Two stage amplifier for a plastic scintillator

  • #1
Summary:
Plastic scintillator
When detecting a muon, we can use a plastic scintillator which consists of the components in the diagram attached. I am trying to understand what exactly the "two-stage amplifier" does which is located in the top left corner in the image attached? I am unable to find any information on it online in regards to the particle detector. I understand what the scintillator and the photomultiplier does, but not sure what the two-stage amplifier does.
 

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  • #2
Baluncore
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The PMT output is dependent on many parameters. The output signal will be small. There will be some smaller noise pulses.
The two stage amplifier provides sufficient signal gain to operate the discriminator, which rejects most of the noise, but passes the data pulses.
 
  • #3
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Instead of having one high-gain amplification stage it's typically beneficial to have two lower-gain stages, at least with opamps. This gives you better bandwidth for example.

Also note ond of the stages is inverting, which has different characteristics from non-inverting opamp stages.

I don't know about implenting sensors though so I might be off.
 
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  • #4
DaveE
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It's kind of odd they describe it as a two stage amplifier. Most every amplifier these days is multiple stage (eg. op-amps). The function seems to be "amplifier" how many stages doesn't seem relevant, and I would bet it's wrong if you actually get down to the semiconductor junction level.

In any case amplifiers are ubiquitous in electronic data collection. I suspect you will find amplifiers in every part of that diagram except the PMT and the digital stuff. Wait, on second thought, maybe a PMT is an amplifier too. Plus digital gates are saturated amplifiers.

Without specifications like gain and bandwidth requirements, I wouldn't worry about it.
 
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  • #5
Summary:: Plastic scintillator

When detecting a muon, we can use a plastic scintillator which consists of the components in the diagram attached.
That's the diagram from the Teachspin muon lifetime device, which I have used.

The amplifier has a couple of functions. First, the output of the PMT is best thought of as a current pulse, not a voltage pulse. But by the discriminator, we want voltage. So the first job is convert the current into voltage.

The other is to provide gain. However, a PMT already has gain of perhaps ##10^5## to ##10^6## or greater, so this is often less important, and may sometimes even be skippable. Every amp adds analog noise to the system. Also, each amp has a maximum gain-bandwidth product, so if you tweak them for higher gain, you will lose bandwidth (as others have already noted).

I'm in a somewhat similar situation to you, in that I am considering using the detector module of the Teachspin (which ends just before the amps) in an experiment, and I have already built a (much better, 67 pS precision instead of 20000 pS) replacement for everything after the discriminator, but I still need a replacement for the amps and discriminator. So I need to understand how to design and build those myself.
 
  • #6
Tom.G
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67 pS precision instead of 20000 pS) replacement for everything after the discriminator, but I still need a replacement for the amps and discriminator. So I need to understand how to design and build those myself.
:)) Sounds like you will be busy for a while. Amplifiers at that frequency (14GHz if I did the math correctly) are sold as chips about 1.5mm x 2mm; think microscope, surface mount, wire bond, etc.

Datasheet at:
https://www.analog.com/en/search.html?q=hmc-alh216
 
  • #7
Baluncore
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I'm in a somewhat similar situation to you, in that I am considering using the detector module of the Teachspin (which ends just before the amps) in an experiment, and I have already built a (much better, 67 pS precision instead of 20000 pS) replacement for everything after the discriminator, but I still need a replacement for the amps and discriminator. So I need to understand how to design and build those myself.
You may well have very low jitter in the timing circuits, but the bandwidth of the PMT will limit the signal. Only the initial edge is accurate as the exponential decay of the trailing edge is usually quite variable.

The PMT output is converted from a current to a voltage by a resistor of about 50 ohms at the input to the first stage amplifier. I expect the first stage here is a wideband Current Feedback Amplifier, CFA, is being used with a feedback resistor to convert the PMT output current to a voltage. A second stage will drive the coaxial cable to the discriminator.

What is the part number of the PMT being used for this project? The data sheet will give some idea of the pulse rise-time and the optimum amplifier impedance and bandwidth requirements. The PMT manufacturer will often provide a design example for the wideband amplifier.

Large Dynamic Range Integrated Front-End Electronics For Photomultiplier Tubes
https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.555.4771&rep=rep1&type=pdf
 

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