loop gain of two stage of opamp

For conventional two stage opamp
First stage is standard active current mirror as load, diff pair and tail current source
Second stage common source amplifier

Now for the stability analysis, I need to draw the bode's plot were X axis is logarithmic frequency and Y axis is MOD of loop gain [A(s)f(s)], where A(s) is open loop gain and f(s) is feedback factor.

I am not seeing any feedback from output to input, hence f(s) is zero or loop gain is zero.

My question statement is: if there is no visible output to input connection, how can I draw the bode's plot and arrive on the conclusion that there are two poles before unity gain frequency and one needs to connect miller capacitance between first stage to second stage to make it single pole before unity gain frequency.[/img]

The loop gain is not zero. A good reference can be found from P.Gray textbook.
The input-to-output connection is implicit on your opamp system (especially transistor level).
The two poles are usually located at (1) at the connection between the output of 1st stage and input of 2nd stage, (2) at the output of 2nd stage due to large capacitive load at the output. So 2-stage opamp is a 2-pole system.

The concept of loop gain comes when there is a feedback from output to input. Also stability is an issue for only systems with feedback. Any system without feedback like feedforward systems need not bother about stability. (at very high frequencies, all the gate drain parasitics act as feedback and you need to consider them)

When an opamp is built, it is assumed that a feedback loop will be used around it (unless used as a comparator). If the specific feedback factor is not known, it is designed for the worst case feedback factor of 1, i.e unity gain feedback.

Stability analysis needs to be done on the open loop amplifier, considering all the effects of the closed loop, i.e, the loop needs to be broken at some point and the loading conditions must not change when the loop is broken.

The two poles present in your amplifier will make the system go close to instability not because they are present but because when connected in feedback will create a situation where in the closed loop gain can go to infinity(when |Af|=1,phase=180deg). It is feedback which is causing instability.

In your case, do a bode plot analsyis on A(s), You will see the gain dropping according to the presence of the two poles. You have to ensure that the unity gain bandwidth is between the first and second poles, which ensures at least 45 deg phase margin.
Check out without using miller caps. You will see that the two poles occur before the unity gain frequency. Miller caps will split the two poles.

you can simulate the open loop frequence response of your amplifier, you can get the bode plot also get the unity gain freqency. At the unity gain freqency, you can the phase magin and then you can decide whether a miller cap is needed or not.