I need help in selecting an opamp for transimpedance amplifier. I need a very low current noise density in the order of fA/sqrtHz.Single supply is prefered with a bandwidth greater than 12KHz and gain of 10^6.I have already seen AD8627.
Thanks in advance
If you have a look at the parametric opamp chooser on my website at http://www.sevensoftltd.com/OpAmp.aspx you can filter on current noise density in the "noise I" column. Choosing <= 2fA leaves 483 devices, so you've got plenty of scope for more filtering. The TLC2652 comes to the top of the pile.
If you enter <= 0 in the "Vin CM-" column you will filter to leave devices that work with the inputs at the negative supply, which is probably what you need for single supply operation.
I don't know why you are bothered by gain as it doesn't make much difference in a transimpedance configuration (and I don't list it). A GBW of 12kHz minimum seems terribly low, and you may have stability problems caused by input capacitance. What value feedback resistor do you intend to use?
PS I disagree with Harry, I don't think the ADA4610-2 is a good choice.