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.
http://www.prc68.com/I/Diodes.html
Diodes that store charge have different names and that's related to how they are characterized. So PIN, Varactor, SRD
and Noise are all diodes that store charge, and can all be used in any of those application if you have good
characterization data. In the HP 5100 Frequency Synthesizer they use a heater on the SRD in order to increase it's
lifetime so that the 3 MHz drive will generate the needed harmonics. http://www.prc68.com/I/HP5100.shtml These
assemblies are no longer available and getting an SRD with a lifetime long enough to work with a 3 MHz input is a common
as chicken teeth. A solution is to get a large stud mounted Varactor and these do have long lifetimes.
Note a "Comb Generator" is an SRD with an input matching circuit (typically 100 MHz) specified in the frequency domain,
but can also be thought of as a fast pulse generator. I designed and built a hermetically sealed cylindrical module
that was 1 100 MHz input comb generator at Aertech. http://www.prc68.com/I/Aertech.shtml#Comb
<http://www.prc68.com/I/Aertech.shtml#Comb>
The HP 8406 is a lower frequency bench top instrument.
http://www.prc68.com/I/HP8406.shtml
PS Talking about impedance with a non linear device like a diode can lead to
unexpected results.
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.
-------- Original Message --------
Agilent app note AN1054
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