Hi
Does this PGA is for a single slope ADC ?
In order to answer we need  understand the probelm, this is the cool thing in Analog  ;)
Explain how you plan to use it and I will answer you
Good luck
Erez

Hi Erez and Jerry,
Thanks for your reply.

Yesterday, I thought of the following as the flow of design of OPAMP. Tell me if I go wrong anywhere.

The Preamp output goes to 13 Bit ADC...(which defines us the no. of time constants for settling which is=ln(2^N)=(~10) for N=13 and the gain error which is= 1/(AF) <1/[2^(N+1]=(~0.01%)), where A=Open-loop Gain of OPAMP and F is feedback factor.

The ADC's sampling time-window would tell us the settling time specification for the OPAMP, which is = (Time constant of the closed-loop OPAMP*no.of time constants). The Preamp's closed loop gain is defined by resistive feedback... (0 to 45dB insteps of 1.5dB).

From the resistive feedback we know what is feedback factor (F).

Find open-loop gain A from gain error in-equality 1/(AF) <1/[2^(N+1] --------(1)

Time constant of closed-loop OPAMP= (sampling time/ no. of time constants)

From sampling time and  no. of time constants we can find the Time constant of the closed-loop OPAMP.

Time constant of closed-loop OPAMP= 1/{(1+A*F)*[W-3dB]} ---------- (2)

where W-3dB is -3dB angular frequency of the open-loop OPAMP

Substitute A found from (1) & F,  in (2) to find W-3dB for the open-loop OPAMP.

Hence its UGB=(A*W-3dB) can be found.

As Jerry said Input & output signal swing would tell us how much is Slewing time & Linearity requirement.

Thanks,
Packiaraj.V.