Re: FDC/CDC ASIC meeting minutes

[Yves Van Haarlem <yvhaarle@ernest.phys.cmu.edu>]

Hi Fernando,

I did the measurement we discussed: measuring the shaper-gain with signals 
within the linear range of the preAmp. I used cosmics (because we know 
that the Fe-55 X-rays will saturate the preAmp) and selected signals which 
are in the linear range of the pre-amp (<450 mV amplitude), for different 
HV settings. I did 3 measurements for every HV setting - I also took care 
that the signals had kinda the same shape (no noise) and that there were 
no double pulses that were close to each other. I saved all traces in case 
somebody wants to look at them. I'll list the average shaper gains (out of 
three measurements), I measured:

HV(V) | shaper-gain
==================
1600  | 2.3
1650  | 2.4 
1700  | 2.3
1750  | 2.5
1800  | 2.4
1850  | 2.1
1900  | 2.1
1950  | 2.1

==> the error on the shaper-gain is around 0.1 (sigma/sqrt(3)), I first 
measured the amplitudes at the different HV settings and afterwards 
calculated the shaper-gains to keep myself as unbiased as possible.

I believe the shaper gains are fairly constant and indeed the shaper has 
the same gain for equally shaped signals. As I understood this is the same 
measurement the FDC did. I am wondering if they would see the same shaper 
gain behavior as a function of HV if they took an average over a lot of 
signals for different HV settings (using the Fe-55 source) as I did before 
this measurement, as that gain should be constant if the Ar peak is in the 
linear range of the preAMP for all FDC HV settings.

If I have the interposer with the charge division I could repeat the 
measurement with Fe-55 source (if it is in the linear range of the 
preAmp).


Cheers and have a nice weekend,
 	Yves



                           /--------------------------------
                          /   Yves Van Haarlem
        _--~~--_         /
      /~/_|  |_\~\      /      Carnegie Mellon University
     |____________|    /        Department of Physics
     |[][][][][][]|:= /          Wean Hall room 8404
   __| __         |__ \       	 Pittsburgh, PA 15213
  |  ||. |   ==   |  | \           USA
(|  ||__|   ==   |  |) \
  |  |[] []  ==   |  |   \   	    Tel.:   +1 412 268-6949
  |  |____________|  |    \                  +1 412 641-9252
  /__\            /__\     \	      Fax.: +1 412 681-0648
   ~~              ~~       \-----------------------------------