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AD2S1210 excitation buffer question


we are using AD2S1210 eval board for the prototype and it seems to work very well.

now, we are looking into making the circuit for our custom board.

going through CN0276.pdf, CN-0192.pdf, we noticed that the recommended buffer driver circuit always involve a BJT.

on our end, we would like to use FET instead.

Can you please point out any particular reason why BJT is used instead of FET?

what is the downside of using FET as push-pull circuit?  maybe we are missing something.

Thanks and Best Regards,


  • Henry,

    Unfortunately I did not design the output stage on the evaluation board so I don't have intimate knowledge of why the original designer chose to go bipolar instead of using MOS but I fundamentally don't see an issue with using FETs for the output stage.   The only thing I can think of is that ultimately BIPOLAR devices may have allowed for a smaller more cost effective design with respect to achieving the desired current drive.  I will see if I can track down a more definitive answer for you and respond if I find out anything of interest.


  • Sean,

    Thanks for the note.  another question is that i noticed that the eval board has a DC bias up to 5.7v (2.5v ref + 3.75v on inverted input of opamp).  i can see why it was designed like this so that the output signal can be centered around 6v for +12v to 0v driving.  My question is whether i should put the ac-decoupling cap at the output to the resolver excitation coil? 

    do you see any need for that?



  • Henry,

    I do not see the need for any AC coupling between the driver and the resolver primary.


  • BJTs may give an advantage to limiting output current should one of your resolver wires be cut, shorted or mis-wired.