The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect stellar occultation events generated by TNOs. TAOS II aims to monitor about 10000 stars simultaneously at 20Hz to generate a significant event rate. The TAOS II cameras are designed to cover the 1.7 degree diameter field of view of the 1.3m telescopes with a mosaic of ten 4.5k × 2k e2v CIS 113 CMOS sensors. The CIS 113 has a back-illuminated thinned structure to provide similar performance to that of back-thinned CCDs. The CIS 113 device has 16 micron pixels with 8 outputs, with a plate scale about 0.63”/pixel. With the freedom of direct row and column addressing, star boxes with sizes of 8 × 8 pixels in each sensor can be sampled at 20 Hz or higher with a pixel rate of 1M pixel/sec per channel. The sensors, mounted on a single Invar plate, are cooled to an operating temperature of about 200K by a cryogenic cooler. The gap between two sensors is about 0.5mm. The control electronics consist of an analog part and a Xilinx FPGA based digital circuit. One FPGA is needed to control and process the signal from each CIS 113 chip. Two large PCBs were used to fanout signals from the 10 CMOS devices through the vacuum chamber wall. A synchronization circuit receives a pulse from the control building to ensure the timing error of exposures of the three cameras is within 1 ms. The cameras were delivered and installed on the TAOS telescopes in 2023 and series of tests and adjustments have been carried out to optimize the performance. In this presentation, the camera performance in the full frame mode and the window mode will be detailed. The synchronization and the adjustment among the three cameras will also be presented.
The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect stellar occultation events generated by TransNeptunian objects (TNOs). TAOS II aims to monitor about 10000 stars simultaneously at 20Hz to generate a significant event rate. The TAOS II cameras are designed to cover the 1.7 degree diameter field of view of the 1.3m telescopes with a mosaic of ten 4.5k × 2k Teledyne e2v CIS 113 CMOS sensors. The CIS 113 has a back-illuminated thinned structure to provide similar performance to that of back-thinned CCDs. The CIS 113 device has 16 micron pixels with 8 outputs, with a plate scale about 0.63”/pixel. With the freedom of direct row and column addressing, star boxes with sizes of 8 × 8 pixels in each sensor can be sampled at 20 Hz or higher with a pixel rate of 1M pixel/sec per channel. The sensors, mounted on a single Invar plate, are cooled to an operating temperature of about 200K by a cryogenic cooler. The surfaces of the sensors were mounted to be within 30 microns to maintain a flat focal plane. The gap between two sensors is about 0.5mm. The control electronics consist of an analog part and a Xilinx FPGA based digital circuit. One FPGA controls and processes the signal from each CIS 113 chip. Two large PCBs were used to fanout signals from the 10 CMOS devices through the vacuum chamber wall. A synchronization circuit receives a pulse from the control center to ensure the timing accuracy of exposures of the three cameras is within 1 ms.
We report the testing results of the Teledyne e2v CIS 113 CMOS sensor at temperatures from room temperature down to 168K. The CIS 113 sensor is a customized device for the Transneptunian Automatic Occultation Survey (TAOS II) project. The sensor has 1920 × 4608, 16 μm pixels with 8 outputs. The pixels have a 5T design to provide anti-blooming capability with 18 μm thick high resistivity epitaxial silicon. The sensor provides two parallel and eight serial registers so the region of interests can be addressed and rapidly read out separately through different output channels. More than one thousand 8 × 8 star boxes can be sampled at a frame rate higher than 20 Hz. With a package similar to large format Teledyne e2v CCDs, the CIS 113 is three-side buttable. The device shows peak QE about 77% in 500-600 nm, readout noise around 3eand dark current lower than 2 e-/s/pix at -40 ℃. The linear full well for the device is higher at lower temperature and it is about 14400 e- at temperature lower than 210K. The device performance meets the science requirements with the operation temperature around 200K for TAOS II.
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