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RTS effect on fake hit rate in Mimostar3

Xiangming Sun

L. Greiner,M. SzelezniakH. MatisT. StezelbergerC. VuH. Wieman

Lawrence Berkeley National Lab

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Random telegraph signal (RTS) in Mimostar3

Random telegraph signal (RTS) found in the Mimostar3 sensor. The plot shows the continuous ADC sample for a pixel with RTS noise. One can see two jumps in ADC value, which are Random telegraph signals

The time length of rising region is similar with the discharge time constant of the charge collecting diode. ~100ms

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RTS shape

a typical RTS is composed by three types of regions, rising region, plateau and descending region. We call the different of plateau and background as the RTS height. Only the descending region can produce positive CDS(correlated double sampling),which can contribute to the fake hit rate of the sensor.

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Slope cut

s_i is the i-th sample if the pixel. The n in the formula is the calculation length of the slope. The slope cut used is 18 with n=150

noise is treated as the sum of RTS and noise background.

a slope cut is used to identify the RTS pixels

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efficiency of the RTS filter using a simulated RTS embedded in the noise

The efficiency of finding RTS depends on the RTS height. The efficiency will become lower as RTS height smaller.

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Fake hit rate

The fake hit rate of the sensor decreases as the threshold cut on the on the CDS signal is raised. If we require a fake hit rate 10^-6, the threshold is about 29 ADC count which is about 133 electron(RMS 6.1ADC corresponding to 28 electron)

plot is a section of the error function

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Number of RTS as a function of RTS height

• An RTS whose height is less than the CDS threshold can not produce a fake hit. So, we can ignore RT signals with a height that is below the CDS cut of 28 ADC counts.

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RTS effect on fake hit rate

Data set: 45k sample of 100k pixel

plot is a section of the error function

cut in electrons

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Summary

• For un-irradiated Mimostar3 sensor, the fake hit mainly comes from noise background. the fake hit comes from RTS less than 1 percent

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RTS pixel map

MS3 RTS pixel map

2.2% are RTS pixel (based on slope cut)

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Peaks from narrow low current periods

Fast rising time and normal descending time

rising time is about 10ms

The rapid rise region gives a negative CDS so it does not contribute fake hits, but there are probably an equal number with the opposite sign (see next slide) and we have to check that these have been properly counted.

Forward biased diode signal

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Ilow

high

Vdiode

Vdiode

I

low

high