Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q3/00—Selecting arrangements
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M11/00—Coding in connection with keyboards or like devices, i.e. coding of the position of operated keys
  • H03M11/22—Static coding
  • H03M11/24—Static coding using analogue means, e.g. by coding the states of multiple switches into a single multi-level analogue signal or by indicating the type of a device using the voltage level at a specific tap of a resistive divider
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M1/00—Substation equipment, e.g. for use by subscribers
  • H04M1/02—Constructional features of telephone sets
  • H04M1/0202—Portable telephone sets, e.g. cordless phones, mobile phones or bar type handsets
  • H04M1/0206—Portable telephones comprising a plurality of mechanically joined movable body parts, e.g. hinged housings
  • H04M1/0208—Portable telephones comprising a plurality of mechanically joined movable body parts, e.g. hinged housings characterized by the relative motions of the body parts
  • H04M1/0214—Foldable telephones, i.e. with body parts pivoting to an open position around an axis parallel to the plane they define in closed position
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M1/00—Substation equipment, e.g. for use by subscribers
  • H04M1/02—Constructional features of telephone sets
  • H04M1/0202—Portable telephone sets, e.g. cordless phones, mobile phones or bar type handsets
  • H04M1/0206—Portable telephones comprising a plurality of mechanically joined movable body parts, e.g. hinged housings
  • H04M1/0241—Portable telephones comprising a plurality of mechanically joined movable body parts, e.g. hinged housings using relative motion of the body parts to change the operational status of the telephone set, e.g. switching on/off, answering incoming call
  • H04M1/0245—Portable telephones comprising a plurality of mechanically joined movable body parts, e.g. hinged housings using relative motion of the body parts to change the operational status of the telephone set, e.g. switching on/off, answering incoming call using open/close detection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M1/00—Substation equipment, e.g. for use by subscribers
  • H04M1/02—Constructional features of telephone sets
  • H04M1/23—Construction or mounting of dials or of equivalent devices; Means for facilitating the use thereof

