And by varying the reverse bias through a current source (or moderately
large fixed resistor) you can make them into nifty phase shifters.

Jim


I wrote: NOT PIN - Diodes - as they wouldn't snap.

i mean Band Switching diodes for TV-Tuners like the BA244 and the BA682.

BA682 Datasheet:

http://www.vishay.com/docs/85530/85530.pdf

- and they snap! Try it!

Jorgen
dj0ud

Hi Jim -

And on what delay timescale it works?

regards -
Henry


"RST Engineering" schrieb im Newsbeitrag
...
And by varying the reverse bias through a current source (or moderately
large fixed resistor) you can make them into nifty phase shifters.

Jim


I wrote: NOT PIN - Diodes - as they wouldn't snap.

i mean Band Switching diodes for TV-Tuners like the BA244 and the
BA682.

BA682 Datasheet:

http://www.vishay.com/docs/85530/85530.pdf

- and they snap! Try it!

Jorgen
dj0ud

A step-recovery ("snap") diode works on the principle of stored charge in
the diode. During the forward biased half of the AC waveform, the diode is
a very low impedance and it stores excess charge; during the reverse biased
half of the waveform, the diode remains a low impedance until the stored
charge is depleted, at which time the diode "snaps" into high impedance.
This snap acts much like a spark-gap transmitter, in that a tremendous
number of higher order harmonics are generated. In general (and there are
ways to enhance this), the power available from any harmonic is around 1/n *
Pin, where n is the order of the harmonic and Pin is the RF power input to
the diode.

Biasing the diode simply varies the point on the reverse cycle of the AC
waveform where the diode snaps. For maximum power, you try to get the diode
to snap at the peak of the waveform. However, by varying the diode bias,
you can get it to snap before or after the peak of the waveform. Generally
you can get it to snap plus or minus about 30 degrees about the peak before
the snap action degrades.

60 degrees of phase shift is nothing to talk about unless you are working
with the 10th harmonic, which means a phase shift of 600 degrees. Now
you've got something to work with.

Jim

Thank you Jim for your longly explanations. I already knew the charge
storage process, but the phasing aspect was new and interesting.
My question about phase delay was in another direction.
To be concrete:
How to delay (=phase shift) a 145MegHz signal (mostly sinus waveform) with a
snap diode? After reading your explanation I cannot see how to achieve a
non-snapping action here. Maybe that would work with the diode if you
modulate it with dc current getting delay in the ps timescale.
Another question would be if it possible with the snap diode to make a power
amp in some form of ringing oscillator. Of course, it should be modulable at
least with FM.

- Henry



"RST Engineering" schrieb im Newsbeitrag
...
A step-recovery ("snap") diode works on the principle of stored charge in
the diode. During the forward biased half of the AC waveform, the diode
is
a very low impedance and it stores excess charge; during the reverse
biased
half of the waveform, the diode remains a low impedance until the stored
charge is depleted, at which time the diode "snaps" into high impedance.
This snap acts much like a spark-gap transmitter, in that a tremendous
number of higher order harmonics are generated. In general (and there are
ways to enhance this), the power available from any harmonic is around 1/n
*
Pin, where n is the order of the harmonic and Pin is the RF power input to
the diode.

Biasing the diode simply varies the point on the reverse cycle of the AC
waveform where the diode snaps. For maximum power, you try to get the
diode
to snap at the peak of the waveform. However, by varying the diode bias,
you can get it to snap before or after the peak of the waveform.
Generally
you can get it to snap plus or minus about 30 degrees about the peak
before
the snap action degrades.

60 degrees of phase shift is nothing to talk about unless you are working
with the 10th harmonic, which means a phase shift of 600 degrees. Now
you've got something to work with.

Jim