Bruce J. Penney

Digital-to-Analog Conversion — Data and Filter Requirements

Ringing in the analog waveform caused by the filter response to the converted digital data is not a new problem. Early digital-based character generators for composite television applications caused significant ringing because the digital data produced too sharp an edge in the picture. Due to the specifications of component digital video, these edge effects are once again becoming more apparent in television operations. This paper discusses the results of using 13.5-MHz, luminance sampling to obtain flat analog bandwidth to 5.75 MHz, and how the filter template required by the international standard will inevitably result in some noticeable ringing on fast picture transitions. Data requirements in the digital domain are analyzed using 2-T pulses as an example while suggesting a different edge transition that will produce much less ringing. Designers are advised to consider the application of filters or edge processing to reduce the ringing due to digitally generated signals.