Video Amplifier Circuit Doing the Opposite!

should I do any other form of amplification or do you feel this is solid enough to split the signal out 4 ways?

MatCat:
should I do any other form of amplification or do you feel this is solid enough to split the signal out 4 ways?

Depends on the 4 video input channels you are driving. If they have the means to 'turn off' their 75 ohm input matching impedance resistor and have a 'daisy chain' video input and output connectors then you can loop into and out of the first 3 video receivers and only have the last receiver have it's 75 ohm termination resistor turned on. If however you want to drive 4, 75 ohm video input stages in parallel that represents a 18.75 ohm load and your circuit cannot provide enough current to drive them all wired in parallel.

Lefty

Not quite sure what you mean completely... The idea is to take the single video feed and be able to display it on up to 4 separate video devices.

MatCat:
Not quite sure what you mean completely... The idea is to take the single video feed and be able to display it on up to 4 separate video devices.

yes, I realize that, but if the video devices are not designed to operate with a switchable 75 ohm termination resistor (on or off) then your single amp circuit will not be able to drive 4 75 ohm video loads at the same time. Perhaps if you could link to a technical specs of your video devices we could see if they are compatible to 'daisy chain' serial video hookups.

Lefty

Let's assume they do not, because honestly I have no idea what all display devices will be hooked up at the same time. Probably atleast 2 displays, a DVR, and perhaps a set of video goggles.

I don't know how better to state it. That video amp is designed to drive just one 75 ohm video load (receiver).

Lefty

So should I build 4 exact copies of the amp for each output with a single driving input?

MatCat:
So should I build 4 exact copies of the amp for each output with a single driving input?

That might work, but I have no way of knowing that the existing video input signal shown of that schematic can drive four such amp stages. Perhaps there might be commercial amplified video splitter devices available better suited then trying to roll our own?
http://www.cablewholesale.com/specs/composite-splitter/41r4-13500.htm?utm_source=GoogleShopping&utm_medium=organic&zmam=54972865&zmas=1&zmac=1&zmap=41R4-13500&gclid=CJX_l4mw2bICFQpgMgodgn4AxA

Lefty

That defeats my purpose, what are the commercial units doing that I can't do?

MatCat:
That defeats my purpose, what are the commercial units doing that I can't do?

No offence, but I haven't a clue what you can do or not do in the way of video design and construction projects, as I can only judge you on the questions you have asked so far. But I do see a price effective proven commercial solution there that you might want to consider. I buy lots of prebuilt modules and shields that I could probably build myself but looking at it figure I couldn't match the price + time consumed Vs other things I could be designing and building.

Good luck;

Lefty

I shall rephrase my question, what would be the best circuitry to drive all 4 outputs properly? I realize there are time considerations to factor but that isn't a factor for me, thanks.

what would be the best circuitry to drive all 4 outputs properly?

Beauty is in the eyes of the beholder.

Before there was arduino, there is a company called 4d systems that marketed (and still markets) similar stuff (aka shields). One of the more impressive items they marketed is called picaso, a vga signal generator on a shield.

Google it and take a look at its video buffer stages - one of the more elegantly designed buffers in my view.

To me, a proper solution here are four independently buffered outputs, aka picaso.

Take a look at this... I have several hundred of them and I can sample you 3 or 4 with a SASE... No Charge.

Bob

EL4443CS.pdf (339 KB)

Yes but those chips have only one output and several inputs exactly the opposite of what is needed.

A standard video signal is 1V park to peak. That amplifier circuit is a very poor circuit as you can tell from the trace. All those sync pulses should be flat at the same zero volts level. This is because there is no black level clamping in the circuit and the circuit is DC coupled.
You need an AC coupled input and some clamping. Then you need four of them to drive a seprate output each. You can't chain video signals.

Also take a look at Maxim's web site. They have a variety of video amplifiers and buffers, many of which operate off a single supply (no negative voltage supply required).

-j

Do you know any part #'s off the top of your head that would be ideal?

Do you know any part #'s off the top of your head that would be ideal?

Any jfet would be a great video buffer: easy to bias, and good for hundreds of Mhz easily, and natively single rail supply.

Video opamps, until you are very skilled in their applications / layout, are a beast to tame.

MAX4213, EL5050 for you to start with and you will need 1 for every video output. http://www.maximintegrated.com/ have lots of good info about designing what you want to do in the product video section http://www.maximintegrated.com/products/video/ and also try google for video distribution amplifiers (VDA).

Would the LT1193 work well?