i am designing a TIA for the photodiode and using LTC6078 opamp . However i need a very large gain 100Meg Ohm and gain bandwidth product of LTC 6078 is 750kHz. So the theoretical bandwidth of the circuit (calculated from GBW product) is 750 000 / 100 000 000 = 0.0075 Hz... I think i have done something wrong in the calculation or interpreted the gain of TIA incorrectly.
Could anyone suggest where I have gone wrong?