Method and apparatus for noise filtering for an input device

• US 5,825,351 A
• Filed: 11/15/1995
• Issued: 10/20/1998
• Est. Priority Date: 05/12/1994
• Status: Expired due to Term

• Current Assignee: Apple Computer Incorporated (Apple Inc.)
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Tam, Tommy H.
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): LEWIS, DAVID LEE
• Application Number:
  US08/559,258
• Time in Patent Office: 1,070 Days
• Field of Search: 345/156, 345/157, 345/159, 345/173, 345/174, 345/177, 178/18, 178/19
• US Class Current: 345/173
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• 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 method and apparatus in an electronically controlled system such as a portable computer are provided for minimizing effects of noise picked up by an input device such as a touch-sensitive capacitive coupling input pad where a conductive stylus may be used on the pad to control the cursor movement on a display device. The present invention removes the cursor jitters on the display device that is associated with the input device and provides for quick cursor responses corresponding to quick motion input by the conductive stylus on the input pad.

Claims

1. A computer system comprising:

a CPU for executing instructions and processing data;

a display subsystem coupled to said CPU wherein said display subsystem includes a display screen and a display driving circuit which receives and executes instructions from said CPU for moving a displayed marking on said display screen;

an input subsystem including an input pad for displayed marking movement information input by a user using a conductive stylus moving it against said input pad, said input pad having two conductive layers disposed on said input pad having a constant separation therebetween and said input pad having a pad circuit coupled to said input pad for determining location information of said conductive stylus on said input pad by repeatedly comparing measured capacitively-related values on selected portions of said input pad with reference values related to said selected portions of said input pad, said location information being in electronic and digital format and being representative of said marking movement information;

a noise filter coupled to said input subsystem and said CPU for receiving said location information, and for processing said location information for removing effects of noise picked up by said input subsystem whereby the noise filter is operatively sensitive to the speed of said conductive stylus and the noise filter generates and uses displacement information indicative of how far said conductive stylus had traveled in time for generating processed location information wherein a later piece of said processed location information is a function of an earlier piece of said processed location information and a selected proportion of said displacement information, the selected proportion used depending on the value of said displacement information, the processed location information being subsequently coupled to said display subsystem under the control of said CPU for moving said displayed marking on said display screen;

said two conductive layers being disposed on either side of said input pad, said layers further comprising;

a first array of conductive parallel strips electrically coupled to a driving circuit of said pad circuit for establishing capacitive values for said input pad;

a second array of conductive parallel strips disposed orthogonal to said first array, said second array of conductive strips being electrically coupled to a sensing circuit of said pad circuit for measuring said capacitive values for said input pad; and

wherein said driving circuit and said sensing circuit repeatedly select portions of said input pad for detecting and tracking capacitive aberration caused by said conductive stylus as it moves across said input pad, said capacitive aberration being related to the difference between said established capacitive values and said measured capacitive values;

said input pad being insulated and rigid to touch;

said noise filter generating and using displacement information indicative of how far said conductive stylus had traveled in time for generating said processed location information, said noise filter further generating a later piece of said processed location information by incorporating a proportion of said displacement information into an earlier piece of said processed location information, said noise filter further using a number of values for said proportion of said displacement information, a use of any particular value out of said number of values depending on the value of said displacement information;

wherein said later piece of said processed location information, X_later and Y_later, are derived according to the following rules;

X_later =X_earlier +(Δ

X/2ⁿ) and

Y_later =Y_earlier +(Δ

Y/2ⁿ)

where n >

0, Δ

X is the value of said displacement information in time in the X direction and Δ

Y is the value of said displacement information in time in the Y direction and where both Δ

X and Δ

Y are less than A, a number equal to or below which indicating said conductive stylus moving across said input pad slowly; and

X_later =X_earlier +(Δ

X/2^m) and

Y_later =Y_earlier +(Δ

Y/2^m)

where m ≧

0 and n >

m, and where Δ

X or Δ

Y is greater than A, a number over which indicating said conductive stylus moving across said input pad quickly.

2. An electronic apparatus comprising:

a CPU;

a subsystem of said electronic apparatus operatively coupled to said CPU wherein said subsystem receives and executes instructions from said CPU;

an input subsystem of said electronic apparatus including an input pad for instruction information input by a user using a conductive stylus moving it against said input pad, said input pad having two conductive layers disposed on said input pad having a constant separation therebetween, and said input pad having a pad circuit coupled to said input pad for determining location information of said conductive stylus on said input pad by comparing measured capacitively-related values on selected portions of said input pad with reference values related to said selected portions of said input pad, wherein said location information being in electronic and digital format and being representative of said user-input instruction information;

a noise filter coupled to said input subsystem and said CPU for receiving said location information, for providing displacement information indicative of how far said conductive stylus had traveled in time on said input pad and for processing said location information for removing effects of noise pickup by said input subsystem;

wherein said noise filter generates a later piece of said processed location information by incorporating a proportion of said displacement information into an earlier piece of said processed location information and that the value of said proportion depends on value of said displacement information;

further wherein said noise filter generates processed location information which is coupled to said subsystem for execution of said user-input instruction information;

said two conductive layers being disposed on either side of said input pad, said layers further comprising;

a first array of conductive parallel strips electrically coupled to a driving circuit of said pad circuit for establishing capacitive values for said input pad;

a second array of conductive parallel strips disposed orthogonal to said first array, said second array of conductive strips being electrically coupled to a sensing circuit of said pad circuit for measuring said capacitive values for said input pad; and

wherein said driving circuit and said sensing circuit repeatedly select portions of said input pad for detecting and tracking capacitive aberration caused by said conductive stylus as it moves across said input pad, said capacitive aberration being related to the difference between said established capacitive values and said measured capacitive values;

wherein said later piece of said processed location information, X_later and Y_later, are derived according to the following rules;

X_later =X_earlier +(Δ

X/2ⁿ) and

Y_later =Y_earlier +(Δ

Y/2ⁿ)

where n >

0, Δ

X is the value of said displacement information in time in the X direction and Δ

Y is the value of said displacement information in time in the Y direction and where both Δ

X and Δ

Y are less than A, a number equal to or below which indicating said conductive stylus moving across said input pad slowly; and

X_later =X_earlier +(Δ

X/2^m) and

Y_later =Y_earlier +(Δ

Y/2^m)

where m ≧

0 and n >

m, and where Δ

X or Δ

Y is greater than A, a number over which indicating said conductive stylus moving across said input pad quickly.

3. The electronic apparatus in claim 2 wherein said input subsystem is a stand alone unit.