Irradiate the comparator-chip with a beam-current of
50 pA in steps of 3 kRads up to a total dose
of 15 kRad. After every step the Offset-values and Threshold-values
for the 16 different channels has been measurend.
Irradiate the comparator-chip with a beam-current of
50 pA in steps of 3 kRads up to a total dose
of 15 kRad. After every step the Offset-values and Threshold-values
for the 16 different channels has been measurend.
Conclusion :
For the measurement of the Threshold and Offset a input-signal with a width of 100 ns and
a frequency of 10 kHz was used. The output of the comparator-chip is a 3-bit-pattern. It
is the decision which half-part of the Muon-cells has been hit.
The Threshold for every channel was measured varying the voltage of the input-signal. The voltage
at which the 3-bit-pattern disappeared was taken as the threshold-voltage.
The plot below shows the measured values for the Threshold for the different channels every 3 kRads.
From these values a mean and rms of the measured Threshold every 3 kRad was calculated.
The two plots below show the evolution of the mean and the rms of the Threshold measured for
the 16 channels every 3 kRad. To see is an increase of the mean and the rms with increasing
radiation.
The Offset measurement was more complicated. The input-signal was split up into 3 with different
atenuations each of them; the central one having the biggest voltage. Varying the difference in voltages
between the signal on the one side of the central one and the other one on the other side, a flip
in the 3-bit-output can be achieved. The voltage-difference when this bit-flip occurs was defined
as the Offset for the corresponding channel.
The plot below shows the measured values for the Offset for the different channels every 3 kRads. From these values
a mean and rms of the measured Offsets every 3 kRad was calculated.
The two plots below show again the evolution of mean and rms for the Offsets every 3 kRads. Again an increase
of both with radiation was measured.
In the next test 3 comparator-chips were tested for latchup. Therefore the three chips
were irradiated in steps of 5 kRad up to a total dose of 50 kRad. After every step the current
was monitored. The plot below shows the monitored current as function of the radiation.
An increase with increasing radiation-dose is clearly to see. Three different symbols for
the three different chips were used. The measurements for the three different chips are
very consistent. Up to dose of 10 kRad no increase in current is seen. This is twice the
expected radiation-dose of 5 kRad at LHC. Up to 50 kRad an increase in current but no latchup was
measured.
The explained measurements and the obtained results indicate that the comparator-chip is radiation-safe
for LHC purposes.