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Simulators >> RF Simulators >> IP2 simulation
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Message started by Lorrenzo2 on Oct 22^nd, 2010, 11:09am

Title: IP2 simulation
Post by Lorrenzo2 on Oct 22^nd, 2010, 11:09am

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?

Title: Re: IP2 simulation
Post by vp1953 on Oct 23^rd, 2010, 8:32am

Hi Lorrenzo,

Why your IF falls much outside the filter BW? Agree totally with Pancho's comments.

Title: Re: IP2 simulation
Post by Lorrenzo2 on Oct 24^th, 2010, 2:29am

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...

Title: Re: IP2 simulation
Post by vp1953 on Oct 24^th, 2010, 10:40am

Hi Lorrenzo,

I think it is better to measure the IM2 component at 5MHz (or other frquency) rather than 1Mhz since 1MHz is also the frequency of an IM3 component.

Well if you are worried about IM2 being much smaller than fundamental for within the filter bandwidth, then would not the same hold true for outside of the filter bandwidth (assuming most of it is coming from stages other than the filter and the filter is just assumed to have an attenuating characteristic outside of the bandwidth)?

If your IM2 is that low, why does it need to be compensated in the first place?

Title: Re: IP2 simulation
Post by vp1953 on Oct 24^th, 2010, 5:48pm

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%