How down-conversion mixer IIP3 influnce the receiver linearity?
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
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
Use the free software SysCal to simulation, you don't need to calculate yourself.
where does one find syscal?
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;
SysCalc6 - RF Design Software by Arden Technologies
Here you can find a trial version of Syscal.