Charge-Sensitivity in Preamplifier

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Discussion Overview

The discussion revolves around the characteristics of a preamplifier, specifically its charge sensitivity and how to determine its time constant. Participants explore the implications of linear output voltage increases in response to pulse voltage and width, as well as the behavior of the output voltage over time.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes their observations of a preamplifier's output voltage increasing linearly with both pulse voltage and width, questioning the implications of this behavior.
  • Another participant inquires whether the original poster is designing the amplifier or reverse engineering existing equipment.
  • A participant confirms that the measurements indicate a charge amplifier, prompting a request for clarification on why this is the case.
  • One participant argues that the term "charge sensitive" may not be the best descriptor, noting that most amplifiers respond to charge introduction, but charge amplifiers uniquely indicate accumulated charge over time.
  • It is suggested that charge amplifiers function as integrators, effectively measuring the number of charged particles or conditioning signals from charge-displacement sensors.
  • Discussion includes the possibility of charge amplifiers being self-resetting or externally resettable.

Areas of Agreement / Disagreement

Participants generally agree that the measurements indicate characteristics of a charge amplifier, but there is some contention regarding the appropriateness of the term "charge sensitive" and the specific behavior of different types of amplifiers.

Contextual Notes

Participants express uncertainty about the time constant of the preamplifier and the nature of the sharp dip observed in the output voltage, which is described as potentially being an artifact.

Who May Find This Useful

This discussion may be useful for individuals involved in the design or characterization of preamplifiers, particularly in laboratory settings, as well as those interested in the principles of charge amplification and signal conditioning.

dlbi
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How I tell if a preamplifier is charge sensitive? I have data taken from a preamplifier that is fed a pulse from a voltage pulser that is fed through a current generator.

As the pulse voltage was increased the preamp output voltage increased linearly. As the pulse width was increase the preamp output voltage increase linearly also.

What should I make of this?

Also how to I determine the time constant of this preamp? The output voltage of my preamplifier does not appear to decay over time... there is a very sharp dip after the preamplifier's maximum output voltage, but I figure that is just some artifact of some sort...
 
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Are you designing this amplifier, or attempting to reverse engineer someone else's equipment?
 
Mike_In_Plano said:
Are you designing this amplifier, or attempting to reverse engineer someone else's equipment?
I am characterizing a preamp in my lab.
 
Your measurements have accurately described a charge amplifier.
 
Mike_In_Plano said:
Your measurements have accurately described a charge amplifier.
Thank you! By can you explain to me why? I figured it was charge sensitive, but I'm having a hard time grasping why.
 
I don't know if the expression "charge sensitive" is a very good description because most any amplifier will react to introduction of charge.

The charge amplifier is unique in that the output indicates the accumulated amount of charge (i.e. current x time) that has been injected over a prolonged time.
Other amplifiers typically react to a charge injection and then quickly settle back to zero.

So, a charge amplifier is an integrator.

It is effective at indicating the number of charged particles that have been accumulated on a surface, the number of photons / ionizations that release charged particles in detectors, or conditioning the signal from charge-displacement sensors (such as a quartz accelerometer)

The charge amplifier may be self-resetting (i.e. slowly settling back to zero), or externally reset via a signal commanding it to reset to zero.
 

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