Black Burst Generator


Posted on Feb 5, 2014

CMOS analog multiplexers were frequently used at the ETC for various purposes. Here I thought I would present a circuit I borrowed from a Dave Jones design, and slightly modified it, to build a black burst generator. Video systems need sync to ensure that all the devices are in time with each other, and sync is also a component of composite video.


Black Burst Generator
Click here to download the full size of the above Circuit.

In the less recent past sync signals included composite sync, subcarrier, blanking, and burst flag. In addition some devices, usually cameras, required horizontal and vertical drives. That`s six signals, all in time, created by a sync generator and distributed with distribution amplifiers. All are low true pulses except subcarrier, which is a 3. 58 MHz sinewave. Subcarrier is used to encode color content, it is present in the image component as chroma, and as a color reference in the burst. Don`t confuse black burst with burst. Black burst is a fully encoded video signal with black for image content, burst is the 9 cycles of subcarrier that appears between the breezeway and the back porch of all composite video signals. As the first four sync signals mentioned above are used to create a composite video signal, a composite video signal has encoded within it the same four signals. Composite sync is manifest directly in composite video, subcarrier is present in the burst, burst flag determines when the burst happens, and blanking will determine the precise location of the beginning of the front porch and the end of the back porch. As chips proliferated that were able to decode this information from a composite video signal, black burst, nothing more than a black video signal, became a ubiquitous simpler way of distributing sync information. Using black burst, a single wire can carry all the sync information a device needs. My...




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