OPA814: Incput current noise

Yoshitaka Kotani

Prodigy 80 points

Part Number: OPA814
Other Parts Discussed in Thread: OPA656

Hello

Regarding the input current noise, the spec says 11fA/rtHz at f>100kHz,

Figure 7-21 shows an increase of 6dB/oct!? It exceeds 11fA/rtHz at about 200kHz.

Is the diagram wrong or is OPA814 increasing processwise?

thank you.

over 2 years ago

0 Yoshitaka Kotani over 2 years ago

Prodigy 80 points

sorry
typo in title

0 Ignacio Vazquez Lam1 over 2 years ago in reply to Yoshitaka Kotani

TI__Genius 16615 points

Hi Yoshitaka,

The increase in current noise as the frequency increases is common in FET devices, which is what we are seeing with this device. The current noise is in the fA/rtHz which in most cases is not the major source of noise in most circuit designs. We do recommend referring to the graph itself for the most accurate representation of the performance for this device.

Best regards,

Ignacio

0 Yoshitaka Kotani over 2 years ago in reply to Ignacio Vazquez Lam1

Prodigy 80 points

Thank you for answering.

I am designing a current to voltage converter.
It was written as an upgrade of the OPA656, but it cannot be used because the input current noise characteristics are different.

thank you

+1 Ignacio Vazquez Lam1 over 2 years ago in reply to Yoshitaka Kotani

TI__Genius 16615 points

Hi Yoshitaka,

Let me look into this for you regarding the older device. I will get back to you as soon as possible.

Best Regards,

Ignacio

+1 Jacob Freet over 2 years ago in reply to Ignacio Vazquez Lam1

TI__Expert 8650 points

Hi Yoshitaka,

The behavior of increasing current noise with frequency is actually intrinsic to FET input devices. A lot of older products did not highlight this performance in their datasheets/models but any FET input device will have this same behavior. Typically it is not noticed in most applications due to the low value of FET input current noise.

Best,

Jacob

Amplifiers

Amplifiers forum

OPA814: Incput current noise