accuracy spice problem

Hey,

It's incredible a good software give so bad result: I inevitably use a wrong way! How should I do?

It's so easy: I simulate a Vdc source (10V) in series with a sin curve Vsin with an amplitude of 1uV (at 10 kHz) and that's all!

If we observe tension voltage we found a sin curve with a 10V offset. But the sin curve is incredibly twisty! It's a square signal!!!!!!!

I try to move a lot of parameters like   RELTOL, ABSTOL, VNTOL, maximum step size… It's impossible to refind the signal who look like a sinus curve. And if we push our VDC voltage to 100V my sinus disepare totaly...

To all spice user: make some test, i can't believe that spice don't allow to simulate that kind of things, where as some software like Psim do that very well...

PS: for information, the scope of application is the study of noise in non linear circuit, so I need to inject noise (µV) in some VDC of 10V. I precise, if we turn down the VDC voltage to 0V, the sinus curve is correct!And more we increase the VDC voltage, more the distortion is important!!! 

Please help me