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Transistor that works at 20 GHz

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Anton89

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Hello,
could you tell me a transistor model that works at 20 GHz? I need a ADS transistor model to design an low noise amplifier.
I used a avago transistor, but it is conditionally stable (K < 1) and it is hard for me to design.
Could you tell me a transistor with K > 1?
Thanks for helping
 

Depending on how good is the transistor you are working with, maybe you can afford to make it unconditionally stable by adding some parallel/series resistance at the output. Don't do it at the input because your Noise Figure will be way more degraded and you don't want that for an LNA. You will degrade the MAG and the NF a bit but maybe it still performs good for your requirements.
 

megaknaller said:
Depending on how good is the transistor you are working with, maybe you can afford to make it unconditionally stable by adding some parallel/series resistance at the output. Don't do it at the input because your Noise Figure will be way more degraded and you don't want that for an LNA. You will degrade the MAG and the NF a bit but maybe it still performs good for your requirements.
Click to expand...

Hello,
thanks for answering :-D
I'm using the Avago's VMMK-1225 transistor. It is a very good transistor.
This transistor has a high gain at low frequency. With a 10 Ohm series resistor added at output, the transistor is got stable (K > 1) at my work frequency (18.2 GHz). But, it is unstable at 4 GHz when I added real polarization inductor (to drain and to gate).
Now, I wanna ask for you: how can I polarize the transistor to get low the gain at low frequency, so I can get the stability?
Sorry for bad english (I am not english). I hope you understood me
Thanks
 

The source of instability comes most probably from the inductor at the base. Why do you need an inductor at the base? In case you use it for biasing try to do it with some resistive network to avoid it. The resistance of the biasing should be at least 15-20 times your transistor input resistance in order to not load the transistor and avoid noise performance degradation. At the output you still can try to use your inductor and see if it is unconditionally stable over the whole frequency range.
 

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