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AD9235 setup

Let me confirm how to set up AD9235 (12bit AD Conveter) with AD8132(Differential Amp.).

My question is the relation between SENSE, VREF in AD9235 and VCOM in AD8132.

In my understanding, VREF can be connected with external voltage as an input.

So if I set the SENSE as AVDD, I can get 2 x VCOM accordingto the data sheet.

If I set the VCOM as +1.5V by volume, I can get 3Vp-p output from AD9235, am I correct?

Or I may be able to set SENSE using external resistor(R1:1K, R2:2kohm) to get VREF as 1.5V

like Figure40. Then I can get the same 3Vp-p, am I corrct?

  • Hi,

    You are correct that you can provide an external VREF when SENSE is tied to AVDD.  The AD9235 is characterized for operation between 1 to 2Vpp differential.  Greater voltages like 3Vpp differential can be accommodated, but distortion performance will degrade.

    The internal reference generator has not been characterized to output 1.5 V, so I would not depend on that to generate the VREF in that case.

    You may gain some headroom with higher analog supply voltage, which in-turn will increase the Vcm that the AD9250 outputs and give the input sampling circuitry a little more margin. 


  • Thank you for your comment. (Sorry to be late)

    1. I was a little bit surprised to know that I cannot get 1.5V at VREF. So I should forget the R1,R2 setup solution.

    2. I will use AD8132 to set VCOM as 1.0~1.2V and set SENSE in AD9235 as AVDD as well. Also I would increase analog input as you mention to get 2.5V typ. as AD9235 output.  I definitely need 2.0V min as output. Because I have to connect AD9235 with FPGA(CMOS) via D-FF which requires 2V as VOH.

    If you have any comments on this, please let me know otherwise I will proceed to PCB design.

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