Definitions

• the present invention relates generally to resistive ladder switching matrices. More particularly, the present invention relates to resistive ladder switching matrices used for operating keypads in portable electronic devices such as, for example, mobile telephones. Even more particularly, the present invention relates to a method and apparatus for calibrating resistive ladder switching matrices so as to compensate for variations in operating parameters such as temperature and oxidation on the keypad contacts connecting the keypad resistive ladder to the processing circuitry in the portable electronic device.
• Resistive ladder switching matrices are well known in the art, and are typically used for operating keypads in electronic devices. In such systems, depression of a button on the keypad completes the electrical connection of one or more resistors between a reference voltage and ground such that a unique voltage is produced at the output of the matrices in response to the depression of each button on the keypad.
• a microprocessor can determine which button a user has depressed on the keypad.
• Electronic devices such as certain cellular telephones (known as 'flip- phones') and laptop computers have moveable covers that are opened and closed.
• the keypad used with the resistive ladder network may itself be positioned on the moveable cover such that keypad will be exposed and active when the cover is closed and "hidden” and inactive when the cover is in its open position. It would be particularly desirable if there were a system that could be used for calibrating resistive ladder networks which was adaptable for use with electronic devices such as flip-phones and laptop computers having moveable covers.
• the present invention is directed to a method and apparatus for calibrating a resistive ladder switching matrix coupled to a keypad in a portable electronic device having a housing with a cover that may be positioned in an open state or a closed state.
• a first contact of a calibration element is coupled to a reference voltage and a second contact of the calibration element is coupled to ground by moving the cover from the open state to the closed state.
• a calibration resistance across the calibration element is determined.
• the calibration resistance corresponds to an input impedance of the resistive ladder switching matrix when no buttons associated with the keypad are depressed. Signals from the resistive ladder switching network are calibrated when the cover is in the closed state in accordance with the calibration resistance.
• Figure 1 is a block diagram showing a system for calibrating a resistive ladder switching matrix in accordance with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIG. 1 there is a block diagram showing a system 100 for calibrating a resistive ladder switching matrix 110 in accordance with the present invention.
• the present invention is used for calibrating a switching matrix disposed upon cover 120 of a mobile cellular flip phone, although it will be understood by those skilled in the art that the present invention could be employed in connection with other electronic devices such as laptop computers that also use moveable covers which open and close.
• Moveable cover 120 preferably includes a keypad and is pivotally coupled to the base 130 of the flip-phone by a mechanical hinge (not shown). The mechanical hinge permits the cover 120 to pivot or rotate between an open position and a closed position.
• the keypad is preferably positioned on the exterior of the cover 120 such that the keypad is exposed to a user and active when the cover is in the closed state and contacts 140 and 142 are closed.
• Electrical contacts 140 and 142 are coupled to terminals 144, 144a, 146 and 146a on the moveable cover 120 and base 130, and the relative position of contacts 140 and 142 varies as the moveable cover 120 pivots with respect to the base 130.
• both of the contacts 140 are electrically joined together and both of the contacts 142 are electrically joined together.
• both of the contacts 140 are electrically separated from each other, and both of the contacts 142 are separated from each other.
• contacts 140 function to electrically couple terminal 144 to terminal 144a when the moveable cover 120 is moved into its closed position
• contacts 142 function to electrically coupled terminal 146 to terminal 146a when the moveable cover 120 is moved into its closed position.
• contacts 140 are separated and contacts 142 are separated, thereby resulting in the disconnection of terminal 144 from terminal 144a, and the disconnection of terminal 146 from terminal 146a.
• the switches Sj, S 2 ... S N in the ladder matrix 110 are coupled to and actuated by the buttons (not shown) on the phone keypad located on cover 120.
• the moveable cover 120 When the moveable cover 120 is in the closed position, one or more of the resistors R R 2 ... R N in the ladder matrix will be selectively coupled to the reference voltage through ground upon depression of one of the switches S u S 2 ... S N .
• depression of one of the buttons on the keypad will cause a unique voltage associated with the depressed button to be provided to analog-to-digital converter 150, and then to microprocessor 160.
• the microprocessor 160 Based on the amplitude of the voltage signal supplied to the microprocessor 160, the microprocessor then identifies the button that has been depressed on the keypad. As mentioned in the background, the amplitude of these voltage signals will vary as a result of temperature changes and oxidation on the contacts 140 and 142.
• the present invention further includes a calibration element 115 which, as shown in Figure 1, can be modeled as a resistor (R CA ) that will have one terminal connected to the reference voltage and one terminal connected to ground when the cover 120 is in its closed position.
• the calibration element does not correspond to a physical resistor as shown in Figure 1, but instead simply represents a resistance that corresponds to the input impedance of the resistive ladder switching matrix 110 when no buttons associated with the keypad are depressed.
• the calibration element 115 can also include a physical resistor and, in such cases, the total resistance of the calibration element 115 will be equal to the resistance of the physical resistor plus a resistance that corresponds to the input impedance of the resistive ladder switching matrix 110 when no buttons associated with the keypad are depressed.
• the calibration element 115 supplies a voltage to the analog- to-digital converter 150, and finally to microprocessor 160.
• the microprocessor 160 determines a calibration resistance that corresponds to the resistance of calibration element 115.
• changes in this calibration resistance can be used to track variations that appear in the ladder network over time as a result of temperature changes and oxidation of the contacts 140 and 142. Since the terminals of the calibration element 115 are connected to the reference voltage and ground through contacts 140 and 142, respectively, the terminals of the calibration element 115 will be disconnected from the reference voltage and ground when the cover is in its open position.
• the calibration resistance is initially measured and stored for reference ("the reference resistance").
• the reference resistance is again measured by, for example, opening the cover 120 and measuring the voltage supplied to ADC 150.
• the calibration resistance will correspond to the reference resistance plus some "additional resistance" due to wear on the contacts 140 and 142.
• the microprocessor 160 can determine the "additional resistance” that has been added into the circuit as a result of the wear on contacts 140 and 142. During subsequent operation of the ladder matrix, the microprocessor 160 uses this "additional resistance" value to adjust or calibrate the resistance received upon depression of the keypad buttons so as to compensate for changes in temperature or oxidation of the switch contacts.
• the microprocessor 160 performs this calibration by first subtracting the "additional resistance" from the measured resistance associated with depression of a keypad button, and once the "additional resistance" has been subtracted from the measured resistance received via the keypad button, the microprocessor 160 then attempts to associated that adjusted resistance with a particular button on the keypad by matching the adjusted resistance value against a look up table.
• the reference voltage is 3.3V.
• Figure 1 shows the calibration element 115 as a physical resistor, in the preferred embodiment, the resistance of the calibration element 115 actually corresponds to the equivalent resistance of all the elements of the mobile phone as measured across terminals 140 and 142 with all switches S lf S 2 ... S N open.
• the equivalent resistance (Rc AL ) of the calibration element is approximately 210K ⁇ .
• the values of R ⁇ through R N in this embodiment were selected to be compatible with the ability of the ADC 150 to discriminate between voltage levels while also keeping the values compatible with the remaining phone circuitry.
• R : was 1K ⁇
• R 2 o (R N ) was 261K ⁇
• R2 through R19 fell somewhere between those values.

Landscapes

• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Theoretical Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Telephone Set Structure (AREA)
• Push-Button Switches (AREA)
• Input From Keyboards Or The Like (AREA)
• Transmitters (AREA)
• Analogue/Digital Conversion (AREA)
• Coupling Device And Connection With Printed Circuit (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Telephone Function (AREA)

Priority Applications (8)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (12)

Cited By (1)

Families Citing this family (11)

Citations (5)

Family Cites Families (12)

• 1998
  • 1998-11-13 US US09/191,200 patent/US6178388B1/en not_active Expired - Lifetime
• 1999
  • 1999-11-12 RU RU2001116123/09A patent/RU2233539C2/ru not_active IP Right Cessation
  • 1999-11-12 CN CNB99815346XA patent/CN1168220C/zh not_active Expired - Fee Related
  • 1999-11-12 DE DE69923343T patent/DE69923343T2/de not_active Expired - Lifetime
  • 1999-11-12 AU AU16209/00A patent/AU767291B2/en not_active Ceased
  • 1999-11-12 CA CA002350579A patent/CA2350579C/en not_active Expired - Fee Related
  • 1999-11-12 HK HK02104161.3A patent/HK1042599B/zh not_active IP Right Cessation
  • 1999-11-12 AT AT99958942T patent/ATE287592T1/de not_active IP Right Cessation
  • 1999-11-12 KR KR1020017006055A patent/KR20010080446A/ko not_active Ceased
  • 1999-11-12 EP EP99958942A patent/EP1131891B1/en not_active Expired - Lifetime
  • 1999-11-12 JP JP2000583169A patent/JP4295924B2/ja not_active Expired - Fee Related
  • 1999-11-12 WO PCT/US1999/026853 patent/WO2000030263A1/en not_active Ceased

Patent Citations (5)

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