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DAC8811: Noise density specification

Danilo A.
Mastermind 34720 points

Part Number: DAC8811
Other Parts Discussed in Thread: THS4011

Hi Team, 

Posting on behalf of our customer.

The DAC8811 noise density specification is specified at 12nV/SqrtHz at 1 KHz. It is said that is was measured with a THS4011 as I/V converter.

I use this DAC in a noise sensitive design and I would like some clarifications of this data.

1) The THS4011 input noise density at 1 KHz is spec'd at 12 or 13 nV, then DAC8811 noise should be 0, which of course is not realistic.

2) What are the noise of the reference used and the digital code applied to the DAC ?

3) Then what is DAC8811 alone noise density ?

Regards,

Danilo

  • 0
    TI__Guru 57343 points

    Hi Danilo,

    1. It is important to note that non-correlated noise sources are not strictly additive. 

    2. The reference was likely grounded during this test to remove its contribution.

    3. The noise of the DAC itself is primarily thermal noise of the resistor ladder and Rfb.  Both of these have a nominal resistance of 5kΩ, so you could estimate about 9nV/rtHZ at 1kHz.  

    The THS4011 has a pretty thorough noise analysis in the Application Information section.  I believe if you assume the 5kΩ resistance in the input and feedback of that formula, you will get the nominal 12nV/rtHz value.

    Thanks

    Paul