# stability factor "K" of an LNA .........

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#### bcdeepak

##### Member level 5
i designed an inductively degenerated common source LNA
as my s22 is veryless i some what added a resistor of 15ohm at the output , so now s22 is improved to 10.9db

i resimulated the ckt with that 15 ohm and noted the s-parameters.

the calculated stability factor K(from S-parameters) is 69 , i know that if k>1 the ckt is stable

but here my K is too much greater than 1 , is this value of K acceptable ?? or is there any wrong in the ckt ??

deepak.

#### khouly

yeah it is ok , but is S22 10.9 dB or -10.9 dB

and also did u check the LNA NF after this resistor or not

khouly

#### bcdeepak

##### Member level 5

sorry, my S22 is -10.9db not +10.9db

yeah, again i calculated the NF , NF is 1.2db

one more doubt , S21 is 7.8db , is it fine??

what r the typical value of s21??

#### khouly

the noise figure is very good , but the gain should be known from the LNA spec's , but i have seen many LNAs have S21 from 16 to 12 dB maybe 10

khouly

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