Coordinate input device and display-integrated type coordinate input device capable of directly detecting electrostatic coupling capacitance with high accuracy

• US 6,239,788 B1
• Filed: 08/07/1998
• Issued: 05/29/2001
• Est. Priority Date: 08/08/1997
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Takahama, Kengo, Iwahashi, Hiroyuki, Nozaki, Kiyohiro, Katagiri, Masayuki, Nohno, Hitoshi
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Piziali, Jeff
• Application Number:
  US09/131,394
• Time in Patent Office: 1,026 Days
• Field of Search: 345/156, 345/157, 345/173, 345/174, 345/177, 345/179, 345/182, 345/183, 178/18.01-18.03, 178/18.06, 178/18.07, 178/19.03, 178/19.06, 382/315
• US Class Current: 345/173
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• 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: G09G 3/3611 Control of matrices with row and column drivers

Abstract

In a coordinate detection period, a first electrode drive circuit sequentially selects source electrodes Sn of the TFT LCD panel to connect the same to an x-signal current amplifying circuit, and to apply an AC voltage to the non-selected electrodes. The x-signal current amplifying circuit detects a detection current flowing through the selected electrode, the magnitude of which corresponds to a distance to a finger (or a conductor pen), to obtain an x-coordinate detection voltage. A second electrode drive circuit and a y-signal current amplifying circuit operate in similar fashion to obtain a y-coordinate detection voltage. A coordinate detection circuit then obtains the x- and y-coordinate values of the designated position based on the x-coordinate detection voltage and the y-coordinate detection voltage, thus enabling pointing by a codeless pen and a finger.

Claims

1. A coordinate input device, comprising:

a tablet including first electrodes that are parallel to one another at specified intervals, and second electrodes also parallel to one another at specified intervals, but in a direction crossing the direction of the first electrodes, wherein the first electrodes are insulated from the second electrodes;

a DC voltage generating means for generating a DC power voltage;

a control means for outputting a detection control signal used to detect designated coordinates on the tables;

an AC applying means for generating a superimposition voltage and a superimposition detection control signal, by superimposing an AC voltage of identical phase and amplitude on both the DC power voltage and the detection control signal;

an electrode drive means for selecting ones among the first and second electrodes based on the superimposition detection control signal, and for applying the superimposition voltage to non-selected electrodes; and

a coordinate detecting means for detecting a current flowing through the selected electrode and detecting the designated coordinates on the tablet based on this current.

2. A coordinate input device as claimed in claim 1,

wherein the coordinate detecting means includes an AC component removing means for removing the superimposed AC voltage.

3. A coordinate input device as claimed in claim 1,

wherein the superimposed AC voltage has a frequency at which an impedance of the DC voltage generating means is minimized, or is at a frequency near to the frequency of minimum impedance.

4. A coordinate input device as claimed in claim 1,

wherein the coordinate detecting means includes a sample hold circuit, and

wherein the detection control signal includes a clock signal that is synchronized with the superimposed AC voltage, and which is supplied to the sample hold circuit so as to instruct a sample hold timing.

5. A coordinate input device as claimed in claim 1,

wherein at least two superimposition voltages having the same phase and amplitude are generated by superimposing the AC voltage on the DC power voltage by the AC applying means, and

wherein supply lines of the superimposition voltages are connected to each other via a capacitor having a capacitance not smaller than a specified capacitance.

6. A coordinate input device as claimed in claim 1, wherein

the DC voltage generating means includes a DC-to-DC converter.

7. A coordinate input device as claimed in claim 1, wherein

a loop-shaped electric path is formed at least around an outer periphery of the tablet.

8. A coordinate input device as claimed in claim 1, wherein

a plurality of electrodes are simultaneously selected by the electrode drive means.

9. A coordinate input device as claimed in claim 8,

wherein the product of the number and arrangement pitch of the electrodes that are simultaneously selected by the electrode device means is set to be within a range of about 10 mm to 30 mm.

10. A coordinate input device as claimed in claim 1,

wherein the control means outputs a detection control signal for making a selection period for the first electrodes overlap a selection period for the second electrodes;

and

wherein the coordinate detecting means further includes an x-coordinate detecting means for detecting an x-coordinate value on the tablet, based on a current flowing through the first electrode selected by the electrode drive means, and a y-coordinate detecting means for detecting a y-coordinate value based on a current flowing through the selected second electrode.

