Proximity detector and proximity detecting method

• US 8,106,668 B2
• Filed: 04/24/2008
• Issued: 01/31/2012
• Est. Priority Date: 10/15/2007
• Status: Expired due to Fees

• Current Assignee: RPX Corporation
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Matsushima, Kenichi
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): Baldridge, Benjamin M
• Application Number:
  US12/150,064
• Publication Number:
  US 20080265914A1
• Time in Patent Office: 1,377 Days
• Field of Search: 324/686
• US Class Current: 324/686
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2017/9602 characterised by the type or shape of the sensing electrodes
• CPC Class Codes: H03K 2017/9613 using two electrodes per touch switch
• CPC Class Codes: H03K 2217/94026 Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03K 2217/960725 Charge-transfer
• CPC Class Codes: H03K 2217/960755 Constructional details of capacitive touch and proximity switches

Abstract

A proximity detector detects the approach of an object based on a stray capacitance. A differential electrode has an apparent stray capacitance that varies in response to an approaching object. An individual capacitance detector detects an individual stray capacitance of the differential electrode based on a stray capacitance of the differential electrode obtained by repeatedly charging and discharging the differential electrode in opposite phases and based on a stray capacitance of the differential electrode obtained by repeatedly charging and discharging the differential electrode in the same phase. A proximity calculator detects the approach of the object based on the detected individual stray capacitance.

Claims

1. A proximity detector for detecting approach of an object based on a stray capacitance, the proximity detector comprising:

at least one differential electrode having an apparent stray capacitance that varies in response to an approaching object, the at least one differential electrode comprising a pair of electrodes having a positive element electrode and a negative element electrode;

an individual capacitance detector for detecting an individual stray capacitance of the differential electrode based on stray capacitances of the pair of electrodes obtained by repeatedly charging and discharging the pair of electrodes at the same time in opposite phases, and by repeatedly charging and discharging the pair of electrodes at the same time in the same phase; and

a proximity calculator for detecting the approach of the object based on the detected individual stray capacitance;

wherein the individual capacitance detector comprises a capacitance sum detector that detects a sum of the obtained stray capacitances of the pair of electrodes, a capacitance difference detector that detects a difference between the obtained stray capacitances of the pair of electrodes, and an individual capacitance calculator that calculates a capacitance of each of the positive and negative electrodes based on the sum detected by the capacitance sum detector and the difference detected by the capacitance difference detector; and

wherein the capacitance difference detector comprises a common-mode charger/discharger that charges and discharges the pair of electrodes in the same phase, and a capacitance difference accumulation unit that accumulates a characteristic of the charge/discharge in the common-mode charger/discharger for a plurality of times and that detects the electrostatic capacitances of the positive and negative electrodes to obtain the differences between the electrostatic capacitances.

2. A proximity detector for detecting at least one of approach and position of an object based on a stray capacitance, the proximity detector comprising:

a plurality of differential electrodes arranged on a support and comprised of a plurality of pairs of electrodes each having a positive electrode and a negative electrode;

an individual capacitance detector for detecting an individual stray capacitance of each of the plurality of differential electrodes from stray capacitances of each pair of electrodes obtained by, for each pair of electrodes, repeatedly charging and discharging the positive and negative electrodes at the same time in opposite phases, and by repeatedly charging and discharging the pair of electrodes at the same time in the same phase; and

a proximity calculator for computing at least one of the approach and the position of the object based on the detected individual stray capacitance of each of the plurality of differential electrodes;

wherein the individual capacitance detector comprises a capacitance sum detector that, for each pair of electrodes of each differential electrode, detects a sum of the obtained stray capacitances of the pair of electrodes, a capacitance difference detector that, for each pair of electrodes of each differential electrode, detects a difference between the obtained stray capacitances of the pair of electrodes, and an individual capacitance calculator that, for each pair of electrodes of each differential electrode, calculates a capacitance of each of the positive and negative electrodes based on the sum detected by the capacitance sum detector and the difference detected by the capacitance difference detector; and

wherein the capacitance difference detector comprises a common-mode charger/discharger that, for each pair of electrodes of each differential electrode, charges and discharges the positive and negative electrodes in the same phase, and a capacitance difference accumulation unit that accumulates a characteristic of the charge/discharge in the common-mode charger/discharger for a plurality of times and that detects the electrostatic capacitances of the positive and negative electrodes of each of the differential electrodes to obtain the differences between the electrostatic capacitances.