CdTe X/Gamma-Ray Detector Electronics and Amplifier Shaping

Considering there are no comments as yet, I am going to take a guess or two.

First of all, what is the noise environment? Normally in an A/D, you put an analog filter, usually a simple RC lowpass filter, at 1/2 the sampling frequency, to keep high frequency noise from getting into the A/D. My first thought was that this might be a noise filter of sorts... after the A/D.

BUT What does the signal coming the pre-amplifier look like? If it is something really wierd, a digital filter can take the time domain characteristics of the input signal and convert it into a pulse (for example). This might make things easier for the microprocessor or whatever comes after the filter.

Hi Sciesis2,

You're right. The signal from the preamplifier is an impulse that has a long tail. This is because the preamplifier is charge sensitive and needs a long impulsive response in order to collect all the charge excited by the quantum.

The shaping amplifier is used to shape this long pulse into a shorter one, so it is at the same time a band-pass filter.

Actually I think I found out the answer. The answer is that the long tail pulse from the preamplifier would be added to the next pulse amplitute. Making unfeasable to detect the charge by looking at the amplitute of the signal.

Thank you anyway. :))

I have a question non-relative to this one, but that you might help me.

Do you know if when analyzed a signal that passes through a filter with Fourier, the transient part of the signal is lost at the output? That would explain why Laplace is then used. Otherwise both transforms would be the same.

The Fourier Transform is a subset of Laplace. If you plot a filter in the S plane, you get a bunch of X's and O's for poles and zeroes. Now imagine a rubber sheet over the plot which goes to infinity for the poles and 0 for the zeroes. Now if you were to slice the rubber sheet along the vertical (j omega) axis and look at the slice, you will find the Fourier transform of the filter.

Thank you Sciesis2, but I know where the Fourier Transform comes from. The main question, does the Fourier Transform of a filter lose information? Otherwise there's no difference between both and they wouldn't have a different name.

v

Id rather agree to #1's anser than yours answer about filter. The filter will be low-pass filter other than band pass filter at the sitation. After preamplifier, the signal has unexpected components over the range of A/D you expected include higher noise. According to sample law, we have to use a low pass filter which is lower than 1/3--1/5 of sample frequency for A/D converter. If you use band pass filter, the important low frequency will be lost. so that you will get a distortion signal after D/A. unless you can restore it by using a clip circuit. l and f have different field.

Yes.I did not say that after the shaping amplifier, there is a base lina restorer, which mainly just adds the DC lost through the band-pass filter.