Noise eliminating circuit for a graphical input terminal

Claim 2

A noise eliminating circuit for a graphical input terminal having input means including a hand-operated stylus to write on an input surface, said input means generating an electrical indication corresponding to information written on said input surface by said hand-operated stylus, said input means also generating a first signal including information specifying at least a starting time of a writing operation on said surface, said noise eliminating circuit comprising: low-pass filter means coupled to receive said electrical indication; switch means for selecting either said electrical indication or the output signal from said low-pass filter means as an output signal of said noise eliminating circuit; control means which is responsive to the first signal including said starting time-specifying information to control said switch means for continuing said selection for a predetermined duration of time after said starting time; and means for changing said signal including the time-specifying information to a predetermined level only during the writing operation.

Claim 3

A noise eliminating circuit for a graphical input terminal as claimed in claim 1, in which said control means includes a monostable multivibrator triggered by said signal including said time-specifying information at said starting time to produce a pulse for said predetermined duration of time, and means including an exclusive OR gate circuit operating between said signal including said time point-specifying information and the output of said monostable multivibrator.

Claim 4

A noise eliminating circuit for a graphical input terminal as claimed in claim 1, in which said control means includes a first monostable multivibrator triggered by said signal including said time-specifying information at said starting time, said first multivibrator producing an output pulse for a first predetermined duration of time, said signal from said input means also indicating a terminating time of said writing operation, and a second monostable multivibrator triggered by said signal including said terminating time of said writing operation, said second multivibrator producing an output pulse for a second predetermined duration of time.

Claim 5

A noise eliminating circuit for a graphical input terminal having input means including a hand-operated stylus to write on an input surface, said input terminal giving a first signal which includes information specifying at least a starting time of a writing operation and thereafter continues as long as said stylus engages said surface so that said given first signal includes both said starting time-specifying information and also the terminating time of said writing operation, said stylus generating an electrical indication corresponding to information written on said input surface by said hand-operated stylus, said noise eliminating circuit comprising: low-pass filter means coupled to receive said electrical indication and to give an output signal; switch means for selecting either said electrical indication or the output signal from said low-pass filter means as an output signal of said noise eliminating circuit; control means which is responsive to the first signal including said starting time-specifying information to control said switch means for continuing said selection for a predetermined duration of time after said starting time; said control means being operated responsive to said given first signal including said starting time-specifying information to select said indication for a first predetermined duration of time after said starting time and a second predetermined duration of time after said terminating time; said control means further including a first monostable multivibrator triggered by said signal including said time-specifying information at said starting time, said first multivibrator producing a pulse for said first predetermined duration of time, and a second monostable multivibrator triggered by said signal including the time-specifying information at said terminating time, said second multivibrator producing a pulse for said second predetermined duration of time.

Claim 6

A noise eliminating circuit for a graphical input terminal having input means including a hand-operated stylus to write on an input surface, said input terminal giving a first signal which includes information specifying at least a starting time of a writing operation and thereafter continues as long as said stylus engages said surface so that said given first signal includes both said starting time-specifying information and also the terminating time of said writing operation, said stylus generating an electrical indication corresponding to information written on said input surface by said hand-operated stylus, said noise eliminating circuit comprising: low-pass filter means coupled to receive said electrical indication and to give an output signal; switch means for selecting either said electrical indication or the output signal from said low-pass filter means as an output signal of said noise eliminating circuit; control means which is responsive to the first signal including said starting time-specifying information to control said switch means for continuing said selection for a predetermined duration of time after said starting time; said control means being operated responsive to said given first signal including said starting time-specifying information to select said indication for a first predetermined duration of time after said starting time and a second predetermined duration of time after said terminating time; said control means further including a first monostable multivibrator triggered by said signal including said time-specifying information at said starting time, said first multivibrator producing a pulse for said first predetermined duration of time, and a second monostable multivibrator triggered by said signal including the time-specifying information at said terminating time, said second multivibrator producing a pulse for said second predetermined duration of time.