Simulating AD8333

Hello, My questions are actually basic. I am using AD8333 in my project for bioimpedance measurement. The main aim is to study the food quality using 4 electrode method (auto balancing bridge method). So I wanted to use AD8333 to extract real and imaginary parts of impedance. But I am not getting any proper waveform, its completely distorted. And I wanted to know what would be the relation between the amplitude of output voltage after AD8021 and the impedance value, I am facing some difficulties in understanding that from datasheet. I hope I can use this IC for my particular application. Moreover, I am simulating in Multisim, where I cannot find any LVDS driver so I have used another LNA for LO inputs. Will it be okay? And mainly, I need your help to know if I have made some mistakes with connections or if there are any errors you can rectify for me. Kindly guide me. In my simulation for now, I have used a simple RC parallel circuit to represent bioimpedance in food samples. I am also attaching the picture of the waveform I am getting. Sorry for the circuit being a little messy.

attachments.zip
Parents
  • 0
    •  Analog Employees 
    on Nov 6, 2015 2:36 AM

    Hi Hetashri,

    OK, understand, and I've heard this before. I actually don't have Multisim, ADI has changed to ADIsimPE. However we do have some SPICE experts to support such questions as yours. BTW  there is an LVDS driver shown in the AD8333 data sheet in the eval board section. I'm pretty sure this was tested and works in SPICE but the topic hasn't been raised in several years. From what I can tell from your attached schematic the LNA + ac coupling may be OK but  we have always used dc coupling to the AD8333, and the input circuit shown in the schematic on pg 29 of the attached. Also based in the scope response in your schematic, the output looks a lot like a sine wave with some LO in the output, especially if you are using it at a lower frequency without changing the LP filter in the AD8021 feedback. What is your input frequency? If you're using the circuit in the data sheet bear in mind it was designed for an input frequency of 5MHz. For any other frequency you'll have to scale the filter appropriately.

    Now that I think of it, there is a pretty good (maybe even better) design guide in the AD8339 data sheet.

    I hope some of this helps,

    js

    AD8333_Final_Approval.pdf
Reply
  • 0
    •  Analog Employees 
    on Nov 6, 2015 2:36 AM

    Hi Hetashri,

    OK, understand, and I've heard this before. I actually don't have Multisim, ADI has changed to ADIsimPE. However we do have some SPICE experts to support such questions as yours. BTW  there is an LVDS driver shown in the AD8333 data sheet in the eval board section. I'm pretty sure this was tested and works in SPICE but the topic hasn't been raised in several years. From what I can tell from your attached schematic the LNA + ac coupling may be OK but  we have always used dc coupling to the AD8333, and the input circuit shown in the schematic on pg 29 of the attached. Also based in the scope response in your schematic, the output looks a lot like a sine wave with some LO in the output, especially if you are using it at a lower frequency without changing the LP filter in the AD8021 feedback. What is your input frequency? If you're using the circuit in the data sheet bear in mind it was designed for an input frequency of 5MHz. For any other frequency you'll have to scale the filter appropriately.

    Now that I think of it, there is a pretty good (maybe even better) design guide in the AD8339 data sheet.

    I hope some of this helps,

    js

    AD8333_Final_Approval.pdf
Children
No Data