Traditionally, back-ends for radio telescopes have been built using a hardware-based approach with ASICs, FPGAs, etc. With advancements in processing power of CPUs, software-based systems have emerged as an alternative option, which has received additional impetus with the advent of GPU-based computing. We present here the design of a hybrid system combining the best of FPGAs, CPUs and GPUs, to implement a next generation back-end for the upgraded GMRT. This back-end can process 400 MHz bandwidth signals from 32 dual-polarized antennas, for both interferometry and beamformer applications, including narrowband spectral line modes for the interferometer, incoherent array and phased array mode of operations for the beamfomer, and also a voltage mode attached to a real-time coherent dedispersion system for the beamformer. We describe in detail the design and architecture of this system, including the novel features and capabilities. We also present sample results from the system that validate its performance in conjunction with the entire receiver chain of the upgraded GMRT.

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Direct Digital Synthesis is an improved method of producing analog waveforms where the generation is done completely in the digital sphere. In this paper, a design is presented for a Direct Digital Synthesizer (DDS) which generates multiple waveforms. The architecture is based on a 32 bit phase accumulator and a look-up table (LUT) as phase to amplitude converter. This design will be simulated in Xilinx. This DDS will offer qualities like fast switching, good frequency resolution and good stability. This DDS can become highly portable if it is designed on a Field Programmable Gate Array (FPGA).