Is the schematic correct ?  the two outputs are connected  and the two inputs

Where do I find the other end of "FILTER OUT" ?

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  • 0
    •  Analog Employees 
    on Jun 18, 2021 3:26 PM in reply to izhmel

    Hello Izhmel,

    I may be confused as to what you are asking about? The ADAu1452 or the ADAU1466 datasheets will not show any of this because it has to do with interfacing with the codec so it will not be mentioned in the DSP datasheet. The AD1938 datasheet will show the op amps referenced to the CM (common Mode) pin of the codec. That is one way to do it but the other way to do it is to setup a divider between the the AVDD and ground. The purpose is to setup a virtual ground between the single ended power rail so you can use an op amp that uses differential power supplies. As long as the filter is cap coupled you do not have to have this reference voltage be exactly the CM voltage. 

    The Opamp you see in your screenshot is the virtual ground source.

    The way it is drawn does not make it obvious that the two 1K resistors are a divider to setup the voltage mid way then the op amps are setup as voltage followers to provide a low impedance drive. It is a dual op amp so each section drives different input filters which helps keep crosstalk to a minimum. 

    When you ask " where do I find OP_AMP_REF" do you mean on the actual hardware in front of you or in the schematic?

    Dave T

  • Yes the schematic . In the schematic data sheet of the ADAU1466  dose not show this in the schematic . The data sheet of the ADAU1452 shows this . I cant find the opamp ADA48412YRMZ for OP_AMP_REF in the  ADAU1466 data sheet . Are you saying I don't need this as shown in the image ?

    Thanks in advance 

  • 0
    •  Analog Employees 
    on Jun 18, 2021 5:27 PM in reply to izhmel

    Hello izhmel,

    Let's define a few things that I think we are not communicating properly. 

    The ADAU1452 and the ADAU1466 datasheet both do not mention these opamps and do not discuss making a pseudo ground reference. Are you talking about the User guide for the EVAL-ADAU1452RevBZ? The EVAL-ADAU1466 may not be the correct user guide. 

    So what is the issue you are having? The circuits are fine and is a good example of how to interface to the codec. 

    Dave T

  • The user guide I am talking adout of the ADAU1466 . Page 33 and 34 dose not show where in the circuit OP_AMP_REF1 and OP_AMP_REF2  where in the circut the other ends are connected to as shown on page 47 EVAL-ADAU1452REVBZ User Guide (Rev. 0) (

    The immage below shows what is not on the ADAU1466 user guide.