Capacitance detecting apparatus and its inspecting method and fingerprint checking apparatus

• US 6,681,033 B1
• Filed: 11/12/1999
• Issued: 01/20/2004
• Est. Priority Date: 11/16/1998
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Takeda, Masashi, Koyama, Takeshi, Yano, Motoyasu, Shinozaki, Keiichi
• Primary Examiner(s): Werner, Brian
• Assistant Examiner(s): Miller, Ryan J.
• Application Number:
  US09/439,084
• Time in Patent Office: 1,530 Days
• Field of Search: 382/124, 382/125, 382/126, 382/108, 356/71, 340/5.53, 340/5.83, 707/6, 713/186, 713/200, 902/3, 902/6
• US Class Current: 382/124
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01D 5/2405 by varying dielectric
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

When a current charge method is used as a method of detecting capacitance, there poses a problem in which S/N is deteriorated by a dispersion in element characteristics of a cell to be detected and when a voltage charge method is used, since parasitic capacitances of column sense lines are very large and accordingly, there is needed some devise for sampling electric charge charged to the capacitance. There are arranged unit cells having detection electrodes and cell selecting switches connected between the detection electrodes and column sense lines in an array shape, electric charge is charged from detecting circuits to the detection electrodes under constant charge voltage, and thereafter, the column sense lines are imaginarily grounded to thereby detect the capacitances formed between the detection electrodes and the surface of the finger in accordance with recesses and projections of a fingerprint via the column sense lines.

Claims

1. A capacitance detecting apparatus comprising:

unit cells having detection electrodes and switching elements connected between the detection electrodes and sense lines and arranged in an array shape;

charging and discharging circuits for charging electric charge to said detection electrodes under constant voltage and discharging the electric charge; and

detecting circuits for imaginarily grounding said sense lines after charging the electric charge to said detection electrodes and detecting the electric charge of said detection electrodes via the sense lines to thereby detect capacitances formed between a detection object and the detection electrodes,

wherein said sense lines serve also as charge and/or discharge lines of said charging and discharging circuits,

wherein said detecting circuits serve also as said charging and discharging circuits,

wherein said detecting circuit comprises;

an operational amplifier an inverse phase input end of which is connected to said sense line and a positive phase input end of which is applied alternatively with said constant voltage or a predetermined reference voltage;

a feedback capacitor connected between the inverse phase input end and an output end of the operational amplifier; and

a bypass switch for selectively bypassing said feedback capacitor.

2. The capacitance detecting apparatus according to claim 1:

wherein the capacitance formed between the detection object and said detection electrode is capacitance formed between the detection electrode and a surface of a finger in accordance with recesses and projections of a fingerprint.

3. The capacitance detecting apparatus according to claim 1:

wherein said switching element comprises an MOS transistor or a CMOS transistor a source or a drain of which is connected to said detection electrode.

4. The capacitance detecting apparatus according to claim 3:

wherein said MOS transistor or said CMOS transistor serves also as a static electricity protecting element.

5. The capacitance detecting apparatus according to claim 1, further comprising:

holding means for holding a detected output from said detecting circuit.

6. A capacitance detecting apparatus comprising:

unit cells having detection electrodes and switching elements connected between the detection electrodes and sense lines and arranged in an array shape;

detecting means for detecting capacitances formed between a detection object and the detection electrodes by charging electric charge to said detection electrodes and detecting voltage based on the electric charge; and

dummy electrodes having parasitic capacitances substantially equal to parasitic capacitances of said detection electrodes, one of said dummy electrodes being alternately disconnected from and connected to one of said sense lines when one of said detection electrodes is alternately conected to and disconnected from said one of said sense lines;

wherein electric charge of the parasitic capacitances of said detection electrodes is canceled by electric charge of the parasitic capacitances of said dummy electrodes.

7. The capacitance detecting apparatus according to claim 6:

wherein said detecting means comprise;

charging and discharging circuits for charging electric charge to said detection electrodes under constant voltage and discharging the electric charge; and

detecting circuits for imaginarily grounding said sense lines after charging the electric charge to said detection electrodes to thereby detect the electric charge of said detection electrodes via the sense lines.

8. The capacitance detecting apparatus according to claim 7:

wherein said detecting circuit comprises;

an operational amplifier an inverse phase input end of which is connected to said sense line and a positive phase input end of which is applied alternatively with said constant voltage or a predetermined reference voltage Vref;

a feedback capacitor connected between the inverse phase input end and an output end of the operational amplifier; and

a bypass switch for selectively bypassing said feedback capacitor.

9. The capacitance detecting apparatus according to claim 8, further comprising:

an output amplifier for inputting predetermined reference voltage Vos as one input, inputting a detected output Vsns from the detecting circuit as the other input and having a gain A;

wherein when a difference between said reference voltage Vos and a minimum value or a maximum value of an output dynamic range is designated by a notation Vswg, when the reference voltage Vref is applied to said detecting circuit, the reference voltage Vref, the reference voltage Vos and the difference Vswg between the reference voltage Vos and the minimum value of the output dynamic range and the gain A of the output amplifier are set to satisfy the following condition;

10. The capacitance detecting apparatus according to claim 9, further comprising:

a hold circuit for holding a detected output from said detecting circuit between said detecting circuit and said output amplifier;

wherein the gain A of said output amplifier is given by a ratio of a hold capacitor of said hold circuit to the feedback capacitor of said output amplifier.

11. The capacitance detected apparatus according to claim 6:

wherein said dummy electrodes are connected to said sense lines via switching element for respective rows of said unit cells.

12. A capacitance detecting apparatus comprising:

a plurality of detection electrodes, a detection electrode of said plurality of detection electrodes being connected to a row selection line and a sense line;

a plurality of detecting circuits, a detecting circuit of said plurality of detecting circuits detecting an electric charge accumulating within said detection electrode,

said detecting circuit including an operational amplifier, a feedback capacitor and a bypass switch,

said operational amplifier having a positive phase input end, an inverse phase input end, and an output end,

said positive phase input end alternately receiving a constant voltage and a reference voltage,

said inverse phase input end receiving said electric charge from said sense line,

said output end supplying one of said constant voltage and said reference voltage to said sense line,

said feedback capacitor being connected to said inverse phase input end and to said output end,

said bypass switch being connected to said inverse phase input end and to said output end.

13. A fingerprint checking apparatus comprising:

a fingerprint detecting apparatus having a plurality of detection electrodes and a plurality of detecting circuits,

a detection electrode of said plurality of detection electrodes being connected to a row selection line and a sense line,

a detecting circuit of said plurality of detecting circuits detecting an electric charge accumulating within said detection electrode, said detecting circuit including an operational amplifier, a feedback capacitor and a bypass switch,

said operational amplifier having a positive phase input end, an inverse phase input end, and an output end,

said positive phase input end alternately receiving a constant voltage and a reference voltage,

said inverse phase input end receiving said electric charge from said sense line,

said output end supplying one of said constant voltage and said reference voltage to said sense line,

said feedback capacitor being connected to said inverse phase input end and to said output end,

said bypass switch being connected to said inverse phase input end and to said output end.

14. The fingerprint checking apparatus according to claim 13 further comprising:

a storing medium, said storing medium storing fingerprint pattern data which has previously been registered.

15. The fingerprint checking apparatus according to claim 14 further comprising:

a comparing unit, said comparing unit comparing fingerprint data detected by said fingerprint detecting apparatus with said fingerprint pattern data.