One of the hallmarks of EIGER ASIC is its continuous readout that enables kilohertz frame rates with duty cycles greater than 99%. Every pixel of an EIGER ASIC features a digital counter for noise-free counting of the observed photons. A readout buffer accompanies this digital counter in each pixel. After frame acquisition, the state of the counter is transferred to the readout buffer virtually instantly. A subsequent frame can start after only 3 microseconds, while the previous frame is being read out from the readout buffer. The continuous readout of EIGER with counter and buffer in every pixel maximizes duty-cycle and data collection efficiency without requiring a rolling shutter.
EIGER’s auto-summation mode is an additional benefit of continuous readout with high duty cycles. While a single frame is limited to the 12 bits of the digital counter, auto-summation extends the data depth up to 32 bits or more than 4.2 billion counts per pixel, depending on the image’s number of summed frames. At short exposure times and frame rates in the kilohertz range, all counts are captured in the pixel’s digital counter and directly read out as an image. If long exposure times are requested, frames are still acquired at high rates on the pixel level; effectively avoiding any overflows. The detector system sums the frames to images on the fly; extending the bit depth of the data by the number of summed frames. EIGER’s auto-summation mode maintains a duty cycle greater than 99% at all times due to continuous readout with 3 µs dead time.