11. A coordinate input device as claimed in claim 10,

wherein the detection control signal is a detection control signal that initiates selection of either one of the first electrode and the second electrode, and then initiates selection of the other.

12. A coordinate input device as claimed in claim 1,

further comprising an electrode provided at a position in which it can be electrostatically coupled with a human body, wherein said electrode is connected to a DC reference potential point.

13. A display-integrated type coordinate input device, comprising:

an image display panel including first electrodes that are parallel to one another at specified intervals, and second electrodes also parallel to one another at specified intervals, but in a direction crossing the direction of the first electrodes, wherein the first electrodes are insulated from the second electrodes;

a DC voltage generating means for generating a DC power voltage;

a control means for outputting a display control signal for displaying an image on the image display panel during a display period of one frame, and for outputting a detection control signal used to detect designated coordinates on the image display panel during a coordinate detection period of the one frame;

an AC applying means for generating a superimposition voltage and a superimposition detection control signal, by superimposing an AC voltage of identical phase and amplitude on both the DC power voltage and the detection control signal;

an electrode drive means for displaying an image on the image display panel by driving the first electrodes and the second electrodes on the basis of the display control signal during the display period, selecting the first electrode and the second electrode based on the superimposition detection control signal, and applying the superimposition voltage to non-selected electrodes during the coordinate detection period; and

a coordinate detecting means for detecting a current flowing through the selected electrodes and for detecting the designated coordinates on the image display panel based on this current.

14. A display-integrated type coordinate input device as claimed in claim 13,

wherein the first and second electrodes are formed on an identical substrate, and

wherein a plurality of switching elements connected to the first and second electrodes, and transparent pixel electrodes connected to the switching elements, are arranged in a matrix form,

the coordinate input device further comprising:

an opposite substrate on which an opposite electrode opposite to the transparent pixel electrode is formed, wherein the opposite substrate is arranged opposite to the identical substrate; and

liquid crystals filled in a space between the pixel electrode and the opposite electrode.

15. A display-integrated type coordinate input device as claimed in claim 14,

wherein the superimposition voltage applied to those non-selected electrodes of said first and second electrodes is a voltage that makes the switching elements non-conductive.

16. A display-integrated type coordinate input device as claimed in claim 13,

wherein the control means outputs a detection control signal for making a selection period for the first electrodes overlap a selection period for the second electrodes;

and

wherein the coordinate detecting means further includes an x-coordinate detecting means for detecting an x-coordinate value on the image display panel based on a current flowing through the first electrode selected by the electrode drive means, and a y-coordinate detecting means for detecting a y-coordinate value based on a current flowing through the selected second electrode.

17. A display-integrated type coordinate input device as claimed in claim 13,

wherein the image display panel is a duty ratio type image display panel in which the first electrode and the second electrode are formed of transparent electrodes on different transparent substrates,

wherein liquid crystals are filled in a space between the different transparent electrodes;

and

wherein the coordinate detecting means further includes an x-coordinate detecting means for detecting an x-coordinate value on the image display panel based on a current flowing through the selected first electrode, and a y-coordinate detecting means for detecting a y-coordinate value based on a current flowing through the selected second electrode.

18. A display-integrated type coordinate input device as claimed in claim 17,

wherein at least one of the x-coordinate and y-coordinate detecting means is provided with an envelope detecting means and a waveform differentiating means, and

wherein the designated coordinates are detected based on an envelope differential waveform of the detection current.

19. A display-integrated type coordinate input device as claimed in claim 17,

wherein the control means outputs a detection control signal for making a selection period for the first electrodes overlap a selection period for the second electrodes.

20. A display-integrated type coordinate input device as claimed in claims 16,

wherein the detection control signal initiates selection of either one of the first electrode and the second electrode, and then initiates selection of the other.

21. A display-integrated type coordinate input device as claimed in claims 17,

wherein the detection control signal initiates selection of either one of the first electrode and the second electrode, and then initiates selection of the other.