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ACF2101 noise modeling

Dylan C-W
Prodigy 30 points

Other Parts Discussed in Thread: ACF2101

Hi, I have a use for the ACF2101 switched integrator that does not fit the datasheet usage. Instead of integrating photodiode current I am measuring charge from excess charged particles hitting a halo ring. It's part of the beam diagnostics system for a particle accelerator.


From what I've seen, there is no characterization of the input voltage noise or current noise of the internal amplifier, only typical noise gain analysis in the various states of the integrator.

Also, I'm surprised that the switch noise is listed as uncorrelated, there must be also a correlated component from charge injection, corresponding to sampling frequency?

  • 0
    TI__Guru* 93105 points

    Hi Dylan,

    Sounds like an interesting application. I sorted through the 20+ year old ACF2101 characterization information looking for anything that might answer your question about a correlated noise component, but didn't find any. 

    The data sheet specifies the output noise while in each of the ACF's different modes. Nothing is being switched while in any one of those modes and the noise would be uncorrelated. However, if the device is operating dynamically with the Hold, Reset and Select switches switching at particular rates there will be correlated noise associated with the charge transfers.

    Regards, Thomas

    PA- Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 30 points

    Hi, thanks for the reply. In thinking about it, the switching noise is irrelevant, other than some DC charge offset due to injection from the switches.


    That leaves just the input voltage and current noise of the internal op amp as a contributor to noise on the integrator held output, and the thermal noise from the resistance of the switches (which is given).