Revisiting the analogue video decoder: Brushing up on your comb filters

Daniel Ogilvie, SingMai Electronics
EDN (July 11, 2012)

The basic function of the video decoder is to accept analogue video from a wide variety of sources such as broadcast, DVD players, cameras and video cassette recorders, in either NTSC or PAL format and still occasionally SECAM, separate it into its component parts, luminance and chrominance, and output it in some digital video standard, usually BT656, a multiplexed Y/Cb/Cr video format with embedded timing signals running at a clock rate of 27MHz.

Most major semiconductor companies, for example Texas Instruments, NXP (formerly Philips Semiconductors) and Analog Devices, and a large number of smaller companies manufacture an analogue video decoder. In addition many companies have integrated this function into SoC (System on Chip) integrated circuits.

With such a large number of video decoders in the market it might seem an unnecessary indulgence to spend time looking again at the design of this fundamental but apparently obsolete building block, and certainly new designs are not appearing on the market and haven't done so for three or four years.

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