LNA nf

Discussion in 'Wireless & RF Design' started by kameliya, Jul 24, 2011.

  1. kameliya

    Thread Starter New Member

    Jan 23, 2011
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    I have designed an front-end for zigbee applications at 2.4ghz already i had used on chip inductor(rf spiral sym) at the gate of my cs-inductor degenerated cascode lna and my nf was 2.5db but later i replaced it by the off-chip(from analoglib) one and i put the serries resistance and parallel capacitance of this inductor but my nf drops to .9db and by both of increasing and decreasing the inductor the nf increases i think this shouldn't be occured.i don't know what this happens?
    i'm working by cadence rf-spectre.
    have any body any idea about it?

    thanks in advance.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Are you saying that the NF shouldn't have changed with the addition of the inductor parasitics?
     
  3. kameliya

    Thread Starter New Member

    Jan 23, 2011
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    no I said that the nf improve(becomes better) by replacing the on-chip inductor by the off-chip one and putting the parasitic res and caps??!but it has to becomes worse.I mean i see the vice versa result.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Yes I understand your dilemma. What do you know about the "on chip" inductor model?
     
  5. kameliya

    Thread Starter New Member

    Jan 23, 2011
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    I know the on-chip inductor model completely.I understand what you mean.of course I have found my answer I think the off-chip inductor because of it's high q improves the NF. but not up to this level(from 2.5db to .9db)but maybe it is possible.I'm not sure.
     
    Last edited: Aug 7, 2011
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