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Explanation why interstage inductor is placed between 2 transistors

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Advanced Member level 4
Mar 7, 2005
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hi all,

I've seen some Cascoded LNA design where interstage inductor were placed between 2 transistors. I do not get the clear idea about it !! I am looking for a theoretical explanations for this. Can anyone help......this is really urgent!!

Please, any site or books or journals to get a clear idea ?


interstage matching inductor

This involves what is called "interstage peaking" It goes back to about 1940. There is series peaking and shunt peaking. It forms a filter like structure with the parasitic capacitances of the active devices. You trade off a one pole gentle rolloff response for a flatter one with sharp rolloff.

tube cascode amplifier

Hi Professional,

Although I'm a laity in IC design as I'm specilized in GSM RF system, but I'm still
wandering this "pole" in the discussion above can be applied for RF application band ? I heard that LNA is a wideband device comapred to IF programmable amplifier in wireless communication Receive, So
1. How to deside this pole location in frequency in wireless comm.?
2. What's the advantage if works for gentle rolloff way in above discussion, would
it be applicable to wireless comm. system for instance, GSM, BT...

Thanks !!

interstage match

The only reason of the interstage match in a cascode LNA is to increase the gain. But from my experience the LNA become very unstable.
In a vacuum tube cascode amplifier this would help because the gain is lower compared with actual solid-state transistors.

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