With so few information, the only possible hint is to simplify your circuit ... check your frequencies, maybe you can skip the RF divider using PWLs ...

Thank you very much for your reply, Sheldon and Stefan.

What are the clock and input frequencies?
-- The clock is around 100MHz, input frequencies is at the same level.

What are the divide ratios?
-- Four.

Are you using the freqdivide option?
-- Yes, I did.
How many tones/fundamental are you using?
-- Two tone at the RF input (100.5MHz and 100.6MHz), and one tone at LO (400MHz, after dividing should be 100MHz).

Do all the tones at the same frequency have the same fundname
-- No same freq.

or do you have different fundnames for I,Q,I_, and Q_?
-- ? I do not catch this question, sorry.

Thanks,
Tuc

Thank you, Pancho. Here's the related netlist:

PORT_lo (net063 0) port r=50 num=1 type=sine freq=flo_div dbm=plo_div \
       fundname="flo_div"
PORT_rf (vin 0) port r=50 type=sine freq=frf dbm=prf freq2=fund2 dbm2=prf \
       pacdbm=prf mag=1 fundname="frf" fundname2="fund2"

simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \
   tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \
   digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" \
   checklimitdest=psf
dcOp dc write="spectre.dc" maxiters=150 maxsteps=10000 annotate=status
dcOpInfo info what=oppoint where=rawfile
sweepqpss  sweep  param=prf  start=-60  stop=-20  lin=1
+          values=[-40]  {
 qpss  qpss  flexbalance=yes  oversample=[4  1  1]
+       funds=["flo_div"  "frf"  "fund2"]  maxharms=[4  3  3]
+       errpreset=moderate  tstab=100n  annotate=status  freqdivide=4

}

The Spectre version is 6.1.0.151 -- 26 May 2006.

-- Tuc