Coordinate input device

• US 5,905,489 A
• Filed: 02/12/1997
• Issued: 05/18/1999
• Est. Priority Date: 02/16/1996
• Status: Expired due to Term

• 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, Nohno, Hitoshi
• Primary Examiner(s): Wu, Daniel J.
• Application Number:
  US08/799,425
• Time in Patent Office: 825 Days
• Field of Search: 345/156, 345/173, 345/180, 345/182, 345/174
• US Class Current: 345/174
• 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

Abstract

An M-sequence signal is generated in an M-sequence generation circuit, and the M-sequence signal, which is successively delayed by a column-electrode driving circuit or a row-electrode driving circuit, is applied to a column-electrode group or a row-electrode group. A correlator finds a correlation between the M-sequence signal and a detection signal that has been detected by amplifying electrostatically induced voltage that appeared in the detection electrode of an electronic pen so that a position specified by the electronic pen is detected by a detection circuit as a coordinate signal. Thus, it is possible to obtain a coordinate detection signal having a superior S/N ratio without reducing the coordinate detection speed, and consequently to carry out a coordinate detecting operation with high precision.

Claims

1. A coordinate input device, which detects coordinates on a surface that are specified by an indicator, and outputs the resulting coordinate data, comprising:

a first group of electrodes arranged on a substrate at predetermined intervals;

a second group of electrodes, insulated from the first group of electrodes, and arranged at predetermined intervals so as to intersect the first group of electrodes;

a pseudo-random-signal generator for generating a pseudo-random signal having a pulse-related auto-correlation function;

a first sequential driver for sequentially applying the pseudo-random signal having alternately different phases to respective electrodes of the first group of electrodes;

a second sequential driver for sequentially applying the pseudo-random signal having alternately different phases to respective electrodes of the second group of electrodes;

a correlation detector for detecting correlation between a detection signal, outputted from the indicator when the indicator is electrostatically coupled to the first or second group of electrodes, and the pseudo-random signal generated by the pseudo-random-signal generator; and

a coordinate output device, adapted to determine a time difference forming an extreme value of the detection signal detected by the correlation detector, and output a coordinate value corresponding to the time difference as a specified coordinate.

2. The coordinate input device as defined in claim 1, wherein the pseudo-random signal is a binary-sequence signal formed only of binary levels, and the correlation detector includes a delay device which successively delays the detection signal that has been inputted to the correlation detector and converted into a digital signal, and outputs a resulting signal, a first adder which adds the outputs a resulting signal, a first adder which adds the outputs of the delay device corresponding to a high-level coefficient of the binary sequence signal, a second adder which adds the outputs of the delay device corresponding to a low-level coefficient of the binary sequence signal, and a subtracter which calculates a difference between outputs of the first and second adders.

3. The coordinate input device as defined in claim 1, further comprising a low-pass filter, located between the correlation detector and the coordinate output device, which suppresses the high-frequency component of the output from the correlation detector.

4. The coordinate input device as defined in claim 3, wherein the low-pass filter is a matched filter, weighted based on a coupling capacitance resulting from the indicator.

5. The coordinate input device as defined in claim 4, wherein the coordinate output device includes a correction device for applying a quadratic-curve interpolation to an output from the matched filter.

6. The coordinate input device as defined in claim 4, wherein the low-pass filter is an infinite impulse response filter.

7. The coordinate input device as defined in claim 1, included within a display-integrated-type coordinate input device further comprising:

an information-processing device for driving an application program so as to generate display data upon receipt of the specified coordinates outputted from the coordinate output device;

a display control device for generating a control signal for driving the first or second sequential driver based on the display data outputted from the information-processing device;

an output-switching device for selectively outputting the control signal from the display control device and the pseudo-random signal from the pseudo-random-signal generator in a time sharing manner; and

a display device for providing a liquid crystal display using the first and second groups of electrodes,

wherein an image is displayed by controlling light transmittance of a liquid crystal using an electric signal released from the first or second sequential driver during a display period in which the control signal has been selected by the output-switching device.

8. The coordinate input device as defined in claim 7, wherein said display device comprises:

a plurality of electrode-group switching elements connected to the first and second electrode groups, and transparent pixel electrodes, wherein a plurality of pixel electrodes, connected to the electrode-group switching elements, are arranged in a matrix format, and opposing electrodes face the transparent pixel electrodes with liquid crystal interpolated in between, said coordinate input device being arranged so that during the coordinate detection period in which the pseudo-random signal has been selected by the output-switching device, a voltage, which does not allow the electrode-group switching elements to conduct, is applied to the first electrode group or the second electrode group.

9. The coordinate input device as defined in claim 7, wherein said display device comprises a first transparent substrate on which the first electrode group is placed and a second transparent substrate on which the second electrode group is placed, the second transparent substrate facing the first transparent substrate, with the liquid crystal interpolated therebetween, said coordinate input device being arranged so that optical properties of the liquid crystal are controlled by an effective applied voltage of the first electrode group and the second electrode group.

10. The coordinate input device as defined in claim 1, wherein the pseudo-random signal is an M-sequence signal.

11. The coordinate input device as defined in claim 1, wherein the pseudo-random signal is an analog signal.

12. The coordinate input device as defined in claim 1, wherein the correlation detector comprises an analog delay device which successively delays the detection signal inputted to the correlation detector as an analog signal, and which outputs a resulting signal, a plurality of impedance elements to which the outputs from the analog delay device are inputted and having values corresponding to the coefficients of the pseudo-random signals, and an amplifier whose integrated values are determined by the values of the impedance elements.

