ideally u can consider it infinity ....but actually it will differ e.g. 100dB also it will vary with the frequency (op amp frequency response) ... the GBW will define the point at which the ideal gain drrops to 0 dB
so u need both values basically to start ur design besides the Rout,Rin,slewrate, Iin ...and so on
Razavi CMOS analog desig shall be a very good reference to start up with if u want to learn more
good luck
- - - Updated - - -
ideally u can consider it infinity ....but actually it will differ e.g. 100dB also it will vary with the frequency (op amp frequency response) ... the GBW will define the point at which the ideal gain drrops to 0 dB
so u need both values basically to start ur design besides the Rout,Rin,slewrate, Iin ...and so on
Razavi CMOS analog desig shall be a very good reference to start up with if u want to learn more
good luck