how gunn diode work
Thank you for your answer in advance.
Our lab has several Gunn diodes and they are all 10-year-old.
Recently, I tried to build X-band oscillator in rectangular waveguide.
There is nothing on power spectrum analyzer.
And I found something difference with the data sheet.
From data sheet
Vth=4V, Ith=450mA, Vop=10V, and Iop=370mA.
My measurement
V=1V --> I=340mA
V=2V --> I=850mA
V=3V --> exceed the max. current output level of our power supply.
I also use multimeter to measure the "forward" and "reverse" impedance.
They are the same and are of 4 ohm.
I only test one oscillator but I ues multimeter to measure all the diode.
Their impedance(forward and reverse) are all the same.
Are these Gunn diode dead?or I made some mistake?
Thank you.
Well, it has been a long time! Gunn diode is not a "diode" in the classic sense of the word. It is a block of doped material. If you put a voltage across it, electrons start to form at one end of the block, and after they build up enough, they travel to the other end of the block. When they arrive at the far end, a pulse of current happens. Then the electrons start the cycle again, collecting at the starting end of the GUNN. That is why certain GUNN diodes work best at certain frequencies, the longer the GUNN length, the lower the oscillation frequency.
I vaguely recall that you have to increase the voltage a little higher than normal to get it to oscillate, and then you can reduce it a little as it starts to oscillate. I would use a current limited power supply, or a series resistor, on the next one you fire up.
I also recall running these things on a hot plate surface (70 degrees C), so they would stay in a stable mode of operating over external temperature.
I have had detailed discussions with device PHD's about how GUNN's operate, and after all the mumbo jumbo about domains, etc., it was clear that no one really understood the mechanism.
Added after 14 minutes:
Some ideas:
http://www.mdtcorp.com/Appnotes.html
I guess you need a big capacitor across the bias line, or they blow up!