Touch sensor device and electronic apparatus having the same

1. A touch sensor device, comprising:

a first human body contact part which forms a capacitance between a human body and the first human body contact part itself when the human body makes a contact or approaches thereto:

a power supply part which outputs an AC voltage to the first human body contact part;

a current detecting part which detects a current flown from the power supply part to the human body;

a reference potential part to be a reference potential of the AC voltage; and

a second human body contact part which is electrically connected to the reference potential part and to which the human body makes a contact,

wherein:

the first human body contact part includes an impedance face formed with a conductive film to which the human body makes a contact or approaches, and a plurality of electrodes which are provided on the impedance face and to which the AC voltage is applied; and

the current detecting part includes a plurality of current detecting circuits which respectively detects currents flown in the plurality of electrodes, and

wherein provided that capacitive impedance formed between the conductive film and the human body when the human body makes a contact or approaches to the conductive film is Z, and parasitic impedance connected in series to the capacitive impedance is Zp, “Zp/Z≦0.4” applies.

2. The touch sensor device as claimed in claim 1 , wherein

the power supply part includes a battery which outputs a DC voltage, transforms the DC voltage to the AC voltage, and outputs the AC voltage from the first human body contact part.

3. The touch sensor device as claimed in claim 2 , which is mounted into a portable device, wherein

the second human body contact part is a conductor which forms a surface of a casing of the portable device.

4. The touch sensor device as claimed in claim 3 , wherein

the conductor forms an entire surface of the casing except periphery of the first human body contact part.

5. The touch sensor device as claimed in claim 3 , wherein

the conductor is a conductive film provided on the surface of the casing.

6. The touch sensor device as claimed in claim 3 , wherein:

the portable device includes a liquid crystal display, a backlight which generates light that transmits through the liquid crystal display, and a conductive folder which reflects the light generated from the backlight and guides the light to the liquid crystal display;

the first human body contact part is provided on a display face of the liquid crystal display; and

the folder and the reference potential part are electrically connected.

7. The touch sensor device as claimed in claim 2 , which is mounted into a portable device, wherein

the second human body contact part includes a conducting wire connected to the reference potential part, and a conductor connected to the conducting wire.

8. The touch sensor device as claimed in claim 2 , which is mounted into a portable device and further includes an indicator, wherein:

the indicator includes a point section which makes a contact with the impedance face, and a grip section grabbed by a hand of the human body; and

the point section and the grip section are both conductive and are electrically connected.

9. The touch sensor device as claimed in claim 8 , wherein

the point section has a same-level elasticity as that of a finger tip of the human body.

10. The touch sensor device as claimed in claim 2 , which is mounted into an onboard device, wherein

the conductor is provided in a part where the human body touches while on board.

11. An onboard device, comprising the touch sensor device claimed in claim 10 .

12. The touch sensor device as claimed in claim 2 , which is mounted into a liquid crystal display that is in a structure in which a liquid crystal is sandwiched between a counter electrode, a pixel electrode, and wirings, wherein:

the counter electrode is used also as the impedance face; and

the touch sensor device further includes a switch part which simultaneously applies the AC voltage applied to the impedance face at least to a part of the wirings.

13. The touch sensor device as claimed in claim 2 , which is mounted into a liquid crystal display that is in a structure in which a liquid crystal is sandwiched between a counter electrode, a pixel electrode, and wirings, wherein:

the counter electrode is used also as the impedance face; and

the touch sensor device further includes a switch part which has at least a part of the wirings electrically floated.

14. The touch sensor device as claimed in claim 2 , which is mounted into a liquid crystal display including a counter electrode, a liquid crystal, and a pixel electrode, the touch sensor device further comprising a switch part which simultaneously applies the AC voltage that is applied to the impedance face to the counter electrode.

15. The touch sensor device as claimed in claim 2 , comprising

a linearization pattern for setting potential distribution of the impedance face provided on a surface of the impedance face.

16. A portable device, comprising the touch sensor device claimed in claim 2 .

17. The touch sensor device as claimed in claim 1 , which is mounted into a liquid crystal display including a counter electrode, a liquid crystal, and a pixel electrode, wherein

the counter electrode is used also as the impedance face;

the pixel electrode is formed on a TFT substrate; and

a linearization pattern for setting potential distribution of the impedance face is provided on the TFT substrate, and is electrically connected to the impedance face via an anisotropic conductor.

18. An electronic device, comprising the touch sensor device claimed in claim 1 .