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THS3001: THD in real test is large than datasheet

Part Number: THS3001

Hi colleague,

Our customer encounter below issue:

After the signal output by the DAC passes through the THS3001, the total harmonic distortion of the 1MHz signal is -68dB. From the data sheet, the THD is less than -96dB.

 So is there any problem with the op-amp? Thank you.
The op-amp circuit is as follows: The front stage of the op-amp is the DAC current output; the rear stage is the filter.

  • Morning Mr. Su, 

    Cannot answer this question without the full load model and output swing. 

    I would say you should reduce those input 1kohm  to the IN+ nodes nodes to 20ohms. They probably put them there thinking they were getting bias current cancellation, not possible on a CFA like the THS3001. 

    Also, you may have stability issues due to the relay capacitance on the lower amp inverting node. Would need a model for that. 

    This I think are the plots you are referring to - note these are only 2Vpp out