OPA857-DIE: Transimpedance amplifier

Francesco Raffaelli

Part Number: OPA857-DIE
Other Parts Discussed in Thread: OPA857, , OPA855, LMH32401, OPA858, OPA859, OPA856

Hello,

I was wondering if there are any experimental/test data about this device?

I would expect the input capacitance to be affected by the packaging of the OPA857, therefore I would expect a lower capacity and broader bandwidth for the OPA857-DIE compared to the OPA857.

And also as a consequence, if it's been tested with lower photodiode capacitance than 1.5pF. This is because the photodiodes I intend to use will have a capacitance of 0.3pF.

Kind regards,

Francesco

over 2 years ago

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Francesco,

but you would still need a protection cover over the bond wires, increasing the stray capacitance again. So there's probably no gain when using the OPA857-DIE instead of OPA857.

Referring the detector capacitance, why not running the

OPA857 TINA-TI Reference Design (Rev. A)

Kai

0 Francesco Raffaelli over 2 years ago in reply to kai klaas69

Intellectual 320 points

Hi Kai,

Thanks for the suggestion. If that's the case, it won't help my application. The OPA855 in this case is still the better option.

Kind regards,

Francesco

0 Sean Cashin over 2 years ago in reply to Francesco Raffaelli

TI__Genius 14136 points

Hi Francesco,

The main benefit of using the die is that it allows for lower inductance between IN- and the input capacitance, which can help with overall stability. There is not public testing data for the die package at this time, but here is a reference document that may be helpful. https://www.ti.com/lit/an/sboa337/sboa337.pdf

Please consider the LMH32401 as an alternative. It uses a current input with internal feedback to maximize bandwidth for small capacitance photo-diode inputs.

Best regards,

Sean

0 Francesco Raffaelli over 2 years ago in reply to Sean Cashin

Intellectual 320 points

Hi Sean,

Thank you for your reply.

I had a look at your link as well as at the specs of the LMH32401. In my current application I am indeed using the OPA855, which gives me the best performance: decent noise level as well as a good bandwidth when combined with my high-bandwidth photodiodes. With the OPA855 I easily get a 1.5 GHz 3dB bandwidth, that could be stretched a bit further by playing with the gain etc.

Are you aware of any solution that could bring me to around 5-8 GHz, with similar noise performance of the OPA855 ( which I guess it can be estimated to be approximately -30dBm of optical sensitivity)? I know it is ambitious, but worth asking.

Many Thanks,

Francesco

0 Sean Cashin over 2 years ago in reply to Francesco Raffaelli

TI__Genius 14136 points

Hi Francesco, I have seen customers use a source follower/common drain to buffer the input to the OPA855, since this decreases the effective input current noise. I cannot confirm whether this gives better overall performance than the OPA858, which has a FET input already.

For a small input capacitance, you may be able to extract a little more bandwidth by using the unity gain stable versions of each device (OPA856 and OPA859). Otherwise, these are the highest bandwidth devices available.

Best regards,

Sean

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OPA857-DIE: Transimpedance amplifier