Method and system for noise reduction for digitizing devices

• US 5,889,511 A
• Filed: 01/17/1997
• Issued: 03/30/1999
• Est. Priority Date: 01/17/1997
• Status: Expired due to Term

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Tritech Microelectronics International Pte LTD
• Inventors: Lim, Swee Hock Alvin, Ong, Eng Yue, Geng, Xia
• Primary Examiner(s): Luu, Matthew
• Application Number:
  US08/785,629
• Time in Patent Office: 802 Days
• Field of Search: 345/156, 345/157, 345/173, 345/174, 345/175, 178/18, 178/19
• US Class Current: 345/173
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

Systems and methods for the detection of motions of a pointed object upon a writing surface such as a touchpad are disclosed. The motions will be detected and converted in an analog-to-digital converter to digital codes representing the location of the pointed object upon the touchpad. The motion will be translated into a pen detect signal indicating the presence of the pointed object upon the touchpad. The digital codes will be filtered to minimize noise and formed into a filtered absolute coordinates digital code. The filtered absolute coordinate digital code and the pen detect signal will be converted to a touchpad-computer interface protocol and transferred to a computer system for further processing.

Claims

1. A touchpad digitizing computer input device to detect a presence of a pointed object upon a surface of said touchpad computer input device and converting said presence to a set of digital codes that indicate absolute location of said pointed object upon said surface, comprising:

a) a touchpad digitizer having a hard covering surface and a touch input transducer to convert said presence to electrical responses proportional to a distance of said pointed object from peripheral sides of said hard covering surface;

b) a touchpad driver circuit connected to said touchpad digitizer to provide an electrical stimulus to said touch input transducer;

c) an analog-to-digital converter to accept a plurality of analog signals including the electrical responses and the pressure analog signal, and convert at regular periodic intervals of time said plurality of analog signals to a plurality of digital codes that include a set of location digital codes representing the location of the pointed object upon the surface;

d) a pen detect circuit that receives said electrical responses to create a pen detect signal when said pointed object has been placed upon said touchpad digitizer;

e) an absolute coordinate calculator to convert the location digital codes to the absolute location digital codes that represent the location of the pointed object upon the touchpad digitizer;

f) an absolute coordinate filter means to filter the absolute location digital codes to create filtered absolute location digital codes that remove random and vibratory motions of the pointed object upon the touchpad digitizer and electrical noise induced to said touchpad digitizing computer input device from external sources, to create a smooth change of position indication of said absolute location digital codes;

g) an absolute coordinate code converter connected to the absolute coordinate filter means to convert the filtered absolute location digital codes to a touchpad computer interface protocol that is acceptable by the computer system; and

h) a touchpad computer interface to receive and convert the touchpad computer interface protocol and the pen detect signal, to buffer said touchpad computer interface protocol and said pen detect signal, and to convert said touchpad computer interface protocol and said pen detect signal to electrical signal levels that conform to the electrical specifications required of a interface between the touchpad-computer interface and the computer system to the computer system for further processing.

2. The input device of claim 1 wherein the electrical responses varies in magnitude according to the location of said pointed object upon said touchpad.

3. The input device of claim 1 wherein the pointed object is selected from the set of pointed objects including a human finger, a stylus, and a pen.

4. The input device of claim 1 wherein the electrical response selected from the set of electrical responses that include a change in voltage, a change in current, and a change in frequency of an oscillating signal.

