Hi,
I don't know all that much about video and buffering it but am always willing, and hoping to learn.
I have two broadcast video feeds that I need to switch between, using an analog switch. Assuming that all the gain and output loading requirements of each feed are already dealt with behind the switch by the previous designer, I think I just need a unity gain buffer on the output side of the switch since the switch itself cannot drive any loads, and needs to be protected from the outside world as well.
I admit that don't know the best way to configure the output buffer. I am picking up an existing design and trying to learn my way through it, as it should be obvious I am not all that learned in such things. I do search web sites and app notes, but its possible that this one is just too simple for them to bother with, or I am not looking in the right place.
I am figuring a EL2244 or equivalent. Does it require a feedback ckt, a resistor between the output and the negative input, or just the output tied back to the inverting input? (not very good at ascii art yet) Since I seek unity gain, is it just a 750 ohm from output to inverting input, and from there another 750 ohm to ground?
I am looking at one schematic where the output of such an analog switch is an LT1361 (righteous bucks for that! ) and it is just video into the +, and a 750 ohm feedback to the - input. Not knowing what is going on back upstream, I can't guess exactly why that value was chosen, and if it is needed, or just a designer's method that works as well as other configurations.
I am doing is reading app notes, and looking at existing designs trying to learn on the fly, and I am not seeing a lot of consistency in what is done, so I gather there are many opinions, and they all work, but since I don't know the designers, I can't ask them what they were thinking, and why they chose what they did.
That leads me to this group, and hopefully its not too inane a question to be asking.
I like to hear about web sites I can learn this from, so pointers would be gratefully accepted as well as opinions on how to configure this buffer.
Thanks for your consideration.
John