Thank for the quick reply.
You're right! add VCVS can isolate each stage. I will try that.
But as you said, load noise will be isolated as well.
In almost ideal unilateral case, this is not an issue. But not so accurate otherwise.
That promote me another related question:
Can we turn the noise of part of the circuit off?
I know most modern device models have such feature by specifying "isnoisy=no". However, what if i want to turn off the noise of a group of devices (e.g. in a subckt). Do you have any suggestions?
In Eldo, it is supported! I guess spectre has the similar feature, isn't it?
I hope this could help more people than myself. :-)
Thanks a lot