Space targets are mainly divided into spacecraft and space debris working in orbit. Important near-Earth objects can be accurately detected and tracked, and their threats to the planet security can be predicted by monitoring their orbit and volume parameters. Optical telescope is one of the most important astronomical telescopes, science-grade image sensors were used to collects optical information about stars. In modern times, with the rapid development of semiconductor technology, CMOS (Complementary Metal Oxide Semiconductor) image sensor has high data transmission rate and high integration, CMOS image sensors have become the main optical imaging image sensors used in astronomical telescopes. In this presentation, the imaging principle and firmware design of a scientific CMOS camera named PX400 are introduced and tested. The PX400 uses a scientific image sensor called GSENSE400BSI (hereinafter referred to as GS400) produced by GPIXEL, which has a high data readout rate and a variety of operating modes.
The conventional response band of Indium Gallium Arsenide (InGaAs) detectors ranges from 0.9 to 1.7μm. The J atmospheric window (1.25μm) in infrared astronomy falls at the center of the response band of InGaAs detectors, making them widely used in this spectral region for infrared astronomy. Three representative Chinese-made Indium Gallium Arsenide focal plane arrays (InGaAs FPAs) were selected, and corresponding interface circuits were designed to match the testing system. Key performance indicators such as dark current, gain, and readout noise were tested.
In order to enhance the observational ability in infrared wavelength, a K-band MCT(Hg-Cd-Te) mosaic camera is constructed for a near-infrared telescope. In this paper methods of low temperature control and vibration measurement of the infrared camera are introduced. In order to suppress the dark current of the MCT detector of the camera, the detector is refrigerated to below 80K using a tube cryocooler in a vacuum chamber. To suppress the scatter light from lens of optics, the lens in front of the detectors should be cooled to below 150K. And in order to avoid damage of the cold optical lens caused by low temperature, two-stage temperature control is carried out on the base-plate of detectors and cold optics. Furthermore, the running cryocooler will cause small vibration of the detector, which will reduce the imaging quality of the camera. An anti-vibration method is designed to reduce the influence of the vibration. A three-axis vibration measurement of the detector is introduced, which provides data basis for the analysis of the influence of vibration on imaging and image correction.
Chinese scientists plan to build an 80 centimeter caliber near-infrared astronomical telescope in Antarctica, consisting of one telescope and two terminal devices. The K-band astronomical imaging system is one of the main terminals. We designed and characterized a 1x3 K-band near-infrared mosaic camera and the MCT detectors form Shanghai Institute of Technical Physics. The single pixel array of this camera is 640x512, with a single pixel size of 15 μm. Three detectors arranged in a mosaic configuration generated a focal plane pixel array of 1920x512. To ensure the optimal performance of the K-band astronomical imaging system, we used Dewar sealing, vacuum maintenance, and thermoacoustic refrigerator to cool the detector to 80K and the optical lens and components to 150K. In addition, a low-noise power supply design and electronic devices with low readout noise are adopted to ensure the minimum dark current and low readout noise of the mosaic infrared camera. The flatness of the mosaic detector is less than 20 μm . Complies with the design specifications for K-band astronomical imaging system.
Scientific grade Charge Coupled Device(CCD) is widely used in astronomical telescope as imaging sensor at present. A CCD camera based on CCD driving and readout ASIC is designed using CCD47-20 in this paper. The CCD driving and readout ASIC chips include CCD drive chip BCDA2(Second Edition Bias Clock Driver ASIC) and CVRA2(Second Edition CCD Video Readout ASIC). BCDA2 provides multichannel clock and bias voltage for CCD. CVRA2 processes the output signal of CCD by correlated double sampling double slope integral. The processed signals will be sampled by external ADC. Based on the BCDA2 and CVRA2, the electronics system of the camera is designed including a Connecting Board, a pre-amp board and a master control board with CCD driver and CCD readout. The test result shows it’s working well.
With the increase of human activities in space, a large number of space artifacts have been generated around the Earth which called Near Earth Objects (NEO), most of which are space debris. CMOS image sensor can achieve very high frame rate by electronical shutter and suitable for NEO observation with its fast moving. For space objects observation, key technologies of a large-format and high-rate scientific CMOS camera were studied, including low-noise readout and low-interference refrigeration technology, real-time processing algorithm, high-speed data transmission technology, system integration technology and high precision timing technology , etc. A 4K*4K pixel scientific CMOS camera is introduced in this paper with 24fps rate in full frame mode and high timing accuracy of exposure synchronization with 10ns, which has great advantages for the initial orbit positioning of the space objects. The overall size of the camera is 143mm * 160mm * 168mm. The readout noise of the camera is about 4.4e-. At present, the camera has been installed and running at Xinglong Observatory.
The Wide Field Survey Telescope (WFST) is being developed by University of Science and Technology of China and Purple Mountain Observatory. The camera of WFST is proposed to image with a mosaic Charge-coupled devices (CCD) array, which consists of 9 CCD290-99 detectors. It has requirements of decreasing the size and reducing total power dissipation for electronics system. Considering the demands of CCD290-99, two chips Application-specified Integrated Circuits (ASIC) were designed, called Second Version of Bias-Clock-Driver ASIC (BCDA2) and Second Version of CCDVideo- Readout ASIC(CVRA2) respectively. These chips have been upgraded and optimized based on the BCDA and CVRA. BCDA2 provides multi-channel clocks and biases to drive CCD290-99 and CVRA2 is used for the readout circuits of CCD signal processing. BCDA2 integrates 5 channels low noise biases with adjustable voltage and 9 channels low power dissipation clocks with adjustable driving capability. CVRA2 integrates 4 channels low noise readout circuits. Serial Peripheral Interface (SPI) was designed for configuration of BCDA2. BCDA2 and CVRA2 were designed with the Global Foundries 180 nm BCDlite technology. The area of bare chip is 3.1mm × 6mm.
The infrared astronomy is a very important branch of astronomy. Imaging observation is the basic approach to conduct infrared astronomy observation. Therefore, infrared Focus Plane Array (FPA) detector is needed for an infrared telescope. Detection toward celestial body need the detector to have high performance like extremely low dark current and low readout noise. Therefore, we designed a test equipment based on a 640 × 512 InGaAs array detector with a cryocooler which can cool the detector down to 77K. The detector is InGaAs of SITP-Hu-I type which is sensitive to 0.9us ~ 1.7um band. The test equipment is composed of a vacuum cryocooling system, a mechanical system and an electronical system. The vacuum cryocooling system can provide a low-temperature vacuum environment for the detector, and the mechanical system provides firm supporting. The electronic system provides the driver and readout of the detector.
In order to implement the driver and readout functions for several types of scientific CCD detector, meanwhile decreasing the size of electronics and reducing the total power dissipation for a large scale mosaic CCD detector system, two Application-specified Integrated Circuits (ASIC) were designed. One is for CCD driver and called BCDA (Bias Clock Driver ASIC), which is to provide multi-channel clocks and Bias voltage; the other is for CCD video processing and called CVRA (CCD Video Readout ASIC). In the BCDA chip, the bias drivers are generated by high voltage amplifiers. The clock drivers are made of a clock switch circuit and high voltage amplifier. Two 8-bit current-steering DACs are used to adjust the driver capability and high-level voltage of clocks. The CVRA chip processes the video signal of a CCD detector. The functions of CVRA chip consist of pre-amplifier, single-to-differential circuit, CDS circuit, and integrating circuit. The Global Foundry 180 nm BCDlite technology is used in this chip design. The first round of design has been finished and part of tests of two chips have been done.
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