5. The input device of claim 1 wherein filtering the absolute location digital codes is accomplished by a filtering process selected from the set of filtering processes comprising a thresholding process and an infinite impulse response filtering process, wherein:

a) the infinite impulse response filtering process comprises the steps of;

if there are no previous running average absolute location digital codes, the present absolute location digital codes are assigned to previous running average absolute location digital codes,

calculating a running average absolute location digital codes by adding the previous running average absolute location digital codes to the present absolute location digital codes and dividing a resulting sum by two to create current running average absolute location digital codes, and

placing the current running average absolute location digital codes in the filtered absolute location digital codes and the previous running average absolute location digital codes; and

b) the thresholding process comprises the steps of;

accepting for processing present absolute location digital codes, if the present absolute location digital codes have changed from previous absolute location digital codes by a magnitude greater than an initial movement threshold to indicate that the pointed object is intended to move,

accepting for processing the present absolute location digital codes if present absolute location digital codes have changed from previous absolute location digital codes by a magnitude greater than an intentional movement threshold if the pointed object is moving in a direction that is identical to that when said pointed object traversed the initial movement threshold,

accepting for processing the present absolute location digital codes if present absolute location digital codes have changed from previous absolute location digital codes by a magnitude less than an excess difference threshold that indicates the absolute location digital codes is to large and not a valid absolute location digital codes,

if the present absolute location digital codes are not accepted for processing, placing the previous absolute location digital codes in the filtered absolute location digital codes, and

if the present absolute location digital codes are not accepted for processing, placing said present absolute location digital codes in the filtered absolute location digital codes.

6. The input device of claim 1 wherein the absolute coordinate filter means comprises:

a) a current input register to receive at the regular periodic intervals of time the absolute location digital codes and to retain said absolute location digital codes;

b) a previous input register to retain a previous absolute location digital codes;

c) a subtractor circuit to subtract current input register from the previous input register to form a difference movement digital code;

d) a difference movement register connected to the subtractor to receive the difference movement digital code;

e) an initial movement comparator to compare the difference movement register to the initial movement threshold;

f) an intentional movement comparator to compare the difference movement register to the intentional movement threshold;

g) an excess difference comparator to compare the difference movement register to the excess difference threshold;

h) an output register to retain the filtered absolute location digital codes for transfer to the absolute location code converter;

i) a pen down indicator means to retain an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

j) a filter control means that;

will set the previous input register to an initial value if the pen detect signal indicates the pointed object is not in contact with the touchpad digitizer,

will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling and will place said absolute location digital codes in the previous input register,

will place the absolute location digital codes in the current input register, if the pen detect signal indicates the pointed object is in contact with the touchpad digitizer,

will discard current absolute location digital codes from the input register and place the previous absolute location digital codes from the previous input register in the output register, if the initial movement comparator indicates the difference movement register is less than the initial movement threshold and said intentional movement threshold, and greater than said excess difference threshold,

will place current absolute location digital codes from the input register in the output register if the initial movement comparator indicates the difference movement register is greater than the initial movement threshold and said intentional movement threshold, and less than said excess difference threshold, and

will set the previous input register to an initial value if the pen detect signal indicates that the pointed object is not in contact with the touchpad digitizer.

7. The input device of claim 1 wherein the absolute coordinate filter means comprises:

a) a current input register to receive at the regular periodic intervals of time the absolute location digital codes and to retain said absolute location digital codes;

b) a previous input register to retain a previous absolute location digital codes;

c) a running average register to retain the running average absolute location digital codes for next average calculations;

d) an adder to sum the input register to the running average register;

e) a divider to divide the sum of the input register and the running average register by a factor of two to create a next running average absolute location digital codes;

f) an output register to retain and transfer the next running average absolute location digital codes as the filtered absolute location digital codes for transfer to the absolute coordinate code converter;

g) a pen down indicator means to retain an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

h) a filter control means that;

will set the previous input register to an initial value if the pen detect signal indicates the pointed object is not in contact with the touchpad digitizer,

will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling and will place said absolute location digital codes in the previous input register and said running average register,

will place the absolute location digital codes in the current input register, if the pen detect signal indicates the pointed object is in contact with the touchpad digitizer,

will replace the running average absolute location digital codes in the running average register with the current absolute location digital codes from the input register the previous input register has been set to the initial digital code, and

will copy the next running average absolute location digital codes to the running average register from the output register for a next processing of a next sample of the absolute location digital codes, when the adder has summed the contents of the input register and the running average register and results have been divided by two in the divider to for the next running average digital codes.

