The Cathode Strip ADCs.
A Study Anode Preamplifiers Performance vs Cathode ADC Signal.
The cathode strip ADCs.
- This is NOT an analysis of P2 Cathode Strip ADCs performance. To see how
anode signal depends from the amplitude of the cathode strip signal the simple
analysis of cathode strip ADC data was done. The data are from HV/Threshold
scan runs (344-371) taken on GIF beam (GIF source OFF).
- To get a charge induced on one cathode strip a sampled distribution was used
(Event display) . The
charge was measured as a sum of ADC counts in 6 time slices including slice
with the max. ADC. As a pedestal the ADC count, averaged over the rest
8 slices was used. Example of the pedestal distribution for the strip 24 is in
the (Plot) .
- The total induced charge is
shared typically by 2-3 cathode strips
(Event display) . The
negative values
are due to noise fluctuations and are not important in our analysis. For the
total charge induced in the cathode strips in the given plane the sum of the
charges over 3 cathode strips including the strip with max. charge in the
center was taken.
No calibrations and cross talk corrections were done to simplify the analysis.
The distribution of the max. charge per strip is in this
Plot and the
distributions of the
total charge for each plane are
here . The fit was done
by two semigaussians with common center.
The distribution of cathode strip number with max. charge presents
the beam profile in
each plane.
The 32-nd strip in each plane (and 17 in plane 5) look as the most noisy strips
when the beam missed the readout strips (a bug in my code is also possible).
Their contribution is 2 times less when the max. charge is required to be
greater than 200 counts of ADC.
- To distinguish two hits in one plane the following distribution can help
(see the Plot) . Here the
charge
from 3 strips with max. charge is plotted versus the fraction of the charge
defined as the ratio of the 3 strip charge to the sum of charges over all 16
strips. The z-scale is logarithmic. Events wit small ADC channel numbers
( < 100 ) are the noise. The area at charge > 100 and fraction > 0.6 are
events with single hit. The small grass to the left and to the right is likely
to be events with more than one hit.
- The dependence of the mean of the induced charge (ADC > 100) vs cathode
strip number is in the
Plot . The
distributions are rather flat.
- The dependence of the induced charge (as fitted semigaussian center) vs HV
is in the
Plot .
The Anode signal vs the Cathode Strip ADC signal.
- To see how sensitive the anode time distribution to the amplitude of the
signal is the mean of anode TDC (nsec) distribution was plotted vs the cathode
strip induced charge (measured in ADC counts)
(Plot) .
In general there is no any dependence (the max. spread is +-1-2 nsec) though
anode channel 12 in the plane 4 has some indication of it.
- The anode time distributions also don't look to be dependent on the cathode strip
number
(see Plot) .
The deviation of the mean is well within +-2 nsec.
- Having measured the cathode strip induced charge we can plot anode efficiency
as a function of the cathode charge at different thresholds. If we know how
to link the cathode induced charge measured in ADC counts to the input charge
of the anode preamplifier measured in fC we can check the calibration of the
anode thresholds made on the bench (can we ?). An example of such approach is
given on the next
Plot , where efficiencies averaged over 3 anode channels in each plane are presented as a function of
total cathode strip charge, measured in ADC counts. The raising eff. at ADC<200 corresponds to events when track missed the readout region of cathode strips. The errors are from binomial distribution.
Note that the plane 3 has the plateau starting at much higher amplitude of the cathode signal.
- As a measure of the anode threshold in terms of cathode charge we can use the ADC channel corresponding to 50% anode efficiency.
The distributions were fitted by the Fermi function eff=100%/(1. + exp(-(ADC - A)/B)) in the region
of 200 < ADC < 600, where parameter A is the ADC channel, corresponding to 50% anode efficiency and B
is the slope (see the A parameter fitted values for different planes on the
Plot ). Though at given amplitude of the
anode signal the induced cathode charge could be different, the parameter A should be one and the
same for different planes if the anode thresholds and cathode electronics
gains are
the same.
- The same distributions for anode chips 3, 5 and 6 from card 1 are presented on the
Plot . Note that in the muon beam at GIF the channels only from these chips were illuminated. Plane 3 was excluded. The result does not confirm the statement that the thresholds for
the chips on one side of the board are much higher than in the center.
- to be continued...
Last modified: Mon May 31 13:20:00 CST 1999
teren@fnal.gov