elimination Oscillations in LNA ?

Hello all,

please, could someone help me how can we eleiminate the oscillation before or after the operating frequency ?

the tranisitor at that frequency is uncondionnaly stable...

many thx in advance,

<N

The reason of instabilities is primarily, internal feedback of the transistor, external feedback around the transistor caused by external circuit, or excess gain at frequencies outside of the band of operation. Do a sweep of the K-factor over wide band frequencies to ensure unconditional stability outside of the band of operation

To fix instabilities try to:
- use output resistive loading , but this will affect the gain and the IP3.
- use resistor-inductor-capacitor (RLC) feedback to lower the gain at the low frequencies, in this way improving the stability.
- use a filter match at the output of the transistor to decrease the gain at specific frequency (generally for high frequencies).
- use small value inductor source/emitter degeneration.

Thank you Vfone,

Since the Rollet factor and delta satisfy the oscillation condition why i have to add feedback cicuit ?

you don't have...is one of the options

pls, could you see the details in the other theme (Post08 Jul 2009 13:54 How can we eiminate oscillation in the amplifier ?) about my oscillation problem and in

the shift of the frequency..

no reply !