OPA855: OPA855 as TIA with photodiode FDS015

Selvedin Hodzic

Part Number: OPA855

Hello together,

My goal is the following: I want to detect fast LED flashes with a photodiode (measure light intensity-Illumination curve is wanted). LED has the wavelength of 620nm. The flash length is in the range 10-250ns. The repetition rate should be in the range of 10Hz, but if it is lower, it is not critical.

I have chosen PIN photodiode FDS015 for this. It has a bandwidth of 1.75GHz. Diode capacity is 0.65pF. I want to use OPA855 with this photodiode as TIA. Now the question is:

Do I realize the OPA855 as a simple TIA with only feedback resistor and feedback capacitor and on the inverting input is my photodiode?

I am connecting the non-inverting input of OPA855 to ground und using supply voltage from -2.5V to +2.5 V (split supply configuration).

Now I am building a PCB of TIA and wanted to leave other places on the PCB free if I need other components. Could you help me there? How should my construction look like?

Kind Regards

Selvedin Hodzic

over 4 years ago

0 Michael Steffes over 4 years ago

Guru 48395 points

Well, your 10nsec min pulse width might suggest a required BW, the higher that bandwidth, the lower the transimpedance gain can be. what Zt stage bandwidth would you like,

0 Selvedin Hodzic over 4 years ago in reply to Michael Steffes

Prodigy 210 points

Hi Michael,

Thanks for a quick response. I think that I did not correctly understand your question regarding Zt stage bandwidth.

I do not have requirements regarding BW.

Regards

Selvedin Hodzic

0 Michael Steffes over 4 years ago in reply to Selvedin Hodzic

Guru 48395 points

yes you do, how clean do you want your 10nsec pulse to be, if we target say a 2nsec rise/fall time that is 175MHz BW. (about).

0 Selvedin Hodzic over 4 years ago in reply to Michael Steffes

Prodigy 210 points

Hi Michael,

Do you think 1750MHz? I wrote that bandwidth of my photodiode is 1.75GHz =1750MHz. Rise/fall time of photodiode is 35ps/0.2ns. The bandwidth of the photodiode is 0.35/0.2ns= 1.75GHz.

Selvedin Hodzic

0 Michael Steffes over 4 years ago in reply to Selvedin Hodzic

Guru 48395 points

Good luck with that.

0 Hasan Babiker31 over 4 years ago in reply to Selvedin Hodzic

TI__Genius 15555 points

Hello Selvedin,

It will be very difficult to achieve that bandwidth with the OPA855 and maintain stability... I've attached a TINA circuit with a TIA of around 1GHz bandwidth & 530-ohm transimpedance gain.

Best,

Hasan Babiker

Selvedin.TSC

0 Selvedin Hodzic over 4 years ago in reply to Hasan Babiker31

Prodigy 210 points

Hello Hasan,

Thank you very much for explanation and this simulation.

Kind Regards

Selvedin Hodzic

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OPA855: OPA855 as TIA with photodiode FDS015