Dectris EIGER 2 - 8-Bit Readout

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Figure 3.1: Signal Waveforms Illustrating the DECTRIS INSTANT RETRIGGER

technology

The Instant Retrigger principle is illustrated in gure 3.1. The rst diagram shows the signal pulses generated

by impinging photons and the eective discriminator threshold level for single photon counting. The pulse

signal includes a series of one single pulse, a pile-up of two pulses and a pile-up of multiple pulses. The sec-

ond diagram shows the corresponding digital discriminator output signal that triggers the counting circuit.

The third diagram shows the corresponding counts being registered by a conventional single photon count-

ing X-ray detector, clearly illustrating that counts are lost in the case of pulse pile-up and that this can lead

to paralyzation. The fourth diagram shows the respective dead-time generator output signal provided by a

single photon counting X-ray detector with Instant Retrigger. Here, a predened dead time interval is started

whenever a count has been registered. The fth diagram shows the corresponding counts being registered,

including potential retriggering of the counting circuit after the dead-time interval after each count. This clearly

illustrates that pulses are counted more accurately in the case of pile-up and that counting is non-paralyzable.

3.2.5. 8-bit Readout

Information #1

The 8-bit readout mode is only available with DECTRIS EIGER

2 X and XE detectors.

The EIGER2 ASIC allows the option to read out only the rst 8 bits of every counter instead of the full 16

bits. This enables a higher maximum frame rate at the cost of a lower dynamic range. The 8-bit mode is

automatically enabled as soon as the frame rate exceeds the maximum frame rate in 16-bit mode, as indicated

in the Technical Specications.

When using the 8-bit mode, it is important not to exceed the maximum ux per pixel, as there is no overow

protection and the counter will roll over if 255 counts are exceeded. This means the maximum ux per pixel

is 255 × frame rate in 8-bit mode.

DECTRIS EIGER

2 User Manual v1.8.2 6 | 36