Cell parameter extraction method for AC plasma display panels

Abstract

This paper presents a cell parameter extraction method for three-electrode AC plasma display panels (PDPs). This method uses three different two-electrode AC discharges to extract the cell capacitances. The drive point capacitances of the cell with and without a two-electrode dark discharge were measured, and the cell capacitances were extracted from them. The extracted cell capacitances agree well with those obtained from a three-dimensional electromagnetic simulation. Electrical equivalent circuits of the plasma were constructed using Jung's model [Y.K. Jung, J.W. Seo, Y.H. Kim, B.K. Kang, Circuit model for two-electrode AC discharge, IEEE Trans. Plasma Sci., 31(3), pp. 362–368, 2003.] and the measured firing voltages. A circuit model for the cell was constructed using the cell capacitances and the equivalent circuits for the plasma. The results of electrical simulation using this circuit model agree well with the measurements, indicating that the presented circuit model would be useful for simulating the electrical behaviors of a three-electrode AC PDP.

Introduction

The typical cell structure of an AC plasma display panel (AC PDP) is shown in Fig. 1. It has three electrodes: the data (X), scan (Y), and common (Z) electrodes. The X electrode is located on the rear glass plate, and the Y and Z electrodes are located on the front glass plate. All electrodes are covered with either a dielectric/MgO or a dielectric/phosphor layer. The dielectric rib separates the front and rear glass plates and provides a discharge space. The Y and Z electrodes are orthogonal to the X electrode and form a matrix pattern; however, in Fig. 1(b), the front glass plate was rotated 90° from the actual direction to represent the cell structure easily. When there is no discharge in the discharge gap, the cell can be represented by a circuit consisting of nine capacitors, as shown in Fig. 1(b). The following notations have been adopted to represent different cell capacitances; the subscripts d, g, and w before the underline represent the dielectric rib or glass, the discharge gap, and the wall dielectric over electrodes, respectively; and the subscripts x, y, and z after the underline represent the corresponding electrodes. When there is a discharge between a pair of electrodes, the plasma shunts the corresponding gap capacitor, as represented by the current sources in Fig. 1(b). The number n represents the number of facing discharges in the cell. It is two if the cell has discharges between the X and both the Y and Z electrodes. Otherwise, it is one. Direct measurements of these capacitances and plasma properties are impossible because all electrodes are separated from the discharge gap by dielectrics.

Most AC PDPs are driven by a very complicated waveform to display a picture properly. For an electrical engineer designing a new drive circuit for an AC PDP, it would be very convenient to have an electrical equivalent circuit since numerous accurate circuit simulation tools would be available to estimate the consequences of changes on the drive waveform and cell structure on the picture quality. A few circuit models have been reported for the electrical simulation of AC PDPs [1], [2], [3]. Furutani et al. modeled a cell of a three-electrode AC PDP with 22 capacitors and 12 discharge paths [1]. The plasma on each discharge path was represented with a simple discharge model, and an electrical–physical hybrid simulation was used to calculate responses of the cell for various input waveforms. This method is quite accurate, but not applicable to general circuit simulation tools. Tamita et al. modeled the cell with circuit elements, which are available in most circuit simulation tools [2]. They modeled the plasma with a variable resistor, and the time-dependent change of resistance was modeled with a first-order differential equation. The differential equation requires several physical constants, such as the growth and decay time constants for discharge, number of initial electrons, conductivity of adjacent cells, rate of change of conductivity, etc. Because of this, this model has limited application for the cell driven by a very complicated waveform. Jung et al. described an electrical equivalent circuit for a two-electrode AC discharge [3]. This model consisted of a series connection of an equivalent circuit for the plasma and two capacitors for the insulators. The equivalent circuit for the plasma was constructed using the measured electrical properties of a two-electrode discharge and standard circuit elements; thus it can be implemented easily on most circuit simulation tools. This circuit for the plasma could be used as a building block for constructing an electrical equivalent circuit for the three-electrode AC PDP.

All of these circuits require accurate values of cell capacitances for simulation. This paper presents a method of measuring the cell parameters of a three-electrode AC PDP. Because all electrodes of the AC PDP are separated from the discharge gap by dielectrics, the cell parameters were measured indirectly using the properties of an AC discharge between a pair of electrodes. The structure of the experimental three-electrode AC PDP is given in Section 2. A circuit model for cell capacitance extraction is described in Section 3. An electrical equivalent circuit of the experimental device and the results of electrical simulation are given in Section 4. A conclusion is given in Section 5.