AD5933

Dear all,

   Could you please discuss why the AD5933 has been provided with the impedance measurement method it holds. There must be some advantages refereeing to it, only that I don't really figure them out. I'm interested in finding out the theory behind it: please kindly provide titles for references (sci. articles, books, patents) comprising the method implemented in AD5933 for impedance measurement. It seems od since it works with floating test impedances, no clear chance to implement differential input and hardly imaginable with current excitation. Thank you for your best suited help! Otherwise (not that it is really a drawback) the digital part seems quite a beauty packed in a tiny (simple) package!

  • 0
    •  Analog Employees 
    on Jun 24, 2015 9:49 AM

    Hi,

    to measure impedance and phase, there are two methods, analog and digital... From the analog point of view, you can use and I/Q demodulator... the main problem is the noise and errors calibration that become a little bit more difficult.

    The second way, it is digitally... and this can be done by an FFT analysis.

    For both methods there are pros and cons...

    Answering your question... you can implement an external AFE to  adapt the part to your requirements...

    Regards,

    Miguel

  • First, thank you for your answer?

    I meant to ask in fact why the measured impedance is placed as one of the impedances of an OP AMP based inverting amplifier. It could have been placed in a bridge, in a ground referred voltage divider or even as part of the feedback impedance. Instead the measured impedance is placed in series with the inverting output. Actually AD has got another capacitance to digital converter which uses the same placement? Why is that, which are the advantages? Besides, let's ignore de I/Q demodulator!

    Thks again for answering more exactly!!!Regards!

  • 0
    •  Analog Employees 
    on Jul 20, 2015 7:39 AM

    Hi,

    Apologies for the delay.. I did not get an alert about your reply...

    answering your question, you can use the impedance in many different ways... in fact, there are few AN in teh web shoeing different configurations...

    The main benefit of the "default" configuration is that the impedance is floating...  so, you are more or less "isolated" from noise problems.

    Best Regards,

    Miguel

  • The original ADI patent you can find on Google Patents: US Patent 7,555,394 "Measuring Circuit and a Method for Determining a Characteristic of the Impedance of a Complex Impedance Element for Facilitating Characterization of the Impedance Thereof." For an article covering some more theory and data on what the chip does you can try googling "ad5933" together with "impedimetric".

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:04 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin