ADR441 - Additional Noise Data Requested

   Good morning.  I have a customer currently using the ADR421 as a voltage reference in multiple projects.  The spec on this part indicates 1/F noise of 1.75uV and noise of 80nV/√Hz @1KHz.  The noise graph shows that about same noise is present in the bandwidth of ~ 100Hz…10KHz.

 

      The ADR441 appears to be a better, pin-compatible part with 1/F noise 1.2uV (~31% improvement versus ADR421) and noise of 48nV/√Hz @1KHz (40% improvement).  My customer's bandwidth of interest is DC…80MHz.

 

     QUESTIONS:

 

     1)  Do you have noise graph data over the DC - 80MHz bandwidth for both the ADR421 and the ADR441 (Figure 27)?  If so, can you please provide it to me?

 

     2)  Can you confirm that the noise graphs are obtained without the required 0.1uF capacitor on the output?  My customer has a concern about an implicit low pass filtering effect given the ADR441 output impedance graph shown in Figure 31.

     Thank you.

     Richard A. Pensabene

  • 0
    •  Analog Employees 
    on Aug 22, 2013 3:03 AM

    Question 1) a regulator can only generate noise and amplify ts own reference noise below the loop bandwiuth of the system. Since most regulators (in this case a buffered reference) have gain bw limitations around 1Mhz the noise seen at the output above this frequency is due to thermal noise from resistors transistors and capacitors. As seen in the noise spectral figures these tends to approach an horizontal asymptote and stay at that level over frequency. This is why the plots in the datasheet only show 20Hz to 1Mhz data.

    Question 2) The noise data is obtained with the output cap. The electrical characteristics table on page 3 and the TPC graphs on page 9  list the test conditions including the 0.1uF cap.

    If noise is an important parameter you may want to consider the ADM7160 also, with NSD similar to the ADR441 at 1Khz. There is a bit more data about it in the datasheet.

    If you are looking for substantially lower noise, please have the customer send me an email and I can share data about a new device about to be released (ADM7150)

    Best Regards,

    LucaV

  •      Luca,

         Good afternoon and thank you for the prompt response.  Two follow up questions:

              1)  With respect to the ADR421, since an output capacitor is not required for proper operation, can you confirm that the noise graphs in Figures 24 - 26 are taken without an output capacitor present.  I assume this to be the case since a capacitor is not specified on page 4 of the ADR421 datasheet but my customer would like for me to confirm it for him.

              2)  My customer would like to see the preliminary infomration or data that you have available on the new ADM7150 that you mentioned.  What is the process for doing that?

        

         Thank you.

         Richard A. Pensabene

  •      Dan and Luca,

         Good afternoon and thank you for your help in getting answers to these requests for additonal data.  Thank you.

         Richard A. Pensabene

  • 0
    •  Analog Employees 
    on Aug 27, 2013 11:50 PM

    Richard,

    Regarding your Question:

    "With respect to the ADR421, since an output capacitor is not required for proper operation, can you confirm that the noise graphs in Figures 24 - 26 are taken without an output capacitor present.  I assume this to be the case since a capacitor is not specified on page 4 of the ADR421 datasheet but my customer would like for me to confirm it for him."

    You are correct. We have confirmed that the noise data was taken without an output capacitor present.

    Thanks for the question.

    Dan

  • 0
    •  Analog Employees 
    on Aug 2, 2018 2:26 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin