Re: More fun with avalanche pulsers
Thanks. For now I'm trying to achieve the fastest possible risetime and a not-too-ugly flat top. I have somewhat achieved that already.... I can reduce the overshoot and ringing by adjusting the trimmer cap. I have a calculated 380 ps 10-90% risetime now. What might a few ohms in series with the charge line do to that? (The 2N2369 did give a cleaner output as in the earlier photos, but only about 650 ps risetime).
I left the neatly-cut end of the .141 line open. If I wanted to continue over-stuffing this Minibox I could solder an SMA connector to it and add another piece of line. But I also don't want to overtax the BFR505 which is pulsed every 2 us. At slower rep rates (relaxation osc mode), other experimenters were seeing failures in a few hours with longer pulses than 16 ns...
I remember your previous advice on matching and dynamic impedance changes. By trial and error I found that paralleling another 100 ohm emitter resistor (i.e. 33 ohm emitter load) improved everything except output amplitude, of which there is still plenty (6-7 volts). All these traces are: SMA output, SMA-GR adapter, GR 10x attenuator, 3' of GR 50 ohm cable into the 50 ohm sampling head. So any mismatches in the cable or sampler should also be attentuated on reflection.
When removing the cable and plugging the attenuator directly into the head, the persistence of the ringing through the whole flat top is now visible without the cable attenuation... As expected, the risetime improved also (but naturally the overshoot is worse). 320 ps displayed (310 corrected) without the cable. 380/370 with it.