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One transistor enables clean HDTV and NTSC Video sync separation

The growing popularity and availability of HDTV creates a small revolution in the television industry. New video systems must be able to handle the composite signal standard NTSC (National Television System Committee), as well as the HD signals. Whereas, in that it relates to low cost and low power drive system designers the simplest solution, this article describes one transistor network which allows a single video sync separator work for HDTV and NTSC systems.
In the NTSC signal sample in Figure 1 are identified by a burst of color and color subcarriers. "The level slice" is drawing in half-way down the drop for horizontal synchronization. Differences in the colour burst or dark blue under the carrier may dive below the surface of the slice is causing false synchronization pulses in addition to the horizontal sync signal 15 kHz. HD (High Definition) signals (Figure 2) the color information is carried out separately, so there is no color bursting or subnosná cause false synchronization pulses. Note, however, that the horizontal synchronization pulse is shorter and higher frequencies (20 kHz).

It is useful in the case of a single synchronization Separator will work with HD and NTSC signals. Whereas that false triggers can occur with NTSC signals, you can add the filter in the synchronization path separator to reduce the height of the color of the discharge and the carrier signals. This filter cannot be included in the detection of HD, because its less synchronization pulse would also dilute the effect, causing the missed event triggers.

ISL59885 is the synchronization separator, which offers HD and NTSC detection. Output, the HD, it is provided, which responds to input type-for NTSC high and low for HD this external pin can be used to insert a low-pass filter to the synchronization path separator to avoid false synchronization pulses in composite video. The circuit is shown in Figure 3. When the signal is detected the composite (NTSC/PAL), the filter is enabled using a logic high at the base of the transistor. When the component is detected a signal (HD), the filter is turned off with the HD pin in the low state logic. Although the transistor is prohibited during the HD, low pass filter to filter out the noise is still present on the entry.

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Posted by yono at 2:17 AM

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