[time-nuts] Fast risetime pulse generator

paul swed paulswedb at gmail.com
Fri Apr 15 20:41:44 UTC 2016


Bill
Now this discussion gets really interesting. You are doing something and
will report results. You have my attention.
Regards
Paul
WB8TSL

On Fri, Apr 15, 2016 at 12:27 PM, BIll Ezell <wje at quackers.net> wrote:

> I'm amazed at how much traffic this has generated.
> Thanks Brooke, you're exactly on-topic as usual.
>
> As I said originally, I wanted a quick-and-dirty-and-cheap, and I'm using
> an SMMD-835 SRD. Making up the test layout tonight.
> I'm starting with a 100 uA bias on the diode, and a 20 pF diode-to-load
> coupling cap, driving the SRD with a 5V 1Mhz square-wave.
>
> I'm also going to try the 2N3904 Vce-reverse-bias avalanche idea just for
> fun.
>
> I'll post again after I have some results.
>
> PS - as I've mentioned before, I trim these things. I hate the
> endlessly-requoted replies, impossible to parse what's actually been said.
>
> --- Brooke post, trimmed --
> Hi:
>
> The idea with a step recovery diode is that during forward bias the diode
> stores charge.  When the polarity reverses the diode continues to conduct
> until the charge has been depleted.  At that time the diode stops
> conducting and opens.
> Suppose this was done using a square wave. The length of the positive
> (charging) half of waveform needs to be long enough so that the diode if
> fully charged (a function of the diode lifetime and charging current).
> Then on the negative half (discharging) when all the charge has been
> extracted the diode turns of making a sharp edge.  So the diode lifetime is
> important in relation to input drive frequency.  For a sinewave drive the
> lifetime should be about 1/4 the period at the recommended drive level.
>
> --
> Bill Ezell
> ----------
> The day Microsoft makes something that doesn't suck
> will be the day they make vacuum cleaners.
> Or maybe Windows 10.
>
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