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pankaj
Joined: 06 Jun 2001
Posts: 68
Helped: 1
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 02 Feb 2003 12:30 Detection of Chroma |
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Hello,
I have to design a circuit which detects the presence of Y and C on a S-Video Connection.
Detection of Y signal is easy since it contains the sync information and it can be passed through a sync detector and the presence of video can be detected.
But what could be the simplest way of detecting the C signal
Pankaj
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MonkeyBusiness
Joined: 16 Jan 2003
Posts: 42
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| 02 Feb 2003 17:17 |
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| A simple approach would be to use a filter matched for the C signal bandwidth, and detect signal energy after the filter. You can use a squaring or an ABS value for this purpose, or even a simple diode detector, depending on the available S/N.
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TurboPC
Joined: 14 Mar 2002
Posts: 148
Helped: 1
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| 05 Feb 2003 5:23 |
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What do you want to compare the C signal to? Something compared to nothing? Or chroma compared to Y?
A chroma signal contains generally only frequencies in the range of the subcarrier frequency: 3.58 MHz in NTSC or 4.43 MHz in PAL.
If it is only signal presence, you could probably integrate the color signal using a diode and a "capacitor with a resistor in parallel" and control the time constant. Then use a comparator to detect the presence.
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pankaj
Joined: 06 Jun 2001
Posts: 68
Helped: 1
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| 09 Feb 2003 10:27 |
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Yes, I just want to detect the presence of the signal and not compare it to anything.
pankaj
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cbsirio
Joined: 05 Jan 2003
Posts: 69
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| 10 Feb 2003 23:37 |
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try to make an amplifier that fed the signal to an LC filter centered on 4.43 MHz , then rectify it and use a comparator on the rectified signal.
HTH, Sirio.
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Tavarnelle
Joined: 25 Jan 2003
Posts: 8
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| 13 Feb 2003 15:04 |
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I use a TBA 395 to detect the presence of color on a circuit.
It is the simplest way:the circuit open a port in "burst" position and control
the presence of a 4.43 signal.It is possible to make the same circuit
with TLL or other similar system(eg a PIC).It is very important to control only the pedestal of syncro,because if you try to find 4.43 signal in the time of image you have the possibility to detect also 4.43 signal in luminance part.
Alberto
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TurboPC
Joined: 14 Mar 2002
Posts: 148
Helped: 1
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| 14 Feb 2003 1:28 |
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| Tavarnelle wrote: |
I use a TBA 395 to detect the presence of color on a circuit.
It is the simplest way:the circuit open a port in "burst" position and control
the presence of a 4.43 signal.It is possible to make the same circuit
with TLL or other similar system(eg a PIC).It is very important to control only the pedestal of syncro,because if you try to find 4.43 signal in the time of image you have the possibility to detect also 4.43 signal in luminance part.
Alberto |
Good point. He could also pass the luma signal into a sync extractor like the GS1881 or LM1881 and use the "back porch" output pin to trig the detection on the color burst signal at 4.43MHz (or 3.58 in NTSC) from the chroma signal.
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Tavarnelle
Joined: 25 Jan 2003
Posts: 8
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| 14 Feb 2003 11:40 |
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Exactly:I made a similar circuit with
LM1881.
It gone perfectly.
Alberto.
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