Hello.
This is my first post, so I would like to say hi to everybody!
I am an Experimental Particle Physics Ph.D. student but I have a background in Theoretical Primordial Cosmology. So I am pretty new to the field.
Anyway, I am here because I am trying to understand the inner functioning of an ASIC that we are currently using in our experiment. The ASIC is named SPIROC and is developed by the Omega company. The experiment I am collaborating to is called T2K (but it isn't relevant for the present discussion)
Despite SPIROC being almost 10 years old, it is still under active development. This is one of the reasons, as you can see from the linked webpage, why any manual or official documentation doesn't exist. Believe me or not, all the physicists who I know that use or have used SPIROC, learned about it by word of mouth, so they basically only know how to operate it but have little knowledge of its inner functioning or its most subtle properties.
Anyhow, by searching online I stumbled upon various articles dealing with SPIROC and now I am reading through them and trying to put all the pieces together. But there is a part of an article that goes against what I have learned about pre-amplifiers until now. So here I am. I will tell you what doesn't make sense about that article and I hope that here there is someone who could kindly tell me if I am wrong in doubting the article authors or if their result is indeed strange.
As far as the present discussion is concerned, I am just focusing on the pre-amplifier stage of SPIROC (that is always used to read Si Photon Detectors). In particular on the dependence of the pre-amplifier noise on the feedback capacitance and on the shaping time.
The article in question is freely downloadable from arxiv.
As I said On page 6 and 7 there are two figures that I don't quite understand. I will analyze them one at a time ...
The first figure is this (page 6 figure 3):
In the article, it is specified that the expected dependence of the noise on the feedback capacitance is 1/Cgain, where Cgain is the feedback capacitance.
Now, in every other reference literature that I consulted, it is written that the noise (equivalent noise charge) is always increasing with increasing input capacitance (including the feedback capacitance). For example, here it is shown that any kind of electrical noise grows almost linearly with the input capacitance of the pre-amplifier, as also shown in this graph:
Going on to the second picture from the article, it is shown the dependence of the noise on the shaping time of the linear amplifier.
The shaped signal is a semi-gaussian obtained through a CR-(RC)^2 equivalent circuit. The shaping time can be trimmed from 25ns to 175ns.
In the famous book by Knoll it is shown that the dependence on the shaping time should have a minimum and not be monotonic:
Thank you for reading this long post. I really thank in advance whoever would help me clear my doubts.
This is my first post, so I would like to say hi to everybody!
I am an Experimental Particle Physics Ph.D. student but I have a background in Theoretical Primordial Cosmology. So I am pretty new to the field.
Anyway, I am here because I am trying to understand the inner functioning of an ASIC that we are currently using in our experiment. The ASIC is named SPIROC and is developed by the Omega company. The experiment I am collaborating to is called T2K (but it isn't relevant for the present discussion)
Despite SPIROC being almost 10 years old, it is still under active development. This is one of the reasons, as you can see from the linked webpage, why any manual or official documentation doesn't exist. Believe me or not, all the physicists who I know that use or have used SPIROC, learned about it by word of mouth, so they basically only know how to operate it but have little knowledge of its inner functioning or its most subtle properties.
Anyhow, by searching online I stumbled upon various articles dealing with SPIROC and now I am reading through them and trying to put all the pieces together. But there is a part of an article that goes against what I have learned about pre-amplifiers until now. So here I am. I will tell you what doesn't make sense about that article and I hope that here there is someone who could kindly tell me if I am wrong in doubting the article authors or if their result is indeed strange.
As far as the present discussion is concerned, I am just focusing on the pre-amplifier stage of SPIROC (that is always used to read Si Photon Detectors). In particular on the dependence of the pre-amplifier noise on the feedback capacitance and on the shaping time.
The article in question is freely downloadable from arxiv.
As I said On page 6 and 7 there are two figures that I don't quite understand. I will analyze them one at a time ...
The first figure is this (page 6 figure 3):
In the article, it is specified that the expected dependence of the noise on the feedback capacitance is 1/Cgain, where Cgain is the feedback capacitance.
Now, in every other reference literature that I consulted, it is written that the noise (equivalent noise charge) is always increasing with increasing input capacitance (including the feedback capacitance). For example, here it is shown that any kind of electrical noise grows almost linearly with the input capacitance of the pre-amplifier, as also shown in this graph:
Going on to the second picture from the article, it is shown the dependence of the noise on the shaping time of the linear amplifier.
The shaped signal is a semi-gaussian obtained through a CR-(RC)^2 equivalent circuit. The shaping time can be trimmed from 25ns to 175ns.
In the famous book by Knoll it is shown that the dependence on the shaping time should have a minimum and not be monotonic:
Thank you for reading this long post. I really thank in advance whoever would help me clear my doubts.
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