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Low noise transistor s2p parameters vs cascade vs cascode

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Full Member level 3
Jan 24, 2018
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Wouldn't a true LNA have at least 2-stages to increase the gain before being modulated in a superheterodyne receiver? I am trying to design on ADS a low noise amplifier but with 2 more stages. First of all, wouldn't you also put a 2nd stage transistor to increase the gain in an LNA, or how would you do it? maybe you would just look for a single transistor that can give you enough gain with a very low noise? I have seen LNA cascode designs before also. Anyway my main point is If I put two common emitters/drain of the same transistors in cascade using s2p file (lets say I configured my gummel_poon model to replicate the s2p file at the specific frequency instead and used this). Would this work correctly if created a 2nd stage in cascade? also would the gummel poon model work correctly if put in cascode, since one is common base/gate, and the other is common emitter/drain would those two configurations throw off the s2p parameters and wouldn't be accurate? or would it be accurate?
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Most of the LNAs for superheterodyne receivers don't need 2 stages. An LNA needs to have low noise (NF < 1dB) and gain greater than 10dB, but not greater than about 15dB, because possible intermods in the first mixer.
May need to do a system analysis to see where you stay with system gain, system linearity, and system noise figure.
If use a BJT for the LNA, a single stage in CE configuration will do the job.
Cascode configuration does not improve the NF because NF id depended only Optimum Noise Impedance that is presented to the first transistor. Therefore a single stage, lowest noise LNA with a reasonable Power Gain will be sufficient.

Note : Cascode configuration is used where a wider bandwidth and improved isolation are needed.
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