How to get Low IF spectrum of mixer in Spectre ?

I use spectre RF for simulation.

When I simulate a mixer, the IF is set at 100kHz. So I put 900.1MHz for RF input and 900MHz for LO. But the IF is so low that everytime the simulation took a lot of time and then idled without completion. I tried changing some parameters in simulation to make it converge faster, but nothing works. If there someone who can tell me how to solve the problem ? Thx

The simulator will be PSS and it will take 10us simulation time. Minimum beat frequency is 100kHz and this resolution will complicate the simulation but never mind if the circuit is not very complex.
Add some "initialization"time to heat-up the mixer and try convergence adds to get a result.
In fact there are many things to obtain a robust result and PSS is always tedious task..

Otherwise, you may also try QPSS in IC5.0