Object position detector

• US 5,914,465 A
• Filed: 09/02/1994
• Issued: 06/22/1999
• Est. Priority Date: 06/08/1992
• Status: Expired due to Term

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Allen, Timothy P., Gillespie, David, Miller, Robert J., Steinbach, Gunter
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US08/300,387
• Time in Patent Office: 1,754 Days
• Field of Search: 178/18, 178/19, 345/173, 345/174, 345/175, 345/176, 345/177, 345/178, 341/33, 341/34
• US Class Current: 178/18.06
• CPC Class Codes: G06F 1/1626 with a single-body enclosure integrating a flat display, e.g. Personal Digital Assistants [PDAs]
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A proximity sensor system includes a sensor matrix array having a characteristic capacitance on horizontal and vertical conductors connected to sensor pads. The capacitance changes as a function of the proximity of an object or objects to the sensor matrix. The change in capacitance of each node in both the X and Y directions of the matrix due to the approach of an object is converted to a set of voltages in the X and Y directions. These voltages are processed by digital circuitry to develop electrical signals representative of the centroid of the profile of the object, i.e, its position in the X and Y dimensions. Noise reduction and background level setting techniques inherently available in the architecture are employed.

Claims

1. A method for providing an electrical signal representative of the position of an object in a two dimensional plane, including the steps of:

providing a sensing plane including a matrix of conductors arranged as a plurality of rows and columns of spaced apart row conductive lines and column conductive lines, said sensing plane characterized by an inherent capacitance on the various ones of said row conductive lines and column conductive lines, said capacitance varying with the proximity of an object to said row and column conductors;

simultaneously developing a first set of digital signals proportional to the value of said capacitance for each of said row conductive lines when no object is located proximate to said sensing plane;

simultaneously developing a second set of digital signals proportional to the value of said capacitance for each column conductive lines when no object is located proximate to said sensing plane;

simultaneously developing a third set of digital signals proportional to the value of said capacitance for each of said row conductive lines when an object is located proximate to said sensing plane;

simultaneously developing a fourth set of digital signals proportional to the value of said capacitance for each column conductive lines when said object is located proximate to said sensing plane;

computing a first weighted average of the difference between said first set of digital signals and said third set of digital signals;

computing a second weighted average of the difference between said second set of digital signals and said fourth set of digital signals.

2. The method of claim 1, wherein the steps of simultaneously developing said first, second, third, and fourth sets of digital signals includes the steps of:

placing a first known voltage on each of said row lines and each of said column lines;

removing charge from each of said row lines and each of said column lines for a fixed time at a fixed current;

measuring and storing a first set of resultant voltages appearing on said row lines and said column lines after said fixed time has elapsed;

placing a second known voltage on each of said row lines and each of said column lines;

adding charge to each of said row lines and each of said column lines for said fixed time at said fixed current;

measuring and storing a second set of resultant voltages appearing on said row lines and said column lines after said fixed time has elapsed; and

averaging corresponding ones of said first and second sets of resultant voltages.

3. The method of claim 1 wherein the steps of computing said first and second weighted averages comprises the steps of:

computing a sum and a weighted sum of said first set of digital signals;

computing a sum and a weighted sum of said second set of digital signals;

computing a sum and a weighted sum of said third set of digital signals;

computing a sum and a weighted sum of said fourth set of digital signals;

computing a row numerator by subtracting said weighted sum of said first set of digital signals from said weighted sum of said third set of digital signals;

computing a row denominator by subtracting said sum of said first set of digital signals from said sum of said third set of digital signals;

dividing said row numerator by said row denominator to derive a row position digital signal representing the position of said object in a row dimension;

computing a column numerator by subtracting said weighted sum of said second set of digital signals from said weighted sum of said fourth set of digital signals;

computing a column denominator by subtracting said sum of said second set of digital signals from said sum of said fourth set of digital signals; and

dividing said column numerator by said column denominator to derive a column position digital signal representing the position of said object in a column dimension.

4. The method of claim 3 including the further steps of:

storing said sum and said weighted sum of said first and third set of digital signals as a stored sum and a stored weighted sum of said second and fourth sets of digital signals; and

using said stored sum and said stored weighted sum in computing subsequent ones of said row numerators and denominators and said column numerators and denominators

using said stored stored sum and a stored weighted sum for providing an electrical signal representative of a subsequent position of said object in said two dimensional plane.