A REAL TIME CURVE TRACER AND WAVEFORM GENERATOR FOR AC PLASMA DISPLAYS (COMPUTER, ELECTRICAL MEASUREMENT, INTERACTIVE)

The first real time curve tracer for AC plasma display panels is presented. It draws wall charge transfer curves, a variant of the traditional transfer curve that relies on measured wall charge rather than wall voltage. Since the curves are qualitative due to varying cell capacitance, the results presented rely on comparisons between different curves rather than analysis of the shape of isolated curves.;A special programmable instrument, based on a minicomputer with extra hardware, was built to perform experiments and generate curves. The computer generates sustain waveforms to drive the display under test, samples the wall charge data, does error correction, then plots the transfer curves on a graphics display, all at the rate of about 5 curves per second. The user interactively changes voltages and timing associated with a high level graphical representation of the different voltage levels in a sustain waveform. The user can modify curve tracer operation by editing a small, interpretive program of special purpose curve tracer commands. Curve tracer and waveform parameters can be modified as curves are being drawn by manipulating a digital potentiometer.;A number of effects were investigated. The phenomena of plasma sweep-out due to voltage transitions was shown to affect a number of different waveforms. The range of effects from near and far neighboring cells was illustrated. The effect of waveform duty factor on firing voltage was shown. It was found that narrow pulses in front of the falling edge of the sustain pulse can destroy the plasma in such a way as to increase the charge transfer. Two different methods were developed for setting the wall voltage to any desired value. The significance of small amounts of wall charge that remain in an off cell was illustrated.;The most unusual effect discovered was the hysteresis in the charge transfer curve. There is a different charge transfer curve for each sustain voltage, and in particular, there are different curves for cells turning off than for cells turning on. The spread of the curves accounts for the majority of the bistable range. This effect was also shown to exist in DC cells with series capacitors.