Originally Posted by LordSte
Interesting topic. I have a similar project in the works (currently on the back-burner). I'm going the digital route, because that way I could easily tag on an HDMI output as well. You never know when TVs will start dropping component inputs too... However, I was unaware that HDMI required licensing. Is there more information about this HDMI licensing? What are the consequences of not licensing? HDMI.org doesn't really go into much of the details for a newcomer like me. I feel that their documentation assumes you're a big company that already knows how to deal with technology licensing.
AFAIK, you can't buy HDMI chip sets on a "hobbiest" level. They are not distributed by the public parts vendors like Digikey, Mouser, etc. Even though you can legally build HDMI products that are not HDCP compatible and do not need licensing keys, I guess they feel the less HDCP capable chips floating around in garage labs, the better. And of course if you want to build a fully HDCP compliant product you must have a licensing agreement anyway to be granted key sets. OTOH, several manufactures now make their own DVI chip sets and since DVI is upward compatible with HDMI, you can just use DVI chips for an HDMI project, just not if HDCP is needed and DVI can also support HDCP.
Those analog demodulator ICs are very interesting. I didn't know they still made stuff like that. Took a look at the NTE821 datasheet
and am totally confused to why there are two chroma inputs and two subcarrier inputs. Glimmie, can you chime in on this?
NTSC chroma is encoded as a DSSC signal. D
arrier. This is a radio technique where the carrier is surpressed and only the sidebands of the signal are transmitted. To reconstruct the full chroma signal prior to demodulation, you must generate an "in phase" and "quadrature phase" subcarrier signal from a local oscillator. That is zero and 90 degrees apart. And of course that oscillator must be locked to the oscillator that modulated the chroma on the transmission side. So to do that there is "burst". Burst is 8-10 cycles of the source subcarrier located on the trailing portion of the sync pulse. This burst is used to sync the oscillator in the receiver's chroma demodulator.
DSSC is still a valid radio transmission practice and can also be implemented digitally. However it's use in NTSC is now legacy and dying fast.
There are many references on line to the theory of NTSC television that dive into this in detail.
FWEIW, PAL, the British standard, is the the same as NTSC except they additionally invert the phase of the chroma sidebands ever other line. This improves stability in the decoding and is why PAL TV sets never had "tint" or hue controls. They didn't need them. Also the subcarrier frequency is different, 4.43mhz vs the 3.58mhz used in NTSC. This is due to the different line and frame rates in PAL. 625lines/50hz vs 525lines/60hz in NTSC.
SECAM, the French color system uses multiple FM carriers and is totally alien to NTSC and PAL. SECAM = S
ontrary to A