Q:

Bridge rectifier simulation problem

I use virtuoso cadence to make two bridge rectifier,one of them use NMOS to replace the diode,and the other use DION_MM directly,like the picture shown

But their simulation are wrong,like the picture below shown,and i want to ask where is my schematic wrong?the gnd position?The red line is the wave of right schematic,and the blue line is the left,and the black line is the alternating current voltage source 

A:

But their simulation are wrong,like the picture below shown,and i want
  to ask where is my schematic wrong?the gnd position?

You need to place your circuit simulator's ground reference point on the bottom of the load resistor if you want to display the bridge rectified output as is normally presented.
Any sim will calculate the voltage at a node relative to the ground reference point and because you have yours on the AC output, you will not see the voltage directly across the load resistor.
If you want to simultaneously show the AC voltage pattern AND the bridge output then you need to use a "voltage controlled voltage source" conncted to one of the input voltages you want to display then, on the output of the VCVS, tie it to the ground reference point. Think of it like a differential amplifier but in-built into most sims: -

Red = input voltage relative to ground
Blue = output voltage relative to ground
Green = voltage across R1 re-referenced to ground so it can be viewed correctly

