Keywords: Radiolocation, handwriting digitizing, graphics tablet, CRT-pen, digital whiteboard, 3-D joystick, machine control, and virtual reality.

Abstract: Two or more receivers of known location receive RF bursts from a wireless moving object containing a transmitter that transmits periodic RF bursts. The receivers are gated with precision swept timing that repeats at the exact transmit RF burst period to produce precision expanded time representations of the received RF bursts. The expanded time representations correspond to RF burst arrival times from the transmitter, which are used to calculate the location of the transmitter. A writing pen application includes an RF transmitter in a writing pen and four RF receivers beneath the surface of a writing tablet where RF propagation from the pen to the receivers cannot be blocked by a user's hand. Two RF transmitters, one located at each end of the pen, may be employed to measure pen tilt and for 3-D tracking. Spatial resolution is more than 600 dpi at 100 location fixes per second.

Applications include handwriting digitizing tablets, graphic tablets, signature pads, CRT-based selection and editing pen, digital whiteboards, 3-D joysticks, PDA input device, machine control, digital surgery, and virtual reality systems.