8. The input device of claim 5 wherein the absolute coordinate filter means comprises:

a) a current input register to receive at the regular periodic intervals of time the absolute location digital codes and to retain said absolute location digital codes;

b) a previous input register to retain a previous absolute location digital codes;

c) a mode select register to retain a mode select code wherein said mode select code comprises;

a no filter code that commands said absolute coordinate filter means to perform no filtering and pass the current input register to the output register,

a threshold filter code that will command said absolute coordinate filter means to perform the thresholding filter process,

a infinite impulse response filter code that will command said absolute coordinate filter means to perform the infinite impulse response filter process, and

a threshold filter/infinite impulse response code that will command said absolute coordinate filter means to perform both the thresholding filter process and the infinite impulse response filter process;

d) a subtractor circuit to subtract current input register from the previous input register to form a difference movement digital code;

e) a difference movement register connected to the subtractor to receive the difference movement digital code;

f) an initial movement comparator to compare the difference movement register to the initial movement threshold;

g) an intentional movement comparator to compare the difference movement register to the intentional movement threshold;

h) an excess difference comparator to compare the difference movement register to the excess difference threshold;

i) a running average register to retain the running average absolute location digital codes for next average calculations;

j) an adder to sum the input register to the running average register;

k) a divider to divide the sum of the input register and the running average register by a factor of two to create a next running average absolute location digital codes;

l) an output register to retain and transfer the next running average absolute location digital codes to the absolute coordinate code converter;

m) a pen down indicator means to retain an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

n) a filter control means that

will set the previous input register to an initial value if the pen detect signal indicates the pointed object is not in contact with the touchpad digitizer,

will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling and will place said absolute location digital codes in the previous input register and said running average register,

will place the absolute location digital codes in the current input register, if the pen detect signal indicates the pointed object is in contact with the touchpad digitizer,

if the mode select register contains an thresholding filter

code, will discard current absolute location digital codes from the input register and place the previous absolute location digital codes from the previous input register in the output register, if the initial movement comparator indicates the difference movement register is less than the initial movement threshold and said intentional movement threshold, and greater than said excess difference threshold,

will place current absolute location digital codes from the input register in the output register if the initial movement comparator indicates the difference movement register is greater than the initial movement threshold and said intentional movement threshold, and less than said excess difference threshold,

if the mode select register contains a infinite impulse

response filter code, will replace the running average absolute location digital codes in the running average register with the current absolute location digital codes from the input register the previous input register has been set to the initial digital code, and

will copy the next running average absolute location digital codes to the running average register from the output register for a next processing of a next sample of the absolute location digital codes, when the adder has summed the contents of the input register and the running average register and results have been divided by two in the divider to for the next running average digital codes.

9. A digitizer/computer input device control circuit to accept electrical response signals generated by a pointed object in contact with a digitizing surface such as touchpad digitizer, and to create a pen-input protocol if a pen-input mode is selected and to create a computer input mouse protocol having a running average absolute location digital codes that will minimize vibration and noise present in the electrical response signals for transmission to a computer system for further processing, comprising:

a) a digitizer driver circuit connected to said digitizing surface to provide an electrical stimulus to said digitizing surface;

b) an analog-to-digital converter to accept a plurality of analog signals including the electrical responses and the pressure analog signal, and convert at regular periodic intervals of time said plurality of analog signals to a plurality of digital codes that include a set of location digital codes representing the location of the pointed object upon the surface;

c) a pen detect circuit that receives said electrical responses to create a pen detect signal when said pointed object has been placed upon said digitizing surface;

d) an absolute coordinate calculator to convert the location digital codes to the absolute location digital codes that represent the location of the pointed object upon the digitizing surface;

