Real contact type touch panel apparatus

• US 6,373,474 B1
• Filed: 10/26/1999
• Issued: 04/16/2002
• Est. Priority Date: 10/27/1998
• Status: Expired due to Term

• Current Assignee: Pentel Kabushiki Kaisha
• Original Assignee: Pentel Kabushiki Kaisha
• Inventors: Katabami, Koichiro
• Primary Examiner(s): Liang, Regina
• Application Number:
  US09/426,531
• Time in Patent Office: 903 Days
• Field of Search: 345/173, 345/174, 345/175, 345/177, 345/178, 345/179, 178/18.01, 178/18.03, 178/18.05, 178/18.06, 178/18.07, 178/19.01, 178/19.03, 178/19.06, 178/19.07, 178/20.01
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners

Abstract

A touch panel apparatus has a sensor panel using a tin oxide resistive film that avoids the palm effect and has an improved noise margin and S/N ratio. A finger or conductor is brought into direct contact with the touch panel and injected with an AC signal of 200 kHz or more, a signal current is detected, and the current is converted into a voltage by a transistor connected to an LC resonance circuit. The touch panel is contained in a voltage-floating system insulated from a non-floating system through a capacitor of 5000 pF or less and has an A/D converter in which a step-shaped triangular wave is superimposed on a measured voltage so that output at each step of an analog/digital converter is added.

Claims

1. A real contact type touch panel apparatus in which a conductive surface disposed on a sensor panel is directly contacted by a finger or a conductor, the real contact type touch panel apparatus comprising:

a voltage-floating system comprising the sensor panel having the conductive surface disposed thereon, a signal processing unit connected to the sensor panel, and a reference potential circuit connected to the signal processing unit;

a non-floating system comprising an interface connected to an external apparatus, and a ground circuit; and

an isolator for transmitting digital or analog electric information between the signal processing unit and the interface;

wherein the reference potential circuit of the voltage-floating system is connected in series to the ground circuit of the non-floating system through an AC signal generator and an AC signal coupling capacitor, the AC signal coupling capacitor having a capacity of 5000 pF or less, the signal processing unit has an input circuit operating as a current/voltage conversion circuit comprising a transistor and a resonance circuit connected to an output of the transistor, the transistor having a base or gate grounded in an AC condition with respect to the current/voltage conversion circuit, an emitter or source into which an AC signal is input, and a collector or drain connected to the resonance circuit, and the resonance circuit comprises a coil and a capacitor.

2. The real contact type touch panel apparatus according to claim 1;

wherein the conductive surface comprises a uniform surface resistor, the conductor is a conductive pen, and a detected location on the sensor panel is touched by the conductive pen or the finger.

3. The real contact type touch panel apparatus according to claim 2;

wherein the surface resistor comprises tin oxide.

4. The real contact type touch panel apparatus according to claim 2;

further comprising A/D conversion means used as signal level measuring means for calculating the contact location, the A/D conversion means comprising means for superposing a step-shaped triangular wave on an output voltage level of an AC/DC converter, the step-shaped triangular wave being generated with an amplitude of 2 or more times the LSB of an analog/digital converter, and means for adding an output at each step of the analog/digital converter.

5. A real contact type touch panel apparatus used with a system to be fed from at least one of a battery, an insulating transformer, or a dedicated generator, in which a conductive surface disposed on a sensor panel is directly contacted by a finger or a conductor, the direct contact type touch panel apparatus comprising:

a voltage-floating system comprising the sensor panel having the conductive surface disposed thereon, a signal processing unit connected to the conductive surface, a reference potential circuit connected to the signal processing unit;

a non-floating system comprising an interface connected to an external apparatus, and a ground circuit, signal lines for connecting the signal processing unit to the interface for receiving and transmitting therein and therefrom digital or analog electric information; and

an AC signal generator provided between the reference potential circuit of the voltage-floating system and the ground circuit of the non-floating system;

wherein the signal processing unit has an input circuit operating as a current/voltage conversion circuit comprising a transistor and a resonance circuit, the transistor having a base or gate grounded in an AC condition with respect to the current/voltage conversion circuit, an emitter or source into which an AC signal is input, and a collector or drain connected to the resonance circuit, and the resonance circuit comprises a coil and a capacitor.

6. The real contact type touch panel apparatus according to claim 5;

wherein the conductive surface comprises a uniform surface resistor, the conductor is a conductive pen, and a detected location on the sensor panel is touched by the conductive pen or the finger.

7. The real contact type touch panel apparatus according to claim 6;

wherein the surface resistor comprises tin oxide.

8. The real contact type touch panel apparatus according to claim 6;

further comprising A/D conversion means used as signal level measuring means for calculating the contact location, the A/D conversion means comprising means for superposing a step-shaped triangular wave on an output voltage level of an AC/DC converter, the step-shaped triangular wave being generated with an amplitude of 2 or more times the LSB of an analog/digital converter, and means for adding an output at each step of the analog/digital converter.

9. In a real contact type touch panel apparatus in which a conductive surface on a sensor panel is brought into electrical direct contact with a finger or a conductor connected to the apparatus;

means for introducing an AC signal current at frequency of 200 or more kHz to the finger or the conductor through the conductive surface; and

means for measuring the AC signal current including one or more current components which are produced by the grounding effect of electromagnetic radiant impedance of an operator'"'"'s body with the finger or the conductor.

10. A direct contact type touch panel apparatus comprising:

a sensor panel having a conductive surface;

a signal processing unit connected to the sensor panel;

a reference potential generating circuit connected to the signal processing unit;

an interface connected to an external apparatus for communicating with the external apparatus;

a ground circuit; and

an isolator for transmitting digital or analog electric information between the signal processing unit and the interface;

wherein the sensor panel, the signal processing unit, and the reference potential generating circuit comprise a voltage-floating system and the interface and the ground circuit comprise a non-floating system isolated from the floating system.

11. A direct contact type touch panel apparatus according to claim 10;

wherein the reference potential generating circuit is connected in series to the ground circuit through an AC signal generator and an AC signal coupling capacitor, the AC signal coupling capacitor having a capacity of 5000 pF or less.

12. A direct contact type touch panel apparatus according to claim 10;

wherein the signal processing unit has an input circuit operating as a current/voltage conversion circuit comprising a transistor and a resonance circuit comprising a coil and a capacitor connected in parallel, the transistor having a base or gate grounded in an AC condition, an emitter or source into which an AC signal is input, and a collector or drain connected to the resonance circuit.

13. A direct contact type touch panel apparatus according to claim 10;

wherein the signal processing unit is connected to the reference potential generating circuit.

14. A direct contact type touch panel apparatus according to claim 10;

wherein the conductive surface comprises a surface resistor, the conductor is a conductive pen, and a detected location on the sensor panel is touched by the conductive pen or an operator'"'"'s finger.

15. A direct contact type touch panel apparatus according to claim 10;

wherein the surface resistor comprises tin oxide.

16. A direct contact type touch panel apparatus according to claim 10;

further comprising means for flowing an AC signal current having a frequency of 200 kHz or more into the finger or conductor through the conductive surface.

17. A direct contact type touch panel apparatus according to claim 10;

further comprising A/D conversion means used as signal level measuring means for calculating the contact location of the finger or conductor, the A/D conversion means comprising an AC/DC converter, an analog/digital converter, and means for superposing a step-shaped triangular wave on an output voltage of the AC/DC converter, the step-shaped triangular wave being generated with amplitude of 2 or more times the LSB of the analog/digital converter.