Frequency shifting digitizer for reducing AC fields interference
First Claim
1. In a digitizer wherein the position of a movable instrument on a digitizing surface is determined from voltages induced between one or more conductors disposed across the digitizing surface and an electrical element carried by a movable instrument at a transduction frequency established by a frequency source, the improvement for reducing interference caused by adjacent AC fields comprising:
- (a) counter means for receiving input pulses at a first input, for outputting output pulses employed to generate the transduction frequency source in the digitizer, and for receiving an initial count value at a second input, said counter means including logic for repeatedly counting from said initial count value at said second input to a terminal value, for outputting a said output pulse upon reaching said terminal value, and for resetting to said initial count value after outputting each said output pulse;
(b) a source of a higher frequency than the transduction frequency connected to said first input of said counter means; and
,(c) means for selectably setting said initial count value at said second input.
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Accused Products
Abstract
A digitizer wherein the transduction frequency is controlled (automatically or manually) to minimize the interference effect of sources of external AC fields, such as CRT monitors. The digitizer implements the method of operation comprising the steps of, connecting a source of a frequency higher than the frequency to be employed as the transduction frequency of the digitizer to the first input of a counter; receiving input pulses from the source at the first input of the counter; outputting output pulses which are employed to generate the transduction frequency in the digitizer at an output of the counter; selectively setting an initial count value at a second input of the counter; and, repeatedly counting from the initial count value at the second input to a terminal value, outputting an output pulse upon reaching the terminal value, and resetting to the initial count value after outputting each output pulse. The preferred automated method includes reading and saving the induced position voltages being employed by the digitizer, testing the saved voltages for any flutter, and setting the initial count value to an optimum level.
36 Citations
15 Claims
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1. In a digitizer wherein the position of a movable instrument on a digitizing surface is determined from voltages induced between one or more conductors disposed across the digitizing surface and an electrical element carried by a movable instrument at a transduction frequency established by a frequency source, the improvement for reducing interference caused by adjacent AC fields comprising:
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(a) counter means for receiving input pulses at a first input, for outputting output pulses employed to generate the transduction frequency source in the digitizer, and for receiving an initial count value at a second input, said counter means including logic for repeatedly counting from said initial count value at said second input to a terminal value, for outputting a said output pulse upon reaching said terminal value, and for resetting to said initial count value after outputting each said output pulse; (b) a source of a higher frequency than the transduction frequency connected to said first input of said counter means; and
,(c) means for selectably setting said initial count value at said second input. - View Dependent Claims (2)
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3. An improved digitizer employing induced voltages and having reduced interference caused by adjacent AC fields comprising:
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(a) a frequency source of a frequency higher than the frequency to be employed as a transduction frequency in the digitizer; (b) a movable instrument including an electrical element; (c) a tablet having a digitizing surface with one or more conductors disposed across the digitizing surface; (d) means for determining the position of said movable instrument on said digitizing surface from voltages induced between said conductors and said electrical element at a transduction frequency; (e) counter means for receiving input pulses at a first input, for outputting output pulses employed to generate said transduction frequency, and for receiving an initial count value at a second input, said counter means including logic for repeatedly counting from said initial count value at said second input to a terminal value, for outputting a said output pulse upon reaching said terminal value, and for resetting to said initial count value after outputting each said output pulse, said first input of said counter means being connected to said frequency source; and
,(f) means for selectably setting said initial count value at said second input. - View Dependent Claims (4)
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5. In a digitizer wherein the position of a movable instrument on a digitizing surface is determined from voltages induced between one or more conductors disposed across the digitizing surface and an electrical element carried by the movable instrument at a transduction frequency established by a frequency source, the improved method of operation for reducing interference caused by adjacent AC fields comprising the steps of:
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(a) connecting a source of a frequency higher than the transduction frequency to the first input of a counter; (b) receiving input pulses from the higher frequency source at the first input of the counter; (c) outputting output pulses which are employed to generate the transduction frequency source in the digitizer at an output of the counter; (d) selectively setting an initial count value at a second input of the counter; and
,(e) repeatedly counting from the initial count value at the second input to a terminal value, outputting an output pulse upon reaching the terminal value, and resetting to the initial count value after outputting each output pulse. - View Dependent Claims (6)
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7. In a digitizer wherein the position of a transducer on a digitizing surface is determined from voltage induced between one or more conductors disposed across the digitizing surface and an electrical element carried by a movable instrument at a transduction frequency established by a frequency source, the improvement for reducing interference caused by adjacent AC fields comprising:
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(a) a frequency source capable of producing a plurality of frequencies suitable for use as the transduction frequency; and
,(b) means for selecting the one of said frequencies to be employed as the transduction frequency including means for testing induced voltages for flutter and for employing as the transduction frequency the one of said frequencies which minimizes any flutter. - View Dependent Claims (8, 9)
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10. An improved digitizer employing induced voltages and having reduced interference caused by adjacent AC fields comprising:
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(a) a frequency source capable of producing a plurality of frequencies suitable for use as a transduction frequency; (b) a movable instrument including an electrical element; (c) a tablet having a digitizing surface with one or more conductors disposed across said digitizing surface; (d) means for determining the position of said movable instrument on said digitizing surface from voltages induced between said conductors and said electrical element at a transduction frequency; and
,(e) means for selecting the one of said frequencies to be employed as the transduction frequency including means for testing induced voltages for flutter and for employing as said transduction frequency the one of said frequencies which minimizes any flutter. - View Dependent Claims (11, 12)
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13. In a digitizer wherein the position of a movable instrument on a digitizing surface is determined from voltages induced between one or more conductors disposed across the digitizing surface and an electrical element carried by the movable instrument at a transduction frequency established by a frequency source, the improved method of operation for reducing interference caused by adjacent AC fields comprising the steps of:
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(a) providing a frequency source capable of producing a plurality of frequencies suitable for use as the transduction frequency; (b) testing induced voltages for flutter; and
,(c) employing as the transduction frequency the one of the plurality of frequencies which minimizes any flutter. - View Dependent Claims (14, 15)
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Specification