e) an absolute coordinate filter means to filter the absolute location digital codes to create the running average absolute location digital codes that remove random and vibratory motions of the pointed object upon the touchpad digitizer and electrical noise induced to said touchpad digitizing computer input device from external sources, to create a smooth change of position indication of said absolute location digital codes;

f) an absolute coordinate code converter connected to the absolute coordinate filter means to convert the running average absolute location digital codes to a touchpad computer interface protocol that is acceptable by the computer system; and

g) a touchpad computer interface to receive and convert the touchpad computer interface protocol and the pen detect signal to buffer said touchpad computer interface protocol and said pen detect signal and convert said touchpad computer interface protocol and said pen detect signal to electrical signal levels that conform to the electrical specifications required of a interface between the touchpad-computer interface and the computer system to the computer system for further processing.

10. The input device of claim 9 wherein filtering the absolute location digital codes is accomplished by a filtering process selected from the set of filtering processes comprising a thresholding process and an infinite impulse response filtering process, wherein:

a) the thresholding process comprises the steps of;

accepting for processing present absolute location digital codes, if the present absolute location digital codes have changed from previous absolute location digital codes by a magnitude greater than an initial movement threshold to indicate that the pointed object is intended to move,

accepting for processing the present absolute location digital codes if present absolute location digital codes have changed from previous absolute location digital codes by a magnitude greater than an intentional movement threshold if the pointed object is moving in a direction that is identical to that when said pointed object traversed the initial movement threshold,

accepting for processing the present absolute location digital codes if present absolute location digital codes have changed from previous absolute location digital codes by a magnitude less than an excess difference threshold that indicates the absolute location digital codes is to large and not a valid absolute location digital codes,

if the present absolute location digital codes are not accepted for processing, placing the previous absolute location digital codes in the filtered absolute location digital codes, and

if the present absolute location digital codes are not accepted for processing, placing said present absolute location digital codes in the filtered absolute location digital codes; and

b) the infinite impulse response filtering process comprises the steps of;

if there are no previous running average absolute location digital codes, the present absolute location digital codes are assigned to previous running average absolute location digital codes,

calculating a running average absolute location digital codes by adding the previous running average absolute location digital codes to the present absolute location digital codes and dividing a resulting sum by two to create current running average absolute location digital codes, and

placing the current running average absolute location digital codes in the filtered absolute location digital codes and the previous running average absolute location digital codes.

11. The input device of claim 9 wherein the absolute coordinate filter means comprises:

a) a current input register to receive at the regular periodic intervals of time the absolute location digital codes and to retain said absolute location digital codes;

b) a previous input register to retain a previous absolute location digital codes;

c) a subtractor circuit to subtract current input register from the previous input register to form a difference movement digital code;

d) a difference movement register connected to the subtractor to receive the difference movement digital code;

e) an initial movement comparator to compare the difference movement register to the initial movement threshold;

f) an intentional movement comparator to compare the difference movement register to the intentional movement threshold;

g) an excess difference comparator to compare the difference movement register to the excess difference threshold;

h) an output register to retain the filtered absolute location digital codes for transfer to the absolute location code converter;

i) a pen down indicator means to retain an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

j) a filter control means that;

will set the previous input register to an initial value if the pen detect signal indicates the pointed object is not in contact with the touchpad digitizer,

will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling and will place said absolute location digital codes in the previous input register,

will place the absolute location digital codes in the current input register, if the pen detect signal indicates the pointed object is in contact with the touchpad digitizer,

will discard current absolute location digital codes from the input register and place the previous absolute location digital codes from the previous input register in the output register, if the initial movement comparator indicates the difference movement register is less than the initial movement threshold and said intentional movement threshold, and greater than said excess difference threshold,

will place current absolute location digital codes from the input register in the output register if the initial movement comparator indicates the difference movement register is greater than the initial movement threshold and said intentional movement threshold, and less than said excess difference threshold, and

will set the previous input register to an initial value if the pen detect signal indicates that the pointed object is not in contact with the touchpad digitizer.

