Abstract: A digitizing system includes a plurality of spaced parallel grid conductors embedded beneath a support surface. A movable pen coil powered by an amplifier induces AC signals in the grid conductors. The grid conductors are scanned at a first rate from a reference point to detect the approximate location of the pen coil. The grid conductors are then "up scanned" at a second rate toward the pen coil. As the scan counter is incremented, a pen position counter is simultaneously incremented at a third rate which is substantially greater than the second rate to effect interpolation between grid conductors. The up scanning is halted when a rectified and integrated waveform resulting from the up scanning operation undergoes a phase change. A first digital number contained in the pen position counter then is stored. The polarity of the signal driving the pen coil then is reversed. The grid conductors are then "down scanned" at the second rate toward the pen coil.

Abstract: A pen status indicating system for a digitizer pen utilized in conjunction with a digitizer having a grid of spaced conductors positioned beneath a writing surface. The digitizer includes an electronic system which scans the spaced conductors and senses signals produced in the spaced conductors by a transmitting coil located near the writing tip of a pen used to write on the writing surface. The pen status indicating system senses whether the writing tip of the pen is pressed against the writing surface. The pen status indicating system includes a split inductor having a movable core coupled in direct communication with a pen cartridge having the writing tip connected thereto.

Abstract: A low noise system and method are provided for sequentially sensing induced signals in a plurality of digitizer grid conductors. The digitizer includes a coil disposed above the tip of a pen. The coil induces the signals in the grid conductors. The system includes scanning circuitry which sequentially scans the grid conductors, which are oriented in an X direction and a Y direction, causing the induced signal to be sequentially coupled to the input of a differential amplifier. The X and Y grid conductors each have first ends connected to corresponding inputs of first and second multiplexers. The X and Y grid conductors each also have corresponding second ends connected to first and second corresponding common conductors. The outputs of the first and second multiplexers are coupled, respectively, to first and second inputs of the differential amplifier. The first and second common conductors are coupled, respectively, to the outputs of the second and first multiplexers.