Active matrix touch sensing

• US 8,619,055 B2
• Filed: 04/14/2008
• Issued: 12/31/2013
• Est. Priority Date: 04/14/2008
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Westerinen, William J., Ranta, Craig Steven
• Primary Examiner(s): Zhou, Hong
• Application Number:
  US12/102,024
• Publication Number:
  US 20090256815A1
• Time in Patent Office: 2,087 Days
• Field of Search: 345173-174, 178 1801- 2001
• US Class Current: 345/174
• 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

An active matrix for a capacitive multiple touch sensing device is disclosed. One embodiment comprises one or more active matrix capacitive touch sensing pixels that each include a capacitor and a thin film transistor, wherein a voltage can be applied to the thin film transistor to address the capacitor. In this way, the thin film transistor can operate as a switch to apply an alternating current to the capacitor, and the capacitor'"'"'s capacitance can be measured in relation to the alternating current and an externally applied electric field.

Claims

1. An active matrix capacitive touch sensing device with an array of pixels, the device comprising:

a glass substrate including a first side to accept touch input and a second side;

a plurality of rows of pixels, each row being coupled with a metal drive bus;

a plurality of columns of pixels, each column being coupled with a metal sense bus;

a voltage source switchably coupled with a metal pixel select bus for each row of pixels, the voltage source configured to select a row of pixels by providing a voltage to that row of pixels; and

a first analog multiplexer to sequentially couple the metal sense bus for each column in the array with sense circuitry;

each pixel of the array of pixels comprising;

a capacitor including a first layer on the first side of the glass substrate and a second layer on the second side of the glass substrate;

a thin film transistor having a drain, a source, and a gate, the drain being coupled directly with the first layer of the capacitor;

a metal pixel select bus coupled directly with the gate of the thin film transistor, the metal pixel select bus to supply a voltage to the gate of the thin film transistor to actively address the capacitor, wherein the metal pixel select bus is held at a negative voltage in a nonselected state and a positive voltage in a selected state;

a metal drive bus coupled with the second terminal of the thin film transistor, the metal drive bus to supply an alternating current signal to the second, wherein the metal pixel select bus, the thin film transistor, and the metal drive bus are on the first side of the glass substrate;

a metal sense bus coupled with the second layer of the capacitor on the second side of the glass substrate, the metal sense bus to transmit a current that varies with the capacitance of the capacitor to the sense circuitry in response to the alternating current signal received at the source of the thin film transistor and further in response to an electric field applied from an external input to the active matrix capacitive touch sensing device; and

wherein the sense circuitry is configured to detect a first change in capacitance of at least one capacitor of the array of pixels to indicate an external passive touch input at or near the at least one capacitor, detect a second change in capacitance of at least one capacitor of the array of pixels that is different from the first change in capacitance, wherein the second change in capacitance indicates an active device applying an external current signal at or near the at least one capacitor, and distinguish input of the active device from input of the external passive touch input based on the difference between the first change in capacitance and the second change in capacitance.

2. The active matrix capacitive touch sensing device of claim 1, further comprising a second analog multiplexer to sequentially inject the alternating current signal to each of the plurality of rows of pixels, wherein the voltage source is further configured to switch on each of the plurality of row of pixels while the alternating current signal is injected.

3. The active matrix capacitive touch sensing device of claim 1, wherein the first layer and the second layer of each capacitor are indium tin oxide.

4. The active matrix capacitive touch sensing device of claim 1, wherein each metal pixel select bus and each metal drive bus are aluminum.

5. The active matrix capacitive touch sensing device of claim 1, coupled with circuitry to integrate the capacitance over multiple alternating current cycles.

6. The active matrix capacitive touch sensing device of claim 1, wherein the voltage source provides a negative voltage to each non-selected metal pixel select bus in order to reduce leakage current.

7. The active matrix capacitive touch sensing device of claim 1, wherein the first layer of the capacitor is either hard coated or covered with a thin protective layer.

8. The active matrix capacitive touch sensing device of claim 1, wherein the sense circuitry includes at least one sense amplifier.

9. A method for using an active matrix in a capacitive multiple touch sensing device, the active matrix comprising a plurality of pixels arranged in rows and columns, each pixel including a capacitor coupled with a thin film transistor having a drain, a source, and a gate, the drain being coupled directly with a first layer of the pixel, each row of pixels coupled directly with a metal drive bus through the source, and each column of pixels coupled directly with a metal sense bus that is coupled to sense circuitry, each row of pixels further coupled directly with a metal pixel select bus through the gate, the method comprising:

applying a positive voltage to a metal pixel select bus of a selected row of pixels from a voltage source on a first side to accept touch input of glass substrate to form a channel in each transistor in the selected row of pixels coupled with the metal pixel select bus;

applying a negative voltage to other metal pixel select buses of nonselected rows of pixels to maintain thin film transistors of pixels in the nonselected rows in an off state;

applying an alternating current signal from an alternating current source that is different than the voltage source to a plurality of capacitors through a metal drive bus on the first side of the glass substrate and through a transistor coupled to that capacitor;

sensing a capacitance of each of the plurality of capacitors via the metal sense bus on a second side of the glass substrate using the sense circuitry;

detecting a first change in a capacitance of at least one capacitor of the plurality of capacitors to indicate an external passive touch input at or near that at least one capacitor;

detecting a second change in capacitance of at least one capacitor of the plurality of capacitors that is different from the first change in capacitance, wherein the second change in capacitance indicates an active device applying an external current signal at or near the at least one capacitor; and

distinguishing input of the active device from input of the external passive touch input based on the difference between the first change in capacitance and the second change in capacitance.

10. The method of claim 9, further comprising:

sequentially applying a voltage to each metal pixel select bus and an alternating current to each metal drive bus;

sequentially sensing, for each pixel in the capacitive multiple touch sensing device, a change in a capacitance of each pixel'"'"'s capacitor using the sense circuitry.

11. The method of claim 9, further comprising integrating a plurality of capacitances for a single capacitor over multiple alternating current cycles.