12. The input device of claim 9 wherein the absolute coordinate filter means comprises:

a) a current input register to receive at the regular periodic intervals of time the absolute location digital codes and to retain said absolute location digital codes;

b) a previous input register to retain a previous absolute location digital codes;

c) a running average register to retain the running average absolute location digital codes for next average calculations;

d) an adder to sum the input register to the running average register;

e) a divider to divide the sum of the input register and the running average register by a factor of two to create a next running average absolute location digital codes;

f) an output register to retain and transfer the next running average absolute location digital codes as the filtered absolute location digital codes for transfer to the absolute coordinate code converter;

g) a pen down indicator means to retain an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

h) a filter control means that;

will set the previous input register to an initial value if the pen detect signal indicates the pointed object is not in contact with the touchpad digitizer,

will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling and will place said absolute location digital codes in the previous input register and said running average register,

will place the absolute location digital codes in the current input register, if the pen detect signal indicates the pointed object is in contact with the touchpad digitizer,

will replace the running average absolute location digital codes in the running average register with the current absolute location digital codes from the input register the previous input register has been set to the initial digital code,

will copy the next running average absolute location digital codes to the running average register from the output register for a next processing of a next sample of the absolute location digital codes, when the adder has summed the contents of the input register and the running average register and results have been divided by two in the divider to for the next running average digital codes.

13. The input device of claim 9 wherein the absolute coordinate filter means comprises:

a) a current input register to receive at the regular periodic intervals of time the absolute location digital codes and to retain said absolute location digital codes;

b) a previous input register to retain a previous absolute location digital codes;

c) a mode select register to retain a mode select code wherein said mode select code comprises;

a no filter code that commands said absolute coordinate filter means to perform no filtering and pass the current input register to the output register,

a threshold filter code that will command said absolute coordinate filter means to perform the thresholding filter process,

a infinite impulse response filter code that will command said absolute coordinate filter means to perform the infinite impulse response filter process, and

a threshold filter/ infinite impulse response code that will command said absolute coordinate filter means to perform both the thresholding filter process and the infinite impulse response filter process;

d) a subtractor circuit to subtract current input register from the previous input register to form a difference movement digital code;

e) a difference movement register connected to the subtractor to receive the difference movement digital code;

f) an initial movement comparator to compare the difference movement register to the initial movement threshold;

g) an intentional movement comparator to compare the difference movement register to the intentional movement threshold;

h) an excess difference comparator to compare the difference movement register to the excess difference threshold;

i) a running average register to retain the running average absolute location digital codes for next average calculations;

j) an adder to sum the input register to the running average register;

k) a divider to divide the sum of the input register and the running average register by a factor of two to create a next running average absolute location digital codes;

l) an output register to retain and transfer the next running average absolute location digital codes to the absolute coordinate code converter;

m) a pen down indicator means to retain an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

n) a filter control means that

will set the previous input register to an initial value if the pen detect signal indicates the pointed object is not in contact with the touchpad digitizer,

will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling and will place said absolute location digital codes in the previous input register and said running average register,

will place the absolute location digital codes in the current input register, if the pen detect signal indicates the pointed object is in contact with the touchpad digitizer,

if the mode select register contains an thresholding filter

code, will discard current absolute location digital codes from the input register and place the previous absolute location digital codes from the previous input register in the output register, if the initial movement comparator indicates the difference movement register is less than the initial movement threshold and said intentional movement threshold, and greater than said excess difference threshold,

will place current absolute location digital codes from the input register in the output register if the initial movement comparator indicates the difference movement register is greater than the initial movement threshold and said intentional movement threshold, and less than said excess difference threshold,

if the mode select register contains a infinite impulse

response filter code, will replace the running average absolute location digital codes in the running average register with the current absolute location digital codes from the input register the previous input register has been set to the initial digital code, and

will copy the next running average absolute location digital codes to the running average register from the output register for a next processing of a next sample of the absolute location digital codes, when the adder has summed the contents of the input register and the running average register and results have been divided by two in the divider to for the next running average digital codes.

