Low power, high resolution digitizing system with cordless pen/mouse

DETAILED DESCRIPTION It is an object of the invention to provide a digitizing device including a cordless electrostatic stylus or cursor that is capacitively coupled to a digitizer surface.
It is another object of the invention to provide a cordless electrostatic digitizer stylus or cursor that also is capable of transmitting commands to a digitizer surface, which command signals are decoded and presented in a suitable format to a computing device.
It is another object of the invention to provide an inexpensive digitizing system that includes a cordless stylus or cursor, and which is operable at far lower power levels than any prior digitizing system.
It is another object of the invention to provide a computer input device that can function as a keyboard, a digitizer, or a mouse.
Briefly described, and in accordance with one embodiment thereof, the invention provides a digitizing system including a cordless pen containing an oscillator that generates a signal that is applied to a conductive stylus which is surrounded by a relatively massive conductive shield.
The shield has a large physical size that enables it to function as a good virtual ground and to minimize capactive coupling with the stylus.
The relative massiveness of the shield causes it to have much greater stray capacitance than the stylus.
This large stray capacitance, together with the small capacitive coupling to the stylus, results in the effective virtual ground and highly directional capacitive coupling from the stylus tip to X and Y conductors of a digitizer tablet.
Several pen switches, one actuated by pressing the pen tip against a surface and the others actuated by depressing buttons on the pen, change the oscillator frequency to produce frequency changes that represent a pen down condition or "mouse" commands.
A voltage booster circuit including two integrated circuit CMOS inverters and a pair of output capacitors and clamping diodes alternately boost high and low levels of the output of the first inverter and apply them to the power supply terminals of the second CMOS inverter, which then provides a boosted output signal to the conductive stylus