0.13um 1.2v LNA low gain design ?

Dear All :

I design a LNA FM band. But the P1dB is -10dBm , It is high. If I want to do Low gain in LNA ? Any comment, Or any experience for this, When the current is about 1mA . Thanks

P1dB -10dBm is high? Maybe you want to say is low.
Low gain for LNA you can have turning OFF the LNA Vcc. The insertion loss through the LNA with Vcc OFF it will give you the low gain mode.
Beware that some RF system designs do not require big delta between high gain and low gain mode. A good number for this delta is approximately 25d

Dear vfone :

Thanks your comment, I know the low gain -10dBm using capactive divider, it can easy to finish it. But in the high gain model , Is the P1dB is the same, Because I don't have sense about it. I know in the high gain mode the P1dB can low. But How low is it ? -20dBm ? or Others , thanks

I am not very sure about your concern.
If you ask if the P1dB is the same in high gain mode (LNA ON) and in low gain mode (LNA OFF), I can say that P1dB with LNA OFF is higher because there is no nonlinear device active.

Dear vfone :
Thanks your comment. In general RF system , the P1dB is different with LNA high /low gain mode, How do we to partition it ? Like when input is -100dBm , LNA is in high gain mode , -10dBm , the LNA is in low gain mode. What is boundary ? In your experiement ? How large P1dB is good ? Thanks

You have to do a RF System Analysis to find the compression point of the receiver with LNA ON or OFF. The requirements depends by the highest input level requirements and by the level of external blockers.

Probably the first mixer have the highest contribution in this test.

When the LNA is ON, first of all you get compression from the P1dB of the LNA, and second, because in this case the gain before the first mixer is high, the system it will accept a lower signal at antenna connector until will compress the first mixer.

When the LNA is OFF you don?t get compression from the LNA, and the gain before the mixer is low, and the system will accept higher input level at antenna connector before compression of the first mixer.

Dear vfone :

Another questions. If the LNA can single / differential input . In the single mode . it is like a active balun in IC. How do finish it ? And if the active balun is in LNA , how to finish the low/ high gain in this case ? If the Low gain is using capacitance divider , Thanks