Hi Two very conventional RF chokes (couple of uH each) and an NPO cap (couple hundred pf) are all you really need for the square to sine filter. It's probably a good idea to put a blocking cap on the thing as well. If you want to get fancy, put a three resistor 6 db pad on it as well. That way your cable will be rationally terminated over a fairly wide bandwidth.
Bob On Sep 27, 2013, at 2:23 PM, Tom Minnis <[email protected]> wrote: > I haven't even begun to look for video amps yet. I may not need one if I > filter an output of an high powered 5V buffer. What I hear is a simple > passive low pass filter will do. That being the case, I may put them on all > the outputs and make it a jumper option. The other project brewing here is > developing a precision time stamp transceiver which needs the fast edges as > opposed to the synthesizer reference which needs the accurate frequency > aspect. Thanks again for all your helpful ideas. > Tom > > On 9/27/2013 3:53 AM, Charles Steinmetz wrote: >> Tom wrote: >> >>> One of my first applications is to use a 10MHz output to phaselock a VCXO >>> master clock in a radio transceiver. * * * Next I went to IDT to >>> find the best logic buffer I could find. I am looking at the IDT >>> 74FCT38072 2 channel clock driver for PPS. It can drive about 50mA if >>> needed with 1nS rise and fall times. The one I am looking at for 10MHz is >>> the ICS553 4 channel clock driver. This one is good for 25mA drive and >>> they actually give a typical output impedance spec of 20 Ohms. With a 3.3V >>> supply, it has 1nS rise and fall times and a little faster with a 5V >>> supply, 0.7nS and 35mA drive. To make a sine wave should I use one of the >>> 4 ports on the 4 port driver to input to the filter or should I try to hook >>> the filter input directly to the clock driver input? >>> Are there tried and true 10MHz filter circuits or is that a non issue? >>> After the filter would come the video amp set up for a 50 Ohm drive and >>> into a splitter. That sound simple enough. >> >> I strongly agree with Magnus that distributing square waves is asking for >> trouble and that converting to sine is preferable unless there is some very >> good reason not to. >> >> IIRC, you said the source is CMOS. So you can do all of your fanout >> digitally, then filter each output (I believe that is what Bob had in mind). >> Or, as you appear to be contemplating based on your comments above, you >> could convert to sine immediately and then do the fanout in the analog >> domain with a video DA or whatever. One reasonable filter type to hang on a >> CMOS output is an L-C-L "tee" filter (there is really no reason not to add >> one more shunt C at the end, for L-C-L-C). This filter needs some >> termination at all times -- the open circuit output voltage can be pretty >> high. But you can usually get away with an internal termination of ~1k or >> so. If you need more current to get the output level you want, parallel >> several CMOS outputs (all on the same hex buffer chip, preferably). There >> is no need for very fast edges, particularly if you are filtering to sine >> wave. Nothing exotic is necessary. >> >> The same is true even if you decide to distribute square waves. The fewer >> higher harmonics you have, the better off you will be. >> >> Best regards, >> >> Charles >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
