hello!
 thanks for reading my post. I'm trying to simulate the IIP2 of a fully differential transconductor + mixer core + transimpedance amplifier(TIA). The TIA is composed of a differential Opamp with two feedback resistance (Rf=1Kohm) in parallel with two feedback capacitor (Cf=32pF).It's also used to be a 1st low pass filter (BW=5MHz). The LO frequncy is 2.399GHz.  

I set up imbalanced feedback resistance with 1kohm and 0.9ohm and two tone test with 1MHz tone separation (Frf1=2.579GHz & Frf2=2.58GHz) to simulate IP2 of mixer by PSS, so the 2nd order harmonic frequency will be 1MHz baseband. Besides, in order to plot the IIP2 figure (Pin v.s Pout) of intercept point, I set another tone (Frf3=2.401) to be downconverted to 2MHz (Frf3-Flo=2.401G-2.399G=2M) as a 1st order harmonic. But the result that I get looks like something wrong. Do I set up correctly for IIP2 simulation?

i want to design the Current-Driven Passive Mixer with IP2 Calibration for Zero IF Integrated Receivers, and the output of mixer is also connected to the ADC.
if the two-tone(2.401&2.402G) are downconverted by LO(2.399G) inside the bandwidth of filter(5MHz), their fundamental tone (2M &3M) which is lager much than IM2(1MHz) will saturate ADC, so I think if I only want to detect IM2 by ADC, the fundamental tone which is downconverted must be outside of the bandwidth.


correct me if I am wrong please..

thank you...

Hi Lorrenzo,

On further thinking I think i see your point, though it looks like a very complicated setup

- does your mixer have nearly same conversion gain at frf1 and frf3?
- what about DC content at the output & dynamic range of the TIA (the output is not saturated or something like that?)
- when you say something looks wrong, can you post a picture of this
- also instead of a 10% difference in the resistor values, can you try a smaller difference of say 1%