Silicon Pixel Detector:
A bias voltage of -60 V was applied, which resulted in a current of
app. 0.33 uA. The chip was operated at 2.5 MHz and the measurements have been
made with the following settings:
| RGPR Amplifier |
-2.72V |
|
| RGSM_shaper |
-3.92V |
|
| VBRO |
-3.46V |
|
| HLD_DEL |
-4.80V |
|
| VTRIM |
-1.64V |
sometimes set to -1.14V, no influence seen on the measurement |
| VCAL |
-1.25V |
height of the calibration pulse |
| VGDAC |
-4.02V |
|
| Vc |
-2.89V |
Subtraction of 2.5V gives the effictive threshold. 1V corresponds to 10610
electrons. |
1. Calibration Pulse
In the following figure we can see the response of the readout chip
to a calibration pulse of 13300 electrons injected into the pixel
on column 2 even, row 9. Whenever a single pixel responds the entire double
column is read out. In the first bins the digital header information
(e.g. column number) is coded.
You can also look at a screenshot of the
oscilloscope which shows the analog signal (green). The yellow signal
is a PSI30-controller-intern signal, which indicates the readout.
The lowest threshold which could be set
was 2860 electrons ( VC = -2.77 V) for the silicon and
2440 electrons (VC = -2.73 V) for the diamond sensor.
2. Backplane Pulse, Single Column
Here a backplane pulse of 170mV triggers the readout of a single column.
This pulse height corresponds to 5830 electrons, which is above the
readout threshold of 4140 electrons (VC of -2.89V). Since the pulsheight is just above threshold the responding pixel cannot be identified by eye.
3. Backplane Pulse, All Columns
Now the backplane pulse is increased to 280 mV (which corresponds to 9600
electrons) to generate a readout of all 11 columns. In each column at
least one pixel is above threshold.
A screenshot of the scope shows the timing
of the backplane pulse (blue) before the readout (green) starts.
4. Backplane Pulse, All Columns
With a backplane pulse voltage of 560 mV the chip starts to oscillate
in column 1 and 2 in an almost perfect sine-function.
In the columns 3 to 7 nearly all of the pixel fire. In the higher columns
less and less pixel respond. These are the columns with the most insensitive
cells.
5. Backplane Pulse, All Columns
With a backplane voltage of 2.3 V nearly all pixel respond, except some in
the last columns. The oscillations in the first columns are still visible.
Aug 2 1999, Thomas
Bergauer,
Rudolf Wedenig
