Noise of folded cascode amp.

[rvenigal]

noise in folded cascode

HI guys,
I was just wondering about the noise of the folded cascode amp.And i have following query(question).
1)Why the noise of bottom transistor in cascode is nondominant contributor towards the overall noise.
2) How to go about reducing the oveall noise of amp.
3) What is the contribution of the tail current noise (may be the flicker) towards the overall nosie of the system.

-rama

 

[Vamsi Mocherla]

noise folded cascode

Dear Rama,

I actually think that the reason is that the amount of current carried actually by the cascode transistor is actually lesser than the main transistors. Hence the transconductance is actually lesser. Remember that the thermal noise is actually proportional to gm(input pair)*[gm(transitor)/gm(input pair) +1].

Hence the best way is to increase the gm of the input pairs.

I really do not think that there will be any major contribution of the tail current source.