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GUI Description
Test Acquire:
Test Acquire attempts to inject every pixel on the Selected Chip.
The pixels that respond are displayed in the Chip Array portion of the GUI in red.
Use the Kill and Inject masks to
isolate pixels of interest.
Hit Map:
When Hit Map is activated a timer is started. Everytime the timer goes off, effectively, Test Acquire is run. The only difference is that the hits are maintained in a running sum and
displayed with varying color intensity to the Chip Array. If the user right-clicks on a chip of interest to open up the Zoom feature, Hit Map
displays the results in the Zoom window. To save the results of Hit
Map to file, the user must set the Save Hit Map checkbox prior to
running the test.
Laser Scan:
When the
user presses the Laser Scan button a timer is started. Each time the
timer goes off, a Laser Scan is run.
Absolute Calibration:
The
Absolute Calibration Button conducts the absolute calibration
process.
Inject Scan:
Based on the parameters selected in the S-Curves Dialog, Inject Scan injects the Selected Chip through
a
range of pulser voltages. When Auto is selected, Pinga attempts to automatically find the best start and stop pulse voltages for the chip calibration scan.
The Auto-Scan Parameters, accessed through the Set Button, can be tuned for
optimal performance. If the Save checkbox is checked, then after a
completed Inject Scan, a .cal file is saved to disk with the results
of the scan. The
Test File name is the string in the Filename textbox. After the
.cal file is created, the user can press the Analysis button to
view the statistics of the chip in question.
Inject Scan is most useful in calibrating chips; a discussion of what
calibration means is now presented:
Fig. 1
The purpose
of calibrating a pixel chip is to gain
information about the chip's Threshold and Noise. Threshold
refers to the level of charge necessary for the chip to respond; Noise refers to
the width of the response band. The
first step in acquiring the Threshold and Noise
is to attain S-Curves for every pixel on the chip. Above, in
Fig. 1, is an example
S-Curve for a single pixel. The x-axis
is the amount of charge injected, in electron units, and the y-axis
is the number of responses out of
100 pulses. In order to get this single
S-Curve, the pixel cell was pulsed 100
times at each level of charge, ranging
from less than 1500 electrons to greater than 3000 electrons, and the number
of responses out of 100 was recorded for each
step. In the figure, each data point is shown in red. Finally, the
S-Curve is fit to the data - displayed in the figure as a
black line. It is important to note that the accuracy of the fit
is related to the resolution of the data points. The closer
together the pulses, the more accurate the fit; however, unfortunately, the
more time consuming the process. This fit was done using a pulser step size of .001V.
Fig. 2
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Fig. 3
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The
next step is to differentiate the S-Curve to arrive at a Gaussian distribution.
An example Gaussian is shown in Fig. 3 with a depiction of
Threshold and Noise for the cell. The blue, vertical lines in
Fig. 2 are indicating the region of meaningful data. It can
be seen that outside this region, the slope of the S-Curve fit is
unchanging, and therefore the derivative is zero. Ideally, only data from within the
interest area would be taken. However, each of the 2816
cells may have its own Threshold and Noise values, so it is difficult to optimize
the range of pulser values
for the Inject Scan such that the
meaningful data is kept and meaningless data removed.
On a side
note, it is for this purpose that the Auto-Scan feature was
created. Auto-Scan attempts to find the pulse range that will minimize the number
of meaningless samples. The net effect is that time is saved.
It can be imagined that if a user has
to manually adjust the ranges for the
calibrations of eight chips, the user will likely just select a wide pulser range to save time.
Auto-scan is nice because it minimizes
human effort and computer effort -
no time is spent by the user locating the
interest area, and no computing effort is wasted recording
data outside the interest area. It is important to note that 100 pulser steps
take approximately 15 minutes to complete - so every step saved helps.
Fig. 4
Returning
to the calibration process, once the Gaussian, as shown in Fig. 3,
is calculated for every cell, the 2816 values
of Threshold and Noise are then accumulated into two new distributions.
A Threshold distribution and a Noise distribution as shown in Fig. 4. Fig.
4 is a snapshot from the Root application. The sample data
is show in red for the
Threshold
distribution and in blue for the Noise distribution. Now, two new Gaussian distributions
can be fit to the Threshold and Noise information
- shown as black in the figure. Finally, the desired calibration statistics can
be ascertained from the new Gaussian curves: The
Threshold mean and dispersion, and the Noise mean and dispersion. In
the Root application
these statistics
are
displayed as in Fig. 5, below:
Fig. 5
And, the chip calibration is complete.
In Fig. 6 the shape of the pulse used in calibration is depicted. This is the pulse that is injected to each cell 100 times in order
to determine the Threshold and Noise of the cells. The signal has a positive offset of 2 V. When the size of the pulse was referred to before, more explicitly what was
being referred to was the fall length of this saw tooth shape; in Fig. 6 the pulse size is .45 V. It can be seen that the signal drops 450 mV and then slowly rises to 2 V again:
Fig. 6
The fall time for the pulse is depicted in Fig. 7, below. The view is zoomed and cursors are used to determine that the fall took approximately 5.2 ns:
Fig. 7
Test Files:
The filename entered here in the Filename textbox is the filename given to every test file that is saved. The extension changes based on which test is being run, but the name remains the same. The
extensions include .gif, .pdf, .rpt, .cal, .fit, and .abs. The *.cal file is generated when Inject Scan completes a run. The .gif, .pdf, .fit, and .rpt files are generated by
Analysis .
All files will be created in the "/Pinga/FILES/CALDATA/" directory.
Stop Toggle:
Pressing this button will toggle the Stop Button. If the Stop Button is open, toggling will close it. Alternatively, if the Stop Button is closed, toggling
will open it and give it focus. The current status of the Stop Button, either "opened" or "closed" is saved to the configuration file when the
Save Configuration button is pressed, and the user's preference will be loaded again upon execution of Pinga or activation of the
Load Configuration button.
When Pinga exits, Pinga should automatically close the Stop Button;
however, if it is necessary to manually close the Stop Button, the
user should click the Stop Button application from the Taskbar
to give the Stop Button focus, and then press the Esc key.
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