We are interested in using an OPA855 as a TIA with a Hamamatsu S5973 photodiode. The junction capacitance is 1.6 pF. The desired bandwidth is 1 GHz and as much gain as can be achieved with that bandwidth. Do you have a recommendation for the feedback resistor value? Also, will the OPA855 drive a 50 ohm load? If not, do you have a recommendation for a wideband buffer amplifier?
Thank you,
David
Hi David,
for a desired bandwidth of 1GHz the feedback resistance can only be as small as 1k:
And a phase lead feedback capacitance of 230fF would be necessary to allow a stable performance with a phase margin of 50°:
Kai
Hello David and Kai,
Thank you Kai for the simulations! It is tricky to achieve 1GHz of overall system bandwidth. Looks like around 1kOhm gain will be around the max the application would achieve at the first stage with minimal peaking as Kai has just shown. The OPA855 has a relatively large output current drive of around 80mA, and can drive 50 ohm load up to its output voltage range. Also, here is a TIA calculator we have available to quickly check these requirements at a maximally flat bandwidth with a Q factor of 0.7 and phase margin of 65 degrees.
Thank you,
Sima
