Measurement on the modulation depth of moire and spot size [CRT display]

It is known that moire is the counterpart of readability/focus performance. Nowadays, the requirement on the readability of a CDT is getting higher and forces the gun designers to make the beam spot smaller and smaller. This makes moire inevitable under certain application conditions, because the visibility of the moire pattern is determined by the electron beam spot, while the structure of mask aperture determines moire wavelength. This paper is devoted to the study of the relationship between the visibility of scan moire and spot size from measurements. The modulation depth (MD) of moire and the electron beam spot are measured by a CCD camera. By varying the horizontal Dynamic Astigmatism and Focus (DAF) voltage, the variations of moire MD with beam spot are acquired. It is found that the spot size at both 5% and 50% of luminance distribution can characterize the moire MD in agreement with theoretical calculation.