Re: finding equivalent resistance looking into drain and sou
Analog Cmos design by Razavi has given the method of diong it.Draw the small signal model of MOS ,apply test voltage at drain shorting your input and look for the value of current flowing intio drain.You will find it as ro(resistance due to channel length modulation )and for looking into source it will be 1/gm using the same method.
just apply and input current and then measure the ratio: vds/id,for a particular size of your transistor. In eldo this is a simple script in measures. In cadence you may need to use skill