Precision voltage reference with low 1/f noise

[Tommino]

Hi all,

I am looking for two voltage references to produce two rails ( positive and negative) with low frequency noise.

The voltage reference does not need to have a tight output voltage accuracy and long term precision. It needs to be stable over a 1minute period and this is why I am looking for low 1/f noise.

The application is shown in this circuit and I need to get these two references to supply the voltage divider. So far I was supplying the divider with the same +/-5V used for the amplifiers and taken from two linear voltage  regulators ( L78L05ACUTR for the +5V L79L05ACUTR for the -5V): with this setup I get too much noise at the output of the second amplifier which can amplify up to a factor x57.  This noise is not coming from the opamp ( is a low noise opamp from a competitor OPA4205) or the input at pin3 which has been already proven to be noise-free.

 Can you recommend a couple of possible IC to produce two stable references from the +/-5V already present in the circuit? Ideally the ICs should have fixed output at 3 or 4V and be low-cost. The 1/f integrated noise over 0.1Hz-10Hz as low as possible.

Best regards

[Uwe Bonnes]

78xx is not meant for low noise. Look for low noise regulators. B.t.w., there is no "noise-free", there is only (ultra) low noise.

[Tommino]

Hi Uwe,

Sure I meant "noise-free" for my application :)

Do you know pin to pin replacement of

"L78L05ACUTR for the +5V L79L05ACUTR for the -5V"

for low-noise regulators?

[Uwe Bonnes]

Ask a search engine first, or look on the ST. TI. Analog Devices, etc web page.

[Tommino]

Ok sure. I would like also to wait for some other comment from ST engineers

[Jack3]

Hi Tommino, you could consider this solution:
https://www.analog.com/media/en/technical-documentation/data-sheets/lt1236.pdf
Of course you should use the LT1236-5 instead.

Another option:
https://www.analog.com/media/en/technical-documentation/data-sheets/adr4520_4525_4530_4533_4540_4550.pdf

Cheers!

[RobK1]

"Noise as low as possible" and "low cost" are mutually exclusive requirements, you do realise that?

TI's REF35xx series is, to my knowledge, the best compromise between the two.

[Jack3]

Availability is also something to consider.