IVC102 positive/negative output

[Gorrono]

Hello all,

I am working in a photodetector amplifier design in order to measure currents from around 1pA to 10pA. I want to use the IVC102U as a good solution to improve the SNR.

I am simulating using the multisim models. I checked and the PSpice model is exactly the same that you provide in the webpage.

I decided to use the SWITCHED-INPUT MEASUREMENT TECNIQUE as described in the datasheet. The results look correct a priori. However, I am using a variable DC current in the input and the output is completely independent of that value. It is always a positive-ramp at Vo!!!!

I've tried different configurations, components. Thus, I am wondering if I am missunderstanding something, if the model in Multisim is incorrect or if this configuration is not suitable for this application.

PS. I attach the schematic and output plots!!!

Javier Gorrono

Higher Research Scientist at National Physical Laboratory

[Tien_P]

Hi Javier,

Have a look at the attached Multisim file, I am using figure 3 timing from the datasheet.  In Multisim, I am using the parameter sweep analysis from Simulate>>Analysis to sweep the input current from -20 nA and 20 nA.  From the screenshot, you can see it's possible to get a negative ramp.

 

[Gorrono]

Hi Tien,

Thanks a lot for your answer.

You're completely right. The model perfectly works but only for currents higher than +1nA.

For lower values, like my case (around +5pA), the model is not correctly working.

Therefore, it is confirmed that it is not a problem of configuration (it's been also tested in TINA simulator) but a problem in the PSpice model.

They are working to provide a solution. You can follow the thread here:

http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/288234/1015096.aspx#1015096

Thanks again

Javier Gorrono

Higher Research Scientist

National Physical Laboratory (NPL)