14. The control circuit of claim 9 wherein the electrical responses varies in magnitude according to the location of said pointed object upon said touchpad.

15. The control circuit of claim 9 wherein the pointed object is selected from the set of pointed objects including a human finger, a stylus, and a pen.

16. The control circuit of claim 9 wherein the electrical response selected from the set of electrical responses that include a change in voltage, a change in current, and a change in frequency of an oscillating signal.

17. A method to detect the placement of a pointed object upon a digitizing surface, to filter random vibration and noise from said detected placement, and to create filtered instantaneous location digital codes that are transferred to a computer system for further processing, comprising the steps of:

a) periodically sampling of electrical responses that result from the placement of the pointed object upon the digitizing surface, wherein magnitudes of said responses represent the location of said pointed object upon said digitizing surface;

b) converting said electrical responses in an analog-to-digital converter to a set of location digital codes representing the magnitudes of the electrical responses;

c) calculating from said location digital codes, an instantaneous location digital codes representing an instantaneous placement of said pointed object upon said digitizing surface;

d) accepting for processing present instantaneous location digital codes, if the present instantaneous location digital codes have changed from previous instantaneous location digital codes by a magnitude greater than an initial movement threshold to indicate that the pointed object is intended to move;

e) accepting for processing the present instantaneous location digital codes if present instantaneous location digital codes have changed from previous instantaneous location digital codes by a magnitude greater than an intentional movement threshold if the pointed object is moving in a direction that is identical to that when said pointed object traversed the initial movement threshold;

f) accepting for processing the present instantaneous location digital codes if present instantaneous location digital codes have changed from previous instantaneous location digital codes by a magnitude less than an excess difference threshold that indicates the instantaneous location digital codes is to large and not a valid instantaneous location digital codes;

g) if the present instantaneous location digital codes are not accepted for processing, placing the previous instantaneous location digital codes in the filtered instantaneous location digital codes;

h) if the present instantaneous location digital codes are not accepted for processing, placing said present instantaneous location digital codes in the filtered instantaneous location digital codes;

i) converting said filtered instantaneous location digital codes to a protocol acceptable by said computer system;

j) transferring said protocol of the new running average instantaneous location digital codes to said computer system;

k) retaining the current instantaneous location digital codes as the previous instantaneous location digital codes; and

l) reiterating the aforementioned steps to create a series of filtered instantaneous location digital codes representing motion of the pointed object upon the digitizing surface.

18. The method of claim 17 further comprising the steps of:

a) examining a pen detect signal that signifies the presence or absence of the pointed object upon the digitizing surface;

b) if the pen detect signal indicates the presence of the pointed object on the digitizing surface, proceeding to the periodic sampling of the electrical responses; and

c) if the pen detect signal indicates the absence of the pointed object on the digitizing surface, setting the previous instantaneous location digital codes to the initial value and then proceeding with the periodic sampling.

19. The method of claim 17 further comprising the steps of;

a) examining a pen down indicator means that retains an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

b) will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling; and

c) will place said absolute location digital codes in the previous input register.

20. A method to detect the placement of a pointed object upon a digitizing surface, to filter random vibration and noise from said detected placement, and to create filtered instantaneous location digital codes that are transferred to a computer system for further processing, comprising the steps of:

a) periodically sampling of electrical responses that result from the placement of the pointed object upon the digitizing surface, wherein magnitudes of said responses represent the location of said pointed object upon said digitizing surface;

b) converting said electrical responses in an analog-to-digital converter to a set of location digital codes representing the magnitudes of the electrical responses;

c) calculating from said location digital codes, an instantaneous location digital codes representing an instantaneous placement of said pointed object upon said digitizing surface;

d) if there are no previous running average instantaneous location digital codes, the present instantaneous location digital codes are assigned to previous running average instantaneous location digital codes;

e) calculating a running average instantaneous location digital codes by adding the previous running average instantaneous location digital codes to the present instantaneous location digital codes and dividing a resulting sum by two to create current running average instantaneous location digital codes; and

f) placing the current running average instantaneous location digital codes in the filtered instantaneous location digital codes and the previous running average instantaneous location digital codes.

