Hi to all,
   If u go through simple two stage opamp design,in that case can see that gm6 = 10*gm6 (approximately):where
gm1 = trnscounductance of one of the i/p pair trnsistors &
gm6 = trnscounductance of 2nd stg i/p trnsistor.
   My doubte is if we want 60 deg PM,why we are selecting only 10 as a multipying factor why not other one?
In Holberg,he has given explanation for cc > 0.22 * (cload).Buut npthing for transconductance related anything.
   Please,can anybody guide me in this regards?
   Thnx.

avlsi yes we can get everything through experience but you have to search for the scientific meaning too.

the answer to the question is:

the 2 stage opamp has a right hand side zero which can cause for us stability problem, so to overcome it you have either to bring it to the left hand side using a compensation resistance with the miller capacitance or to keep it in the right hand but move it far away from the W0db (i.e. 10*W0db)

as the Z (zero) = gm6/Cc   , and the W0db=gm2/Cc = GainBW product (approx.)

so gm6 should be 10 times larger than gm2.

GBW= Gain * BW = Gain*P1 = (A1*A2) * (1/A2*Cc*R1)   where A1 is the gain of the first stage = gm1*R1 and R1 is the output resistance of the first stage.

so the result will be = gm1*R1*A2 / A2*Cc*R1 = gm1/Cc = gm2/Cc  where 1,2 are the input symetrical differential transistors.

aamar