Hi,

I intend to use the AD5790 DAC for a precise DC voltage source. The datasheets says that the noise in the 0.1Hz to 10Hz bandwidth is 1.1uVpp (datasheet page 3 and 15).
Further there is a noise density plot on page 16. I estimated the 1/f corner frequency to be about 7Hz.

If I integrate the noise density from 0.1Hz to 10Hz I got a noise of about 45.8nV rms.

Calculation:
Vn rms = Vnw * sqrt( Fc * ln(Fc/FL) + (Fh- Fc) ) = 8 *sqrt(7*ln(7/0.1)+(10-7)) = 45.8nV rms

Vnw = voltage noise spectral density in the white region = 8nV / sqrt(Hz)
Fl = lowest frequency of interest in the 1/f region = 0.1Hz
Fh = highest frequency of interest in the white region = 10Hz
Fc = 1/f corner frequency

Multiplying the rms noise with a factor of 6.6 gives roughly the pk-pk noise. 45.8nV * 6.6 = 302.3nVpkpk
This should correspond with the pk-pk noise given in the datasheet. But it does not. The datasheet specifies a pk-pk noise of 1.1uV which is 3.6 times more.

Where does this discrepancy come from?

Best regards,
Lukas

• Hi Lukas,

Someone is currently looking into your query and will respond as soon as possible.

Cheers,

Ivan

• Thank you very much.
For my application having low 1/f noise is very important. I'm currently evaluating also the DAC11001A from TI which has according the datasheet lower noise in the 0.1Hz to 10Hz bandwidth.

Best regards,
Lukas

• Hi,

Is there any progress on my query?

Best regards,

Lukas

• Hi Lukas,

I'm still following up with the responsible engineer, I'm expecting to receive the response tomorrow morning.

Cheers,

Ivan

• Hi Lukas,

The difference between the two measurements is the setup and how the final value was gathered.

NSD: The noise at the reference input pins were removed, effectively leaving an NSD plot of the device itself.

0.1Hz-10Hz: effective 0.1-10Hz noise including the noise at the reference input pins.

Cheers,

Ivan