Low-cost, high-accuracy digitizer signal acquisition apparatus and method

Abstract

An improvement to position digitizing devices wherein sensed response voltages caused by the interaction of a movable instrument relative to conductors beneath a planar surface are converted to digital form and digitally processed to determine instrument position. An integrating voltage to frequency converter is used to produce a frequency with a correspondence to the voltage applied to it. By counting the frequency for a defined length of time, a resultant count is obtained which also corresponds to the applied voltage. By varying the counting period under microprocessor control, acquisition rate and resolution can be varied over several orders of magnitude without changing circuit components. The digitizer includes conductive elements disposed across the digitizing surface and incorporated into an instrument for producing an analog voltage signal having a DC component related to the position of the instrument on the digitizing surface. There is a voltage to frequency converter for receiving the analog voltage signal and for converting it to a pulsed signal at a frequency which is a monotonically increasing or decreasing function of the voltage level of the analog voltage signal. There is a counter for receiving the pulsed signal from the voltage to frequency converter, for counting the pulses of the pulsed signal, and for producing a digital value output proportional to the counted pulses whereby the digital value is similarly related to the voltage level of the analog voltage signal.