As a part of a design study for the On-Instrument Low Order Wave-front Sensor (OIWFS) for the TMT Infra-Red Imaging Spectrograph (IRIS), we recently evaluated the noise performance of a detector control system consisting of IUCAA SIDECAR DRIVE ELECRONICS CONTROLLER (ISDEC), SIDECAR ASIC and HAWAII-2RG (H2RG) MUX. To understand and improve the performance of this system to serve as a near infrared wavefront sensor, we implemented new read out modes like multiple regions of interest with differential multi-accumulate readout schemes for the HAWAII-2RG (H2RG) detector. In this system, the firmware running in SIDECAR ASIC programs the detector for ROI readout, reads the detector, processes the detector output and writes the digitized data into its internal memory. ISDEC reads the digitized data from ASIC, performs the differential multi-accumulate operations and then sends the processed data to a PC over a USB interface. A special loopback board was designed and used to measure and reduce the noise from SIDECAR ASIC DC biases2. We were able to reduce the mean r.m.s read noise of this system down to 1-2 e. for any arbitrary window frame of 4x4 size at frame rates below about 200 Hz.
In order to run the large format detector arrays and mosaics that are required by most astronomical instruments, readout electronic controllers are required which can process multiple CCD outputs simultaneously at high speeds and low noise levels. These CCD controllers need to be modular and configurable, should be able to run multiple detector types to cater to a wide variety of requirements. IUCAA Digital Sampler Array Controller (IDSAC), is a generic CCD Controller based on a fully scalable architecture which is adequately flexible and powerful enough to control a wide variety of detectors used in ground based astronomy. The controller has a modular backplane architecture that consists of Single Board Controller Cards (SBCs) and can control up to 5 CCDs (mosaic or independent). Each Single Board Controller (SBC) has all the resources to a run Single large format CCD having up to four outputs. All SBCs are identical and are easily interchangeable without needing any reconfiguration. A four channel video processor on each SBC can process up to four output CCDs with or without dummy outputs at 0.5 Megapixels/Sec/Channel with 16 bit resolution. Each SBC has a USB 2.0 interface which can be connected to a host computer via optional USB to Fibre converters. The SBC uses a reconfigurable hardware (FPGA) as a Master Controller. IDSAC offers Digital Correlated Double Sampling (DCDS) to eliminate thermal kTC noise. CDS performed in Digital domain (DCDS) has several advantages over its analog counterpart, such as - less electronics, faster readout and easier post processing. It is also flexible with sampling rate and pixel throughput while maintaining the core circuit topology intact. Noise characterization of the IDSAC CDS signal chain has been performed by analytical modelling and practical measurements. Various types of noise such as white, pink, power supply, bias etc. has been considered while creating an analytical noise model tool to predict noise of a controller system like IDSAC. Several tests are performed to measure the actual noise of IDSAC. The theoretical calculation matches very well with practical measurements within 10% accuracy.
Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a new multi-object Integral Field Spectrograph
(IFS) being designed and fabricated by the Inter-University Center for Astronomy and Astrophysics (IUCAA), Pune,
India, for the Cassegrain side port of the 3.6m Devasthal Optical Telescope, (DOT) being constructed by the Aryabhatta
Research Institute of Observational Sciences (ARIES), Nainital. It is mainly designed to study the physics and
kinematics of the ionized gas, star formation and H II regions in the nearby galaxies. It is a novel instrument in terms of
multi-IFU, built in deployment system, and high throughput. It consists of one magnifier, 16 integral field units (IFUs),
and 8 spectrographs. Each IFU is comprised of a microlens array and optical fibers and has 7.4” x 8.7” field of view with
144 spaxel elements, each sampling 0.8” hexagonal aperture. The IFUs can be distributed on the telescope side port over
an 8’ diameter focal plane by the deployment system. Optical fibers deliver light from the IFUs to the spectrographs.
Eight identical, all refractive, dedicated spectrographs will produce 2,304 R~1800 spectra over 370-740nm wavelength
range with a single exposure. Volume Phase Holographic gratings are chosen to make smaller optics and get high
throughput. The total throughput of the instrument including the telescope is predicted as 27.5% on average. Observing
techniques, data simulator and reduction software are also under development. Currently, conceptual and baseline design
review has been done. Some of the components have already been procured. The instrument is expected to see its first
light in 2016.