CMOS down conversion mixer

[chintalaudaykumar]

Hi,
I have designed a folded cascode mixer at 2.4GHz RF and LO is at 2.3GHz,I'm getting 1 dB compression point as 0.56dBm,for calculating IIP3 I have given two tones as 2.401G and 2.4G , while plotting the curves, both the fundamental and third order components are intersecting what could be the problem?I have not designed the matching circuits......will it cause this?

Thanks in advance......

 

[vivek1214]

I think your tone are not correct. I suggest insted of taking 2.401 you should take 2.410GHz. this will give you 100MHz IF and 90MHz for IM, simulate power pattern for this frequency.
hope this will help you.


vivek

 

[tangqin55]

why should change 2.401 to 2.410? if lo frequency is 2.3GHz, RF1=2.4GHz, RF2=2.401GHz. 1st order harmonic is 99MHz, 3rd order harmonic is 101MHz.

Maybe your setting during simulating has problems. how many points did u simulated? were them all completed? you could give us your simu setting.

 

[chintalaudaykumar]

Hii,
I have given my second tone as 2.401G in PAC analysis in spectre.Then IF will be at 101MHz and 3rd order will be at 99MHz.I have sweeped prf from -30 to 10 then both curves are meeting at around 3dBm.The 1st order is linear upto .5dBm and third order is linear till 5dBm prf then it is becoming nonlinear and it is touching 1st order curve at 3dBm in put power...if extrapolate from the linear regions then I'm getting 11 dBm IIP3 what should I do?

Thanks in advance......

 

[tangqin55]

the IIP3 of your mixer is about 11dBm. you could set the start point for extrapolating to -30dBm or -20dBm and then get the IIP3. the 3rd ordr curve would be nonlinear below 10dBm, which doesn't matter. the extrapolate result is what you want.

 

[chintalaudaykumar]

Hii,
What my question is theoritically 1st and 3rd curves should not intersect but in my case they are.Will it be still fine?or is there any wrong with my design?I have taken the extrapolation point as -15dBm.

Thanks in advance......

 

[fanshuo]

During your simulation of IIP3, you should set the two-tone signal level 20dB lower than the 1dB depression point to make sure the transistors still work in "linear" range

 

[chintalaudaykumar]

Hii,
I'm getting 1dB compression point as .5dBm,I have given the 2 tones power as -30dBm,still the 1st and 3rd order are intersecting,but in the case of IIP2 the first and second order are not intersecting.......what can be the problem?

thanks in advance.......

 

[fanshuo]

You mean your highest input level is -30dBm
and what is your input power range?you can nor sweep the input power higher than the -30dBm

 

[guilinwxb]

I have the same problem when i design a mixer which RF=2.44G and LO=2.442G. As I set the RF2=2.4421G when simulate the IIP3 with QPSS+QPAC,the 1st and 3rd order are intersecting every where. But when I set the RF2=2.4401G,the 1st and 3rd order aren't intersecting and do a goodjob.