Dark Current And Noise Measurements

To obtain dark current and noise data, an image sequence was performed following this scheme:

• 10 consecutive reset cycles of the whole detector

• Acquisition of 6 consecutive images

• Acquisition of 6 consecutive images

• Repeat wait & acquisition multiple times

• The data was processed and the results indicate that the mean dark current for the whole detector is around 0.12 e-/sec.

A remarkable effect was noticed. The initial pixels show a transient response after long periods of integration with output amplifier inactivity. Figure 2 shows the result of subtracting two consecutive frames obtained immediately after a long period of inactivity with the detector in dark conditions. This effect has been identified as a characteristic variation of the amplifier during temperature stabilization. The tests show that this phenomenon is observable after 20 seconds of detector inactivity. Once the thermal transient of the outputs of the detector has finished, a much more stable output is appreciated.

Figure 2. Transient effect due to thermal stabilization in the detector output stage.

The reset value depends on the previous saturation state of the detector. This is the case illustrated Fig. 3, showing the result of a persistency effect especially remarkable in one of the corners of the graph.

Figure 3. Persistency effect due to previous saturation.

A variation of the dark current versus time has been observed. Figure 4 illustrates the evolution of the dark current versus time. Different profiles correspond to different values of signal. The higher the charge before the reset, especially if the detector enters the saturation regime, the higher the initial dark current.

Figure 4. Dark current variation vs. time.

Figure 4. Dark current variation vs. time.

The dark files have been used to compute the detector noise. The mean readout noise value is 11 electrons.

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