OPA857: OPA857

user6125065

Part Number: OPA857
Other Parts Discussed in Thread: OPA858, OPA859

We are starting a new design and OPA857 looks great for the dynamic range when lower Tz=5k is used.

In our application, the APD is connected with the cathode to the TIA input and therefore the photocurrent will be sourced by the TIA. Can OPA857 work in this configuration by adjusting the output offset to the lowest possible value, say 0.6V and then obtain a positive going signal? If yes, what are the compromised parameters, if any?

Thank you in advance,

Marcela

over 6 years ago

0 Jacob Freet over 6 years ago

TI__Expert 8700 points

Hi,

Your main challenge would be that the reference voltage is not adjustable for this device, it is permanently fixed at 5/9th the supply voltage. Because the reference is fixed, the output does not have much headroom to swing positively and you wouldn't be able to put much signal in the device.

If you are looking for a more flexible solution you could try the OPA859 or OPA858 op-amps that are completely configurable as transimpedance amplifiers.

Regards,

0 user6125065 over 6 years ago in reply to Jacob Freet

Intellectual 270 points

Hi Jacob,

Thank for the quick answer.

I understand the limitation on the output offset. Is it possible then to bias the input in such a way that the output offset gets to the lowest 0.6V and then the signal goes up from this level?

In fact, is the TIA cable to source photocurrent to the APD, when the cathode is connected to its input?

Meanwhile, I will take a look at the options you have suggested.

Thank you,

Best regards,

Marcela

0 user6125065 over 6 years ago in reply to user6125065

Intellectual 270 points

Hi Jacob,

Please be advised that I need TIA or opamps in die form for integration in opto-receiver hybrid.

Thanks,

Marcela

0 Michael Steffes over 6 years ago in reply to user6125065

Guru 48395 points

Same question from someone else, same project?

There have been some recent decomp introductions that might be interesting for this, the tables in this article list your options,

https://www.planetanalog.com/author.asp?section_id=3404&doc_id=565165&

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OPA857: OPA857