Light pen detection for plasma panels using specially timed scanning

Abstract

An enhanced light pen capability is provided in plasma display panels by applying specially timed write and erase pulses in a scanning manner over the panel, the pulses being shaped and positioned relative to the normal sustain pulse sequence in such manner that a light pulse is emitted upon the resulting momentary write or erase which is detected by a light pen of standard design while avoiding any but transient modification to the state of the cell wall capacitance. The scanned write pulses advantageously assume the form of modified write pulses with shortened duration and less abrupt terminations than is usual. Dynamic keep-alive circuitry for applying location-dependent priming enhances the operating margins to permit reliable, constant-voltage write and erase signals for all cell locations.