rrpilot
Newbie level 6
Hello Guru's,
I have been trying to wrap my head around some transimpedance amplifier basics and there is some things that trouble me.
Referring to TI's OPA655 op-amp datasheet (**broken link removed**)
The first page shows a bode plot with transimpedance gain. Two things I would like to discuss; transimpedance gain is 120dB when op-amp open loop gain is only 57dB, bandwidth is 1MHz when GBP is only 240MHz.
I have been doing a significant amount of research around these amplifiers and it seems as though the design is done around noise voltage gain on the noninverting terminal. Compensation capacitor in parallel with the feedback resistor is set so that the op-amp is unconditionally stable in terms of the noise voltage not the transimpedance gain.
My Questions:
1) Why does it seem like we can violate GBP formula when operating in transimpedance mode?
2) Why can transimpedance gain (V/A) exceed open loop voltage gain (V/V)?
I am willing to purchase books to help me understand, whatever you guys think will help. I have already been reading "Photodiode Amplifiers - op amp solutions" by Jerald Graeme but I haven't been able to answer these questions from reading in there.
I have been trying to wrap my head around some transimpedance amplifier basics and there is some things that trouble me.
Referring to TI's OPA655 op-amp datasheet (**broken link removed**)
The first page shows a bode plot with transimpedance gain. Two things I would like to discuss; transimpedance gain is 120dB when op-amp open loop gain is only 57dB, bandwidth is 1MHz when GBP is only 240MHz.
I have been doing a significant amount of research around these amplifiers and it seems as though the design is done around noise voltage gain on the noninverting terminal. Compensation capacitor in parallel with the feedback resistor is set so that the op-amp is unconditionally stable in terms of the noise voltage not the transimpedance gain.
My Questions:
1) Why does it seem like we can violate GBP formula when operating in transimpedance mode?
2) Why can transimpedance gain (V/A) exceed open loop voltage gain (V/V)?
I am willing to purchase books to help me understand, whatever you guys think will help. I have already been reading "Photodiode Amplifiers - op amp solutions" by Jerald Graeme but I haven't been able to answer these questions from reading in there.