Oops, sorry I didn't realize you needed 150 ps rise time. Rob Sent from my iPad
> On Apr 12, 2016, at 6:02 PM, "jimlux" <jim...@earthlink.net> wrote: > > > >> On 4/12/16 1:30 PM, BIll Ezell wrote: >> (cross-posted to volt-nuts) >> After paying only limited attention to this topic, I suddenly have a >> need for a pulse generator that has <150 ps risetime and a pulse width >> of at least 2 ns. 100mv amplitude or more is fine. I've looked at the >> classic Jim Williams avalanche generator, but I don't want to have to >> deal with the (relatively) high voltage source needed. >> >> I've done microwave design using Gunn diodes, so I'm drawn to using a >> step-recovery diode. The topology seems very straightforward, and I can >> build it right onto a BNC connector, no PCB. >> >> I'm thinking using an SMD835 diode, biased at ~1ma. The (sketchy) >> datasheet claims a T of 20 nsecs and a Tr of 85 ps, Cj of 0.4 to 0.8 pf. >> > > how about a fast digital buffer? > I don't think Potatochip semi is quite in the 150ps range (although you could > look at their website and see). > > But we use microwave dividers and such all the time at 8 GHz. Check places > like Hittite. > > > > >> Questions: >> >> The obvious, is it reasonable? >> >> Is the bias current reasonable? I'm assuming the bias current is >> actually dependent on the repetition rate, you need enough current to >> replenish the charge within one pulse cycle. I suppose I could compute >> it from the stated junction capacitance, but I'm not sure that's the >> only factor. >> >> Will the stored charge actually give me the desired transition rate into >> 50 ohms? Hmm, again I should be able to compute this, but any other >> factors ignoring the non-diode ones like cap inductance? >> >> How should I compute the coupling cap from the diode to the load? Use >> the impedance at the pulse rep rate? Seems reasonable. BTW, I don't care >> about droop in the pulse, just the risetime. (measuring overshoot in >> an HF amp). Again, just want to verify that the obvious answer is the >> correct one. I clearly need to be very careful about the inductance. >> >> Thanks, Bill >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > -- > If this email is spam, report it to > https://support.onlymyemail.com/view/report_spam/ODExMjI6MTg3MTg2MDE0ODpyb2JAbmMwYi5jb206ZGVsaXZlcmVk > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.