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AD9837, AD8302, AD7357, 10-200kHz Impedance Analyzer

Question asked by kampianakis on Jul 11, 2014
Latest reply on Jul 16, 2014 by kampianakis

Hello,

 

I am developing an impedance analyzer for a PZT element (capacitive) and I am looking for some advice on the usage of the AD8302. The overview of the system that I am working with is attached (overview.jpg).

 

Particularly, I am using the AD9837 for the frequency generation. The signal is driven to a high pass filter to remove the DC component and then to a buffer to compensate for voltage drops. The signal then is driven to the device under test (DUT) which is the PZT element.  In order to characterize the impedance of the DUT the voltage at the input and the current at the output is measured. Therefore, for the conversion of current to voltage a transimpedance amp. is used. The signal from the transimpedance converter and from the input to the DUT are driven to the AD8302 in order to convert the amplitude and phase difference to respective DC voltage signals. The latter are driven to the AD8357 ADC where they are converted to digital signals and received by a Raspbery Pi module that controls both the ADC and the DDS.

 

The setup that is utilized is described in many papers some of which are included here:

 

Paper1, Paper2, Presentation

 

I have some questions regarding the implementation of@ this setup:

 

Q1: Do I need to utilize attenuators at the inputs of the AD8302 if I ensure that the inputs are such that they do not exceed the maximum limits of -13dBV?

 

Q2: Will I need to implement some sort of impedance matching at the AD8302 other than using a large enough capacitor at the inputs? If yes, could you provide a method for determining the component values at those frequencies?

 

Q3: Are the directional couplers necessary for such low frequencies? If yes, could you provide a product that is suited for the job ? I have done some research with no results for the specific frequency.

 

Q4: What is the best method to interface the Pi to the AD9837. In windows I utilize the GUI. However, the whole control is implemented in linux (raspian) and therefore the GUI is not available. I have seen  the drivers posted at this link but I didnt quite figure out with what device can they be used. Is the FTDI FT2232H a suitable device? Are there any other devices suitable for interfacing the Pi with the AD9837?

 

Q5: Do you have any particular suggestions for the transimpedance amplifier and the buffer? I currently use the the old TL082 dual op-amp which was available at the lab. However the noise characteristics and the frequency response is not very good. Can you suggest an alternative ?

 

baban79 has posted some extensive questions on the subject and his help on the subject would be most valuable.

 

Thank you very much in advance.

 

Best regards

Lefteris Kampianakis

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