1) it depends on the required quality of the video
2) yes, resolution will greatly determine the amount of data that must be processed
3) datasheet info as a first step
4) distortion, or it may refuse to work at all
Do a search of "video op amp" just as you would for "audio op amp." The AD811 is just the handiest I had, but there are many others.
2) yes, resolution will greatly determine the amount of data that must be processed
3) datasheet info as a first step
4) distortion, or it may refuse to work at all
Do a search of "video op amp" just as you would for "audio op amp." The AD811 is just the handiest I had, but there are many others.
If the video is in the analogue domain then you are looking at wide bandwidth. For example the broadcast TV UK standard would have been DC to 6Mhz. VHS quality video took that down to around 3Mhz. With decreasing bandwidth comes loss of HF definition.
So the minimum specs also depend on the bandwidth you expect to see. The term "video" covers a huge spectrum.
So the minimum specs also depend on the bandwidth you expect to see. The term "video" covers a huge spectrum.
Probably not. The lowly 741 may be capable of some type of (very poor quality) video. Generally, video requires a fast op amp with wide bandwidth. Along with compatibility with the 75-ohm standard as mentioned, and probably some other characteristics other more knowledgeable members know of. Which all relates to your 3rd question; I think the video format and quality determines the amount of information that must be processed per time period, then an op amp must be found that can keep up with that.
Yes, and add eg 720i, 1080i, color vs black & white, etc. There is a lot of information in a video waveform, and it can't all be placed in a narrow bandwidth. That is true of audio, also. If you just want to playback speech, 300-3kHz is adequate; for music there's a ~tenfold difference either side, because there's a lot more information there. Bandwidth here is referring to the op amp's response to a wide range of frequencies. For quality video it's tens of megahertz.
Look at the numbers down the side of gratings on this test card. Oversimplifying somewhat, these are the "frequency" that corresponds to that level of detail. The 5.25Mhz are very fine vertical lines.
Think of audio. If you cut off the audio at 4Khz things would start to sound dull. Cut off the high video frequencies and the fine detail starts to disappear.
Those figures for the Amiga are the resolution. The PAL (phase alternate line) means the signal conforms to the broadcast standard and can be applied to a TV to display, either directly as composite video or via a UHF modulator to enable the signal to be received via an aerial input.
You still need the high bandwidth even if the video is low resolution because the TV signal is made up of various synchronisation pulses that have to be passed with no distortion. I would guess you still need a couple of meg bandwidth even for an ancient computer video signal.
Think of audio. If you cut off the audio at 4Khz things would start to sound dull. Cut off the high video frequencies and the fine detail starts to disappear.
Those figures for the Amiga are the resolution. The PAL (phase alternate line) means the signal conforms to the broadcast standard and can be applied to a TV to display, either directly as composite video or via a UHF modulator to enable the signal to be received via an aerial input.
You still need the high bandwidth even if the video is low resolution because the TV signal is made up of various synchronisation pulses that have to be passed with no distortion. I would guess you still need a couple of meg bandwidth even for an ancient computer video signal.
Attachments
I've ordered two of these:
http://www.datasheetcatalog.org/datasheet/lineartechnology/lt1253.pdf
I had tried the circuit with a TL074, because it was there, and the results were rather poor...
http://www.datasheetcatalog.org/datasheet/lineartechnology/lt1253.pdf
I had tried the circuit with a TL074, because it was there, and the results were rather poor...
Differential gain is the video analog of audio IM distortion. AFAIK there is no audio equivalent to differential phase.
Sofaspud mentioned the Analog Devices AD811 which I've used LOTS of for HD video. They are outstanding for this task but you need to know how to deal with CFB amps. They're not difficult but you don't go changing gain by altering the feedback resistor as it also changes the bandwidth.
Your audio amps won't do well - they'll do some but it's up to you how much bandwidth you can live without.
High speed amps do better on 4 layer boards with a ground plane so they don't turn into oscillators.
For video you don't want high impedance systems as they get unstable and noisy. Low impedance will run a little higher power but that's a small price for good performance.
G²
RGB to ypbpr...
the Amiga has a 15Khz sync signal which I'm yet to find a tv that can sync it on the VGA input... however, they appear to be able to sync it on the ypbpr input...
Why don't you use a part that is made for this application? take a look at the MAXIM site for example: Amplifiers - Maxim
But there are many manufacturers that offer these kind of amps..
But there are many manufacturers that offer these kind of amps..
If you're looking at the LT chip consider the AD8024. It's not 'better' but the data sheet offers more guidance.
With Voltage feedback opamps you will not require input buffers as the gain of the amps can be set with the feedback resistors. With CFB amps you'll want unity gain input buffers so you can change gains via input resistors of stage 2.
Question: Is your RGB with / without sync? Sync on Green? Separate sync? More difficult yet, separate H and V sync.
G²
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composite sync, but it's 15Khz...
which I'm yet to find a TV or monitor that can accept this on the VGA input... SCART should, but very few TVs here in Australia have SCART anymore, however, I've found every TV in the house to happily sync the 15Khz fed directly in to the ypbpr input, it's just a matter of getting the colours right
It's not working right at all, I have no green?
I found the "Colour Wheel" thing in workbench... which confused me, as I was fairly sure there was meant to be some green in there?
This is with the LT1254CN Opamp:
http://www.datasheetcatalog.org/datasheet/lineartechnology/lt1253.pdf
Pinout on page 2!
So I plugged my LCD monitor back in, which has a GBS8200 built in to the base... ah yes, green... so my circuit is displaying green as red, blue, black, and purple! as well as combining multiple shades of every other colour into one colour!
So, I then plugged the TL074CN opamp in to the circuit, which lacks the bandwidth required to display a proper image, data sheet found here, I believe the pinouts are THE same, and I've checked it four times now!
http://ampslab.com/PDF/tl074cn.pdf
and was greeted by this:
yes, it does display black as bright green... but at least it displays green?!?!
Faults LT1254? I've tried two different ICs, and they give identical results....
I think I'll order/find some different opamps, and see what happens... but can anyone explain whats going on?!?
I found the "Colour Wheel" thing in workbench... which confused me, as I was fairly sure there was meant to be some green in there?
This is with the LT1254CN Opamp:
http://www.datasheetcatalog.org/datasheet/lineartechnology/lt1253.pdf
Pinout on page 2!
So I plugged my LCD monitor back in, which has a GBS8200 built in to the base... ah yes, green... so my circuit is displaying green as red, blue, black, and purple! as well as combining multiple shades of every other colour into one colour!
So, I then plugged the TL074CN opamp in to the circuit, which lacks the bandwidth required to display a proper image, data sheet found here, I believe the pinouts are THE same, and I've checked it four times now!
http://ampslab.com/PDF/tl074cn.pdf
and was greeted by this:
yes, it does display black as bright green... but at least it displays green?!?!
Faults LT1254? I've tried two different ICs, and they give identical results....
I think I'll order/find some different opamps, and see what happens... but can anyone explain whats going on?!?
That pretty much answered the issue...
The EL2045 opamps originally used in this circuit are VOLTAGE FEEDBACK... while the TL1253 (and even the LMH6722 suggested earlier on) are CURRENT FEEDBACK!
they're completely different! and it explains why the TL074 gives correct colours, as it's also voltage feedback...
sorry, I haven't posted the schematic, it was a design by someone else, on the Amiga forum
Amiga RGB to YPrPb convertor - English Amiga Board
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