g) converting said filtered instantaneous location digital codes to a protocol acceptable by said computer system;

h) transferring said protocol of the new running average instantaneous location digital codes to said computer system;

i) retaining the current instantaneous location digital codes as the previous instantaneous location digital codes; and

j) reiterating the aforementioned steps to create a series of filtered instantaneous location digital codes representing motion of the pointed object upon the digitizing surface.

21. The method of claim 20 further comprising the steps of:

a) examining a pen detect signal that signifies the presence or absence of the pointed object upon the digitizing surface;

b) if the pen detect signal indicates the presence of the pointed object on the digitizing surface, proceeding to the periodic sampling of the electrical responses; and

c) if the pen detect signal indicates the absence of the pointed object on the digitizing surface, setting the previous instantaneous location digital codes to the initial value and then proceeding with the periodic sampling.

22. The method of claim 20 further comprising the steps of;

a) examining a pen down indicator means that retains an indication that a current sampling of said absolute location digital codes are a first sampling of the absolute location digital codes;

b) will set said pen down indicator means to a true value if said current sampling of said absolute location digital codes are said first sampling; and

c) will place said absolute location digital codes in the previous input register and said running average register.

23. A touchpad digitizing computer input device with noise reduction comprising:

a) a touchpad digitizer having a surface upon which a pointed object is used;

b) a means for providing absolute location digital codes representing a location of the pointed object on the touchpad digitizer;

c) an absolute coordinate threshold filtering means to filter location digital codes to create a filtered absolute coordinate digital codes with remove noise, wherein said filtering means creates a smooth change of position indication;

by accepting for processing present absolute location digital codes, if the present absolute location digital codes have changed from previous absolute location digital codes by a magnitude greater than an initial movement threshold to indicate that the pointed object is intended to move,

by accepting for processing the present absolute location digital codes if present absolute location digital codes have changed from previous absolute location digital codes by a magnitude greater than an intentional movement threshold if the pointed object is moving in a direction that is identical to that when said pointed object traversed the initial movement threshold,

by accepting for processing the present absolute location digital codes if present absolute location digital codes have changed from previous absolute location digital codes by a magnitude less than an excess difference threshold that indicates the absolute location digital codes is to large and not a valid absolute location digital codes,

if the present absolute location digital codes are not accepted for processing, by placing the previous absolute location digital codes in the filtered absolute location digital codes, and

if the present absolute location digital codes are not accepted for processing, by placing said present absolute location digital codes in the filtered absolute location digital codes; and

d) a means for converting the filtered average digital codes to a touchpad computer interface protocol for transmission to an attached computer system.

24. A touchpad digitizing computer input device with noise reduction comprising:

a) a touchpad digitizer having a surface upon which a pointed object is used;

b) a means for providing absolute location digital codes representing a location of the pointed object on the touchpad digitizer;

c) an absolute coordinate averaging filter means to filter location digital codes to create a filtered absolute coordinate digital codes with remove noise, wherein said filtering means creates a smooth change of position indication;

if there are no previous running average absolute location digital codes, by assigning the present absolute location digital codes to previous running average absolute location digital codes,

by calculating a running average absolute location digital codes by adding the previous running average absolute location digital codes to the present absolute location digital codes and dividing a resulting sum by two to create current running average absolute location digital codes, and

placing the current running average absolute location digital codes in the filtered absolute location digital codes and the previous running average absolute location digital codes; and

d) a means for converting the filtered average digital codes to a touchpad computer interface protocol for transmission to an attached computer system.