13. The coordinate input device as defined in claim 12, wherein said impedance elements are capacitors and said amplifier is a complementary MOS circuit.

14. A coordinate input device, which detects coordinates on a surface that are specified by a conductive indicator, and outputs the resulting coordinate data, comprising:

a first group of electrodes arranged on a substrate at predetermined intervals;

a second group of electrodes insulated from the first group of electrodes and arranged at predetermined intervals so as to intersect the first group of electrodes;

a pseudo-random-signal generator for generating a pseudo-random signal having a pulse-related auto-correlation function;

a first sequential driver for sequentially applying the pseudo-random signal having alternately different phases to respective electrodes of the first group of electrodes;

a second sequential driver for sequentially applying the pseudo-random signal having alternately different phases to respective electrodes of the second group of electrodes;

a correlation detector which detects correlation between the pseudo-random signal, generated by the pseudo-random-signal generator, and a detection signal that has been induced in an electrode group not being driven, due to the fact that the indicator, electrostatically coupled to the electrode group being driven by the first or second sequential driver, is also electrostatically coupled to the electrode group not being driven; and

a coordinate output device, adapted to determine a time difference forming an extreme value of the detection signal detected by the correlation detector, and output a coordinate value corresponding to the time difference as a specified coordinate.

15. The coordinate input device as defined in claim 14, wherein the pseudo-random signal is a binary-sequence signal formed only of binary levels, and the correlation detector includes a delay device which successively delays the detection signal that has been inputted to the correlation detector and converted into a digital signal, and outputs a resulting signal, a first adder which adds the outputs of the delay device corresponding to a high-level coefficient of the binary sequence signal, a second adder which adds the outputs of the delay device corresponding to a low-level coefficient of the binary sequence signal, and a subtracter which calculates a difference between outputs of the first and second adders.

16. The coordinate input device as defined in claim 14, further comprising a low-pass filter, located between the correlation detector and the coordinate output device, which suppresses the high-frequency component of the output from the correlation detector.

17. The coordinate input device as defined in claim 16, wherein the low-pass filter is a matched filter, weighted based on a coupling capacitance resulting from the indicator.

18. The coordinate input device as defined in claim 17, wherein the coordinate output device including a correction device for applying a quadratic-curve interpolation to an output from the matched filter.

19. The coordinate input device as defined in claim 16, wherein the low-pass filter is an infinite impulse response filter.

20. The coordinate input device as defined in claim 14, included within a display-integrated-type coordinate input device further comprising:

an information-processing device for driving an application program so as to generate display data upon receipt of the specified coordinates outputted from the coordinate output device;

a display control device for generating a control signal for driving the first or second sequential driver based on the display data outputted from the information-processing device;

an output-switching device for selectively outputting the control signal from the display control device and the pseudo-random signal from the pseudo-random-signal generator in a time sharing manner; and

a display device for providing a liquid crystal display using the first and second groups of electrodes,

wherein an image is displayed by controlling light transmittance of a liquid crystal using an electric signal released from the first or second sequential driver during a display period in which the control signal has been selected by the output-switching device.

21. The coordinate input device as defined in claim 20, wherein said display device comprises:

a plurality of electrode-group switching elements connected to the first and second electrode groups, and transparent pixel electrodes wherein a plurality of pixel electrodes, connected to the electrode-group switching elements, are arranged in a matrix format, and opposing electrodes face the transparent pixel electrodes with liquid crystal interpolated in between, said coordinate input device being arranged so that during the coordinate detection period in which the pseudo-random signal has been selected by the output-switching device, a voltage, which does not allow the electrode-group switching elements to conduct, is applied to the first electrode group or the second electrode group.

22. The coordinate input device as defined in claim 20, wherein said display device comprises a first transparent substrate on which the first electrode group is placed and a second transparent substrate on which the second electrode group is placed, the second transparent substrate facing the first transparent substrate, with the liquid crystal interpolated therebetween, said coordinate input device being arranged so that optical properties of the liquid crystal are controlled by an effective applied voltage of the first electrode group and the second electrode group.

23. The coordinate input device as defined in claim 14, wherein the pseudo-random signal is an M-sequence signal.

24. The coordinate input device as defined in claim 14, wherein the pseudo-random signal is an analog signal.

25. The coordinate input device as defined in claim 14, wherein the correlation detector comprises an analog delay device which successively delays the detection signal inputted to the correlation detector as an analog signal, and which outputs a resulting signal, a plurality of impedance elements to which the outputs from the analog delay device are inputted and having values corresponding to the coefficients of the pseudo-random signals, and an amplifier whose integrated values are determined by the values of the impedance elements.

26. The coordinate input device as defined in claim 25, wherein said impedance elements are capacitors and said amplifier is a complementary MOS circuit.

27. The coordinate input device as defined in claim 14, further comprising:

a second indicator for specifying a coordinate position on the first and second groups of electrodes by being coupled to the first or second group of electrodes;

a second correlation detector for detecting correlation between a detection signal outputted from the second indicators and the pseudo-random signal generated by the pseudo-random-signal generator; and

a second coordinate output device, adapted to determine a time difference forming an extreme value of the detection signal detected by the second correlation detector, and output a coordinate value corresponding to the time difference as a specified coordinate.

28. The coordinate input device as defined in claim 14, further comprising:

a second indicator for specifying a coordinate position on the first and second groups of electrodes by being coupled to the first or second group of electrodes; and

a switch for selectively inputting to the correlation detector a detection signal outputted from the second indicator and a detection signal induced in the electrode group not driven.

29. The coordinate input device as defined in claim 28, wherein said switch carries out selection of the two detection signals in a time-sharing manner.