Each SPAD is biased and driven by appropriate detection and control electronics. The core of the detection electronics are the integrated Active-Quenching Circuits (iAQC), one for each SPAD. Each iAQC is able to bias the corresponding SPAD above the breakdown voltage, generate a digital pulse each time a photon is detected and quickly quench the SPAD (by lowering its bias below breakdown). At the end of the cycle, the SPAD is ready to detect a new photon. Figure 4 shows the block diagram of each iAQC. The iAQCs are packaged with a possible five on one chip.
The entire detection board provides not only the 12 chips containing a total of 60 iAQCs , but also 15 quad output drivers that output 60 differential lines through two SCSI connectors (requested by ESO for backward compatibility with the existing MACAO systems).
Moreover, an 8-bit micro-controller manages all settings, diagnostics, and signal communication. Commands and telemetry (temperature, over voltage, hold-off duration) will be transferred through an USB interface. Figure 5 shows the block diagram of the detection board.
Was this article helpful?