I want to make a simple numerically-controlled attenuator for a 6Vtt signal with a bandwidth of 20MHz. Looking at analog switches I was wondering if I could simply use a classic 4066 for this task. Philips state an on-state frequency response of 90MHz for their HEF4066B but they don't show any graphs. Would this work? They sure are cheap compared to other switches.
I used to do that with the FET quad array SD5400 but that seems to have fallen from grace by now.
Check out the THS73xx series, mainly the THS7313. Has a 2:1 input mux. Guess you don't need three channels but for a little over a buck, why not?
I don't know if the mux can be switched fast enough via I2C to do it in one V-sync period. The 7313 supports the 400kbps mode. Supposedly works in I2C high speed (3.4Mbps) but AFAIK that's not guaranteed.
When it has to be blazingly fast you can do the diode quad and toroid. The first time I did that was for my final project back at the university. I needed three samplers to hit the sweet spots on a CCD readout register. The sampling window had to be 15nsec and you couldn't be off more than a couple nsec in timing, and absolutely no jitter. IIRC I used 74AS logic as a drive, plus "analog slope enhancers". The toroids were, of course, hand wound. Didn't want to wait for a Mini Circuits order and wanted to stay within budget. The folks at that institute were a bit baffled when I asked for the budget the project would have. Guess nobody ever did that before. Got into trouble anyway because I spent half that budget on phone calls and telex charges (remember those?) just to find all the parts I needed. But, I stayed about a hundred under the grand total.
Don't know of a way to do it with one IC. But you know about the several nice miniDIP sync-detector chips. The ones I've used are spot on for timing. You could drive a flipflop with the sync to get a select signal. I'd buffer the video first to lower the signal impedance, and use a 74hc4053 to make the signal selection, with a G=2 follower amp after, plus a 75R resistor for the video out. You may need to have capacitive coupling and black-level restoration in the mix, but this can be done with the unused 4053 sections, using a set of timing pulses derived from the sync chip. I don't recall the exact details just now, but my old design drawings are in a folder.
Pericom has some good multiplexers for video switching - e.g. P15V331Q.
They also look useful for other things than video as they have have fast turn-on/turn-off times and good capacitance to ground parameters, most other fast multiplexers have horrendous capacitance to ground - presumably because they use large devices to get the on-resistance low. I was recently looking for something along the lines of the HC4053 but with fast switching times and this was the closest I could find - it does only a limited input voltage range though as it is intended for video.
It is available from Digikey although their search engine often cannot find it!!! (PI5V331Q-ND)
I find the classic 4016/4066 is inconvenient to use because it does not have level shifters on the logic control lines although for video it would be OK because of the limited voltage excursion of video (0-1V).
There are a variety of switch-amplifier combinations, as others have said, but I like the hc4053 with a roll-your-own amplifier. It's hard to find a faster, lower-capacitance switch, certainly not a cheaper, easier-to-get one! It fills the bill for video.
Almost anything would do, as long as it is glitch free after the syncs, a couple of anything from maxim's stable would be OK, as long as the diff gain/phase specs are ok Switching video in analogue is dying out Personally I'm glad to see the end of PAL/NTSC based equipment, a pain in the arse in post production, great for transmission though, well thought out, by the time they got PAL working
Yes. A lot of tasty digital kit is now available for the high quality studio end. I must mention, that at the pleb end, i.e. the burgeoning UK video security industry. It still relies near totally on analogue composite PAL. Indeed, it's difficult to buy a (good!) security cam that offers digital out. Stick a PAL cam on a pole, send the 6MHz balanced/unbalanced off for monitoring and the car park riff-raff are still clearly identifiable. Digitise and compress it a little and you're left with a nice pretty picture but near useless for the intended purpose. (I'm biased. I earn money from designing analogue matrix routers :). john