LNA's S21 is not occuring at the desired frequency ???

[bcdeepak]

hi

i am making a dual band LNA for 2.4GHz and 1.8GHz . i am using switches (NMOS) to tune the LNA between the two frequencies.

my problem is ..... when i tune the LNA to 1.8GHz , the input and output impedances are becoming real at 1.8GHz and matching is also fine but still the maximum gain(S21) is occuring at 2.2GHz but not at 1.8GHz. Actually the max gain should also occur at 1.8GHz


why is it happening so ??????? what should i do ?

 

[khouly]

can u post the schematic ?

khouly

 

[bcdeepak]

hi khouly,

i observed that if i go for wide range of freq, this problem is occuring, so i reduced the required freq range, so now i sorted out the problem

thanks for ur reply

 

[bcdeepak]

i think some capacitance is playing role in the shift

 

[khouly]

maybe the parasitics due to layout , try to reduce them

khouly