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Extending LVF Frequency Range

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okellycu
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Joined: February 27th, 2014, 4:49 am
Country: Ireland

Extending LVF Frequency Range

Post by okellycu » February 27th, 2014, 5:04 am

I've been using the VLF UTM with some success on my high impedance device
but the range is limited to 10 mHz to 10 Hz .

I'm wondering if its possible to extend the frequency range above 10 Hz?
What would be the upper limit of frequency using the SMUs in this setup?

We also have the CV module for the 4200 but it doesn't have the current sensitivity
range needed (nA range) and produces essentially noise across 1 kHz - 10 MHz when
testing with the setup.

Is there a way to increase the sensitivity of the CV module?

Thanks

Dale C
Keithley Applications
Keithley Applications
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Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: Extending LVF Frequency Range

Post by Dale C » February 27th, 2014, 8:18 am

My preliminary response regarding VLF CV: if UTM does not allow go higher then 10Hz, then there are physical limitation why VLF CV implemented with SMU has frequency limitation.

Regarding standard CV, and since you are getting noise in the range between 1kHz to 10 Mhz, something is not right.. To comment or help , we would need:
- Verification of connections, that includes - of connections/cables, AND confirmation that SHORT and OPEN validation work fine
- Description of the DUT, and what expected values are the cap
- Expected model of the DUT, in terms of equivalent diagram, which include values of the expected cap, plus expected leakage and expected serial resistance
- Expected frequency response, since they were using VLF CV
- Yes, it is possible to improve signal to noise ratio for standard CV. That it what you usually have to do:
o If DUT has high bandwidth and response, and model of the cap is close to parallel, use as high freq as possible. In this case signal/noise is proportional to freq. ALWAYS monitor D= Gp/wCp, D should be < 0.1. Higher values indicate setup issues
o Increase ACV level to 0.1 V.
o Make sure that Low/Sense side of CMTR is on the top plate of capacitor.

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