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    PROBLEM in design of LNA low-gain mode

    hi,
    can anybody provide suggestion on low-gain mode of LNA?
    normally, how does low-gain mode work for high linearity?
    1) design two configuration, one for high gain, another for low gain, and switch between them
    2) directly use the same configuration with different bias?
    which way is better?

    in (1) condition, for a common soruce LNA, will the switch degrade the linearity?

    many thanks!

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  2. #2
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    PROBLEM in design of LNA low-gain mode

    i think the low gain mode , is mode where the bias current is reduced and so the gain ,

    i think for space on chip , they design a single configuation and control its ggain

    khouly



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  3. #3
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    Re: PROBLEM in design of LNA low-gain mode

    I guess so...
    but sometimes I find it is hard to lower the gain enough because, even if half the current, the wide W input mos will still provide gain of several dB.
    I have designed a lna with input mos in linear region when low-gain.
    I don't know whether it is feasible. the gain varies with the vds :(



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  4. #4
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    Re: PROBLEM in design of LNA low-gain mode

    Some RF transceiver manufacturers name Low Gain mode when they bypass the LNA using a switch (this is Low Gain of the receiver).
    In this mode the IP3 of the receiver is higher than High Gain mode (when the LNA is active).

    This is a common topology in WCDMA where the receiver needs to meet high dynamic ranges compare to other systems.

    Using a dynamic bias for an LNA is a challenge meeting the IP3 requirements.



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