# Has anybody tried this transimpedance amplifier?

Started by November 16, 2023
```https://www.newport.com/p/70710.

Is the input current noise lower than that of the LT1028 below 1 kHz?

Regards,
--
Jean-Pierre Coulon

```
```On Thu, 16 Nov 2023 16:26:52 +0100, Jean-Pierre Coulon
<coulon@cacas.pam.oca.eu> wrote:

>https://www.newport.com/p/70710.
>
>Is the input current noise lower than that of the LT1028 below 1 kHz?
>
>Regards,

You can buy opamps with noise less than 1 fA/rthz.

LT1028 is bipolar, 1000x that noise.

```
```On Thu, 16 Nov 2023, John Larkin wrote:

> You can buy opamps with noise less than 1 fA/rthz.

The AD549 has a promising current noise. I must experiment because of is
undocumented voltage noise at the frequencies I want.

--
Jean-Pierre Coulon
```
```On 2023-11-16 15:45, Jean-Pierre Coulon wrote:
> On Thu, 16 Nov 2023, John Larkin wrote:
>
>> You can buy opamps with noise less than 1 fA/rthz.
>
> The AD549 has a promising current noise. I must experiment because of is
> undocumented voltage noise at the frequencies I want.
>

If you post a bit more about what you're actually trying to measure, we
can probably be more help.

A TIA with 4 pA/sqrt(Hz) noise, 100 kHz bandwidth, and 10**9 ohms
transimpedance will have an output noise floor of

E_N ~ 4e-12*1e9*sqrt(1e5 * pi/2) = 1.6 Vrms.

[The pi/2 is the ratio of the noise bandwidth of a 1-pole rolloff
(1/4RC) to its 3-dB bandwidth (1/2piRC).]

Viewed on an oscilloscope, that'll look like a 6-V wide stripe down the
middle of the display, with outliers up to +-5V at least.

Not exactly your state-of-the art low noise amplifier!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

```