The MARK III Flat Matrix CRT has 16 color dots tiled in a 4 x 4 matrix pattern. The grid-electrodes match this pattern with four vertical (Y) and four horizontal (X) elements that intersect. A line cathode is located at each intersection. The Y grid electrodes run between the cathodes and the anode electrodes, while the X grid electrodes are behind the cathodes and serve as a back plane.
The X and Y grid electrodes are placed at a positive potential with respect to the cathode. The potential around the cathode becomes positive, creating an electric potential gradient that slopes down toward the high voltage anode electrode.
Thermoelectrons emitted by the cathode travel down this gradient and pass through the mesh of the Y grid electrode. They are accelerated by the anode voltage and penetrate the anode electrode, striking the phosphor screen. The excited phosphor emit light.
When either or both of the X and Y grid electrodes are placed at a negative potential with respect to the cathode, the potential around the cathode becomes negative, preventing electron travel toward the anode electrode.
No light is emitted because no electrons reach the phosphor screen.
The diagram above shows the basic control sequence of the driving circuits.
Each X-electrode is driven by the scanning signal at 1/4 duty cycle.
The Y-electrodes are driven by the pixel data signals. The duration of each data signal is varied according to the input video signal level of the corresponding pixel.
When the positive scanning signal and the data signal are both applied to the X and Y electrode, the selected phosphor dots emit light.