DECTRIS Instant Retrigger technology
DECTRIS Instant Retrigger with adjustable dead time is a patented [EU, AU, CN (1224728), USA (4797363)] technology that enables non-paralyzable photon counting and achieves an improved high-rate counting performance. In a conventional single-photon counting X-ray detector, the charge pulses generated by impinging photons are counted by digital circuits. Pulses separated by less than the counting dead time pile up and as a result, photon counts can be lost. At high photon fluxes, pulse pile-up significantly affects the observed count rate and can lead to complete paralysis of the counting circuit. In PILATUS single-photon counting hybrid pixel X-ray detectors, count rate correction is applied to compensate for the counting loss at high count rates. However, counter paralysis limits the maximum usable count rate. In PILATUS3 detectors, DECTRIS Instant Retrigger technology re-evaluates the pulse signal after a predetermined dead time interval after each count and retriggers the counting circuit should pulse pile-up occur. The dead time interval is adjustable and is equivalent to the width of one single photon pulse. This results in non-paralyzable counting and allows for enhanced count rate correction to achieve improved data quality at high count rates.
Fig. 1 illustrates the principle of instant retrigger technology. The first diagram shows the signal pulses generated by impinging photons and the effective discriminator threshold level for single photon counting. The series of pulse signals shown comprises a single pulse, a pile-up of two pulses and a pile-up of multiple pulses. The second 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 counting X-ray detector, clearly illustrating that counts are lost in the case of pulse pile-up, and that this can lead to paralysis. The fourth diagram shows the respective dead-time generator output signal provided by a single photon counting X-ray detector with DECTRIS Instant Retrigger technology. Here, a predefined dead time interval is started whenever a count has been registered. The fifth diagram shows the corresponding counts being registered, including potential retriggering of the counting circuit after the dead-time interval after each count. Pulses are counted more accurately in the case of pile-up, and counting is non-paralyzable.
Improved High-Rate Counting Performance
PILATUS3 X-ray detectors achieve improved high-rate counting performance compared to previous PILATUS X-ray detectors thanks to various enhancements of the CMOS readout ASIC. These include DECTRIS Instant Retrigger technology to achieve non-paralyzable counting, which is fundamental for enhanced high-rate counting performance. In addition, counter overflow handling makes it possible to unambiguously determine the incoming photon rate. Improved pixel uniformity is provided to obtain enhanced count rate homogeneity over entire modules. In the new design, crosstalk is reduced, which yields better stability and enables higher local and global count rates.
Fig. 2 shows the typical count rate characteristics of PILATUS3 X-ray detectors with DECTRIS Instant Retrigger technology compared to previous PILATUS X-ray detectors. PILATUS3 features significantly enhanced count rate capabilities. In PILATUS3 detectors, count rate correction can be applied more accurately, thus resulting in better data quality up to rates of more than 107 photons per second in a single pixel. The new design shows no limitation of the global count rate and can handle global rates of more than 3*108 photons per second and mm2.
Reduced Readout Time
PILATUS3 X-ray detectors feature a reduced readout time of less than 1 ms and achieve increased frame rates of 100 to 500 Hz.