Video measurements pose a tough challenge because of the complexity of video waveforms. Such waveforms often combine the signals that represent the video picture with the timing information that is needed to display the picture. Although some video measurements demand specialized instruments, others can be easily made with a general-purpose oscilloscope. In the 20- page application note, "Introduction to Video Measurements Using a 4000 Series Digital Phosphor Oscilloscope," Tektronix, Inc. (www.tektronix. com) examines critical video-measurement issues and how they relate to the capabilities of different types of oscilloscopes.
The note begins by delving into basic video standards and formats ranging from NTSC, PAL, and SECAM to newer systems like high-definition television (HDTV). It then looks at how those signals are processed, which leads to a discussion of composite, component, and Y/C video as well as HDTV formats. Once this transmission is complete, the processed image is accurately reproduced. This task requires that the camera and video display be synchronized.
The bulk of the note is devoted to the measurement of video signals. Digital phosphor oscilloscopes (DPOs) offer the traditional benefits of a digital storage oscilloscope (DSO) ranging from data storage to sophisticated triggers. Like analog oscilloscopes, they also capture and display waveform information in three dimensions: amplitude, time, and distribution of amplitude over time. The note provides some specification guidelines as well. To ensure accurate representation of the signal, for example, a good rule of thumb is to use an oscilloscope with an analog bandwidth that is at least five times the signal's bandwidth.
For many video engineers, the most critical display issue is the need for an intensity-graded display. Subtle signal variations can reveal a video system that works versus one that does not. To analyze video waveforms, one also must have a stable display. The last section of this application note provides an overview of common video-signal measurements, such as amplitude, timing, and video-frequency response. Clearly, this document was created to explain the needs of today's video engineers and illustrate how the 4000 series DPO can satisfy those demands. With many illustrative graphics and a plethora of information on video signals and how to measure them, however, this paper serves as a good primer - or refresher - for any engineer working in this arena.
Tektronix, Inc., 14200 SW Karl Braun Dr., P.O. Box 500, Beaverton, OR 97077; (800) 835-9433