TLV271: Mistake in Noise Error calculation by hand

manideep kumar

Part Number: TLV271
Other Parts Discussed in Thread: OPA846

Hi,

I'm using TLV271 Op-Amp as a transimpedence amplifier. Connecting a photodiode (current source) to convert current to voltage. There i'm successful.

But my problem is, I made a hand calculation on noise error. I'm getting a peak to peak noise as 18v. This is a MISTAKE. I have attached the calculation excel sheet. Please identify where i have done the mistake.

Noise_Cal.xlsx

over 5 years ago

0 Michael Steffes over 5 years ago

Guru 47485 points

Hello Manideep,

Without looking at your excel sheet, you cannot do a transimpedance noise calculation without the capacitance on the inverting node - even if only the parasitic - here is a good discussion, says high speed, but applies generally,

www.ti.com/.../sboa122.pdf

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Manideep,

here you will find a very detailed examplary calculation:

e2e.ti.com/.../2539745

Kai

0 Michael Steffes over 5 years ago in reply to kai klaas69

Guru 47485 points

Yes, that SBOA060 is very thorough (I believe by Jerry Graeme, who later published a very good transimpedance book under the Gain Technology name). What is in there are self limiting noise term equations. What we simplified in SBOA122 is we ignored the 1/f region as not a significant part of the integrated noise and we assumed a post RC filter setting a noise integration BW < feedback pole - this simplifies the equations quite a lot and was where the Eq. 3 in say the OPA846 datasheet came from.

Yes, here is the book Mr. Graeme did back in 1995.

https://www.amazon.com/Photodiode-Amplifiers-OP-AMP-Solutions/dp/007024247X

0 Paul Goedeke over 5 years ago in reply to Michael Steffes

TI__Mastermind 30600 points

Hi Manideep,

The advice from Kai and Michael is excellent. Please let us know if you have any further questions.

-Paul

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TLV271: Mistake in Noise Error calculation by hand