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THS4552: Hardware schematic design problems

Rhea Gao
Expert 2350 points
Part Number: THS4552

Hi,

I have customer who use THS4552. and the customer wants to confirm that the THS4552 output differential signal N terminal is connected to the ADC differential signal P terminal right?

If yes, is there any special configuration required for the ADC?

Many thanks~

  • TI__Genius 11675 points

    Hi Rhea,

    The polarity of the FDA's outputs going into the ADC inputs should not make a difference if they are switched. The way the FDA is laid out with AINP_A from R8 to the netlabel AINP_A on the left side of R9 is correct and usually standard practice.

    Best Regards,

    Ignacio

  • in reply to Ignacio Vazquez Lam1
    Expert 2350 points

    Hi Ignacio,

    The problem is that pin 15 of FDA(THS4552) is the N terminal of the difference, and the N terminal of the output of the op amp is connected to the P terminal of the ADC. I feel that the PN of the difference is opposite between the op amp and the ADC, which will lead to the polarity of the final sampled signal is opposite, right?

    Thanks!

  • in reply to Rhea Gao
    TI__Genius 11675 points

    Hi Rhea,

    I apologize for the confusion; I went with the label on the schematic. You are correct in your assumption, however the polarity into the ADC does not have any impact on the performance itself. Standard convention is the positive output to the positive input of the ADC but can be done either way. 

    Best Regards,

    Ignacio

  • in reply to Ignacio Vazquez Lam1
    Expert 2350 points

    Hi Ignacio,

    If the output P of the op amp is connected to the input N of the ADC, then the data sampled by the ADC should be reversed polarity. What does the ADC need to be configured to get the actual signal?

    Many thanks~

  • in reply to Rhea Gao
    TI__Genius 11675 points

    Hi Rhea,

    To get the signal at the ADC to be the same polarity as the input signal you can flip the outputs going into the ADC inputs on the schematic. I am not sure if there is anything on the ADC side that can flip the input signal, but the easiest way would be to flip the inputs going into the ADC.

    Best Regards,

    Ignacio