What do you gain when you use an op amp like this...

http://www.ti.com/product/opa380

I always thought a transimpedance amplifier was just a configuration thing. However, this is specifically called an transimpedance amplifier....

What makes this different from any other high bandwidth FET input amplifier?

 

It is built from the ground up to be a current to voltage converter of very small currents. Plus, it has an auto-zero servo.

ak

 

I am using it with this guy

http://www.vishay.com/docs/81521/bpw34.pdf

My circuit is figure 1, but with Vbias to gnd.

Rfeedback is 100 ohms.

What I do not get is why I get a full voltage swing up to 4.5V. According to the spec sheet, the photodiode can not even go up to 1mA. To get 4.5V, I would need over 25mA. Am I missing something?

Edit: my pulses are at 20 Hz.