The output level and impedance is why I ended up with the circuit I did. The complementary transconductance output allows a near 5 volt rail to rail swing from a 5 volt supply while driving a 50 ohm transmission line and 50 ohm shunt termination to 5 volts on the driver side.
It would be a power hog though with the output stage drawing about 100mA with a correctly terminated load which is why you would not typically find it on an IC. On Mon, 2 Jan 2012 10:41:01 -0500, Bob Camp <[email protected]> wrote: >Hi > >In most cases it's a T section (two coils, one cap) low pass filter tacked on >to the output of a logic gate (or FPGA output). Net result is a reasonable >sine wave *if* you terminate it correctly. Based on the observations posted on >the list, the filter in the FE-5680 seems to be set up for a 50 ohm resistive >load and is mis-terminated when run into a scope probe. Not to surprisingly, >you get a lot less output voltage into the correct load than into an open >circuit. With a filter, the difference can be significantly more than 2:1. The >logic gate / FPGA is putting out about 3 volts p-p, so that will be the >"filter went away" output level. The matched value will be quite a bit lower >to keep the gate / FPGA from going a bit nuts power wise. > >Bob > > >On Jan 2, 2012, at 9:52 AM, ehydra wrote: > >> Is it possible to sketch the circuit? I can SPICE it. >> >> Symmetry limiting is the holy grail and it is questionable if a discrete >> design is way better than one of the chips. >> >> >> Here is another limiter circuit (by Chris Trask): >> http://ehydra.dyndns.info/NG/LTspice/Negative%20Impedance%20LO%20Driver.pdf >> >> >> - Henry >> >> >> David schrieb: >>> What kind of performance would you expect in this application? Low >>> jitter? 50 ohm output? TTL or better signal levels? Fast rise and >>> fall times? Duty cycle correction? >>> After reading your post I was thinking about how to go about it and >>> ended up with an 8 transistor discrete design using a differential >>> amplifier input and pair of current mirror transconductance amplifiers >>> for the output. I have been looking into designing a pulse generator >>> for oscilloscope calibration and have an interest in GPSDOs so maybe I >>> will prototype this as well just to see what kind of performance a >>> bunch of 2N3904 and 2N4401 jelly bean transistors can provide. >>> On Thu, 29 Dec 2011 21:14:30 -0800, John Beale <[email protected]> >>> wrote: >>>> In case it's useful... there are many ways to get a square wave out from a >>>> sine wave in, but one straightforward way is with a comparator. Some work >>>> better than others. The slow ones won't work at all at 10 MHz, and the >>>> very fast comparators (MAX999, ADCMP600, LT1116 etc.) are more expensive, >>>> and perhaps harder to work with. I tried a MAX9013 in SO-8 package and it >>>> works well for the job. You can see my schematic, circuit and scope plots >>>> at the bottom of this page: >> >> >> -- >> ehydra.dyndns.info >> >> _______________________________________________ >> 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.
