[SOLVED] How down-conversion mixer IIP3 influnce the receiver linearity?

[fenglingke]

Dear all,
I work for a RF receiver system design now. I need define RF down-conversion mixer parameter and circuit that mixer following LNA. One of RF mixer circuit performance is Gain=3dB ,IIP3=9dBm OIP3=12dBm; another circuits RF mixer performance is Gain=10dB ,IIP3=2dBm OIP3=12dBm.From reduce the receiver NF, i could choose the second RF down-conversion mixer circuit?
I know 1/OIP3=1/OIP3+G1/OIP2+......, So OIP3 decided the linearity of system,but I confuse with how RF down-conversion mixer IIP3 influnce the linearity of system?
or how define the IIP3 base on receiver performanc?
could someone tell me? thanks

 

[vfone]

You posted the formula for OIP3 (1/OIP3=1/OIP3+G1/OIP2+....)

The formula for IIP3 for a cascaded system is:
IIP3_total = 1 / [(1/IIP3_1)+(G1/IIP3_2)+(G1*G2/IIP3_3)+....]

Take a look to this applet for better understanding of the IIP3 influence of each stage:
CASCADE08.swf

 

[tony_lth]

Use the free software SysCal to simulation, you don't need to calculate yourself.

 

[biff44]

where does one find syscal?

 

[buckaroo]

Usually, the linearity is dominated by mixer and sometimes LNA, because the OOB linearity of the IF circuits is quite good;
For voltage mode LNA, the linearity is always dominated by the Gm stage of mixer; for current mode LNA, the linearity is always dominated by LNA;
You can get the linearity spec from system, then, just use the linearity spec for the dominated block, it is precise enough;

 

[tony_lth]

**broken link removed**
Here you can find a trial version of Syscal.