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Gunn diodes are usually specified to work within a range of frequencies, e.g ~10GHz. I can easily understand why there is an upper bound for the frequency of operation of a Gunn diode, but I can't figure out why there is a lower bound: after all, what is used is the negative resistance of the diode: what prevent us to use this negative resistance at frequencies as low as 100hz, beside the fact that it would be very stupid to use a Gunn diode at such frequencies?

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Limitations of self resonant choke frequency>10Ghz and high enough L to isolate the DC bias from loading the negative resistance limits the LF cutoff.

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    \$\begingroup\$ Your answer is somewhat cryptic for me. Can you elaborate? \$\endgroup\$ – MikeTeX Sep 25 '16 at 19:53
  • \$\begingroup\$ you have to apply a low impedance DC voltage to bias at -Z threshold that is voltage source is high Z in GHz range with a suitable choke. unfortunately interwinding capacitance or leakage C increases with L which reduces f self resonant frequency so L must be small (nH) and thus fMin is large. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 25 '16 at 19:59
  • \$\begingroup\$ I think I understand. But why is it ideally necessary to apply a high impedance DC voltage to bias the diode ? \$\endgroup\$ – MikeTeX Sep 25 '16 at 20:06
  • \$\begingroup\$ if a voltage source with Low Z is applied to a resonator, it lowers the Q or gain and stops oscillating . Normally Q is the ratio of effective real/reactive for impedance and expressed by f/-3dB BW . This applies to LC resonators with R load as well. for parallel mode. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 25 '16 at 20:12
  • \$\begingroup\$ cheers mike....tony \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Sep 25 '16 at 20:29

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