AD8145 doesn't work exactly.

Dear Sir/Madam,

I need your help.

My schematic:

cf5b8619e13a6629748eb9fcb37b1341.bin

VREF is provided directly by AD5765. I set the common mode voltage of Vin to 0.5 V and the differential mode voltage to 1.0 V.

AD5765's output voltage is set to 0 V.  Than I measure the voltage of AD8145's REF pin. However, it's not 0 V(Of course, AD5765 doesn't work exactly now). The voltage on REF pin has following features:

Its frequency is the same as Vin;

The following pictures show how its Vp-p  varies with frequency:

ddcb67b663c8130f42f55ea6aa07677c.bin

58866f4eb63dcf28941b89e8d64e5890.bin

My question is that why REF pin of AD8145 is not 0 V ?

Parents
  • Hi zhifu,

    Do you know the source impedance of the output that you're using from the AD5765?  REF needs to be derived from a source with very low impedance, otherwise some of the output voltage will appear at the REF pin. If the source impedance is high, the best solution is to use a buffer with bypass capacitors to provide a broadband low-Z source.  Can you connect REF to ground?

    Best regards.

    --Jonathan

Reply
  • Hi zhifu,

    Do you know the source impedance of the output that you're using from the AD5765?  REF needs to be derived from a source with very low impedance, otherwise some of the output voltage will appear at the REF pin. If the source impedance is high, the best solution is to use a buffer with bypass capacitors to provide a broadband low-Z source.  Can you connect REF to ground?

    Best regards.

    --Jonathan

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