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Transimpedance(I-V) converter opamp suggestion

Question asked by kampianakis on Jul 15, 2014
Latest reply on Aug 6, 2014 by kampianakis

Hello,

 

This is a follow-up from the discussion here.

I have copied most of the text from there, apart from the answered questions.

 

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 here.

 

Particularly, I am using the AD9837 for the frequency generation from 10-200kHz. 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 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 ?

 

Q2: What are the characteristics of the amplifier that I should look for?

 

Q3: I have seen  In order to drive a large capacitive load (~10nF) is it good practice to utilize a resistor in series with the load? If yes, is there any rule of thumb regarding the value of the resistor (AD712 uses 100Ohm)

 

Q4: I need to attenuate the signal that is input to the AD8302 down to -30dBm (ref 50 Ohm), can you suggest an apropriate attenuator setup  using opamps, preferably the ones from Q1?

 

Any other comments and suggestions regarding the setup that I have described are more than welcome.

 

Thank you very much in advance.

 

Best regards

Lefteris Kampianakis

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