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AC current meas. on Keithley 2410 SMU

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Etaigr
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Joined: November 22nd, 2017, 6:57 am
Country: Israel

AC current meas. on Keithley 2410 SMU

Post by Etaigr » November 22nd, 2017, 7:24 am

Hello.

I'm trying to use Keithley 2410 SMU to measure the current through a photodiode, generated by the illumination of a LED.
The light signal is a sine wave with an offset, i.e. the result is AC+DC current through the photodiode.

A few questions:
1) The current readings on screen are approximately stable. In case of AC current, how are the measurements averaged? RMS or AVG of the samples?
2) The Sinusoidal modulation is of GHz's . What is the sampling rate of the Keithley? Can it handle the frequency of current changes?

Thanks!
Etai

Andrea C
Keithley Applications
Keithley Applications
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Re: AC current meas. on Keithley 2410 SMU

Post by Andrea C » November 26th, 2017, 12:48 pm

The SMU uses an integrating A/D converter (ADC).
The speed of the ADC is affected by all the various settings. If using fixed ranges, then auto zero and NPLC settings are predominant influences.
For good rejection of 60Hz noise, operate at 1 NPLC (or larger integer). Smaller NPLC will yield faster measurements at expense of more noise and larger variance. Data sheet has accuracy de-rating factors based on speed.

Max sample rate will be only single digit KHz (into internal buffer). Additionally, the analog bandwidth is unlikely to be in the GHz range.

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