http://www.its.caltech.edu/~hajimiri/pdf/non-linear.transmission.pdf The above indicates how cascaded NLTLs using CMOS processes can be used to construct NLTLs that sharpen both edges of a pulse. 2.5ps fwhm impulses can also be produced. Bruce
On Tuesday, April 12, 2016 04:42:06 PM jimlux 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. _______________________________________________ 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.