CHIA-HSING, LEE, I-SHU
• Granted Patent: US 8,952,922 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 2203/04107 Shielding in digitiser, i.e. guard or shielding arrangements, mostly for capacitive touchscreens, e.g. driven shields, driven grounds
• 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

Two sensing units are configured as an exciter and a sensor connected to two trace lines, respectively, for mutual capacitance sensing from the capacitance units including these two trace lines. The two sensing units connect the two trace lines together to balance them to a same voltage level first, and then disconnect them from each other. Thereafter, the exciter connects the first trace line to an excitation node to induce a charge change on the second trace line, and the sensor senses the charge change to detect the variation of the mutual capacitance between the two trace lines.

Claims

1. A sensing arrangement for touch panel application, comprising:

a first sensing unit connected to a first trace line, operating with an exciter mode to apply a first charge current to the first trace line during an equalization phase, and then switch the first trace line to connect to an excitation node during an excitation phase;

a second sensing unit connected to a second trace line, operating with a sensor mode to apply a second charge current to the second trace line during the equalization phase and the excitation phase, and sense a charge change on the second trace line to apply a mirror current to an output node during the excitation phase; and

an equalization line switched to connect to the first and second trace lines during the equalization phase, and to disconnect from the first and second trace lines during the excitation phase.

2. The sensing arrangement of claim 1, wherein the excitation node is grounded.

3. The sensing arrangement of claim 1, wherein the second sensing unit comprises:

an equalization switch connected between the second trace line and the equalization line;

a current mirror operative to generate the second charge current and the mirror current; and

a sample switch connected between the current mirror and the output node.

4. The sensing arrangement of claim 3, further comprising an integrator connected to the output node for storing the mirror current so as to generate an output voltage.

5. The sensing arrangement of claim 4, wherein the integrator comprises a capacitor.

6. The sensing arrangement of claim 4, further comprising a reset switch connected to the output node for resetting the integrator.

7. The sensing arrangement of claim 3, wherein the second sensing unit further comprises:

a charge switch connected between the second trace line and the current mirror; and

a ground switch connected between the second trace line and a ground node.

8. The sensing arrangement of claim 1, wherein the first sensing unit comprises:

an equalization switch connected between the first trace line and the equalization line;

an excitation switch connected between the first trace line and the excitation node;

a current mirror operative to generate the first charge current; and

a charge switch connected between the first trace line and the current mirror.

9. The sensing arrangement of claim 1, wherein the first and second sensing units are located in two different sensing chips, respectively.

10. A sensing unit for touch panel application, comprising:

a switch arrangement connected to a trace line, operative to control an operational phase of the sensing unit;

a current mirror connected to the switch arrangement, controlled to apply a charge current to the trace line during an equalization phase when the sensing unit operates with either an exciter mode or a sensor mode, and to generate a mirror current depending on a charge change on the trace line when the sensing unit operates with the sensor mode; and

a sample switch connected between the current mirror and an output node, controlled to apply the mirror current to the output node during an excitation phase when the sensing unit operates with the sensor mode.

11. The sensing unit of claim 10, further comprising a reset switch connected to the output node for resetting a voltage on the output node.

12. The sensing unit of claim 10, wherein the switch arrangement comprises:

an equalization switch connected between the trace line and an equalization node;

an excitation switch connected between the trace line and an excitation node; and

a charge switch connected between the trace line and the current mirror.

13. The sensing unit of claim 12, wherein the switch arrangement further comprises a ground switch connected between the trace line and a ground node.

14. The sensing unit of claim 12, wherein the excitation node is grounded.

15. The sensing unit of claim 12, wherein the equalization switch is on to connect the trace line to the equalization node during the equalization phase.

16. The sensing unit of claim 12, wherein the excitation switch is on to connect the trace line to the excitation node when the sensing unit operates with a fixed-driven mode.

17. The sensing unit of claim 10, wherein the switch arrangement makes the trace line floating when the sensing unit operates with a non-driven mode.

18. A sensing method for touch panel application, comprising the steps of:

connecting a first trace line to a second trace line to balance the first and second trace lines to a same voltage level;

switching the first trace line to an excitation node when the first trace line is disconnected from the second trace line; and

sensing a charge change on the second trace line when the first trace line is connected with the excitation node.

19. The sensing method of claim 18, further comprising the steps of:

generating a mirror current depending on the sensed charge change; and

storing the mirror current to generate an output voltage.

20. A sensing method for touch panel application, comprising the steps of:

(A) defining a plurality of area partitions on a touch panel;

(B) sensing each of the plurality of area partitions when the touch panel is free of object to obtain and store a reference projected mutual capacitance for each of the plurality of area partitions;

(C) sensing each of the plurality of area partitions to obtain a projected mutual capacitance for each of the plurality of area partitions; and

(D) if a difference between the reference projected mutual capacitance and the projected mutual capacitance of any of the plurality of area partitions is larger than a threshold, performing a sub-area scan of this area partition to calculate an object location.

21. The sensing method of claim 20, wherein each adjacent two of the plurality of area partitions overlap mutually around a boundary therebetween.

22. The sensing method of claim 20, wherein the step B comprises the step of:

for sensing each of the plurality of area partitions, simultaneously exciting a trace line in a first direction of this area partition and detecting a trace line in a second direction of this area partition, to obtain the reference projected mutual capacitance of this area partition.

23. The sensing method of claim 20, wherein the step C comprises the step of:

for sensing each of the plurality of area partitions, simultaneously exciting a trace line in a first direction of this area partition and detecting a trace line in a second direction of this area partition, to obtain the projected mutual capacitance of this area partition.