A precision spectrometer for measuring signals from the Epoch of Cosmological Recombination

Abstract

The rapid advances in processing capabilities of modern Field Programmable Gate Array (FPGAs) combined with high-speed analog-to-digital converters (ADC) make high-resolution, high dynamic range spectroscopy for verifying the signature of the Epoch of Recombination possible. A prototype 4 GHz precision spectrometer, based on quadrature sampling of analog signals followed by an efficient, parallelizable FFT architecture amenable to implementation inside an FPGA is described. Quadrature sampling of two analog signals, each having a bandwidth of about 2 GHz, is implemented using 10-bit, time-interleaved ADCs that has features for correction of gain, offset and phase mismatches. A combination of pipelined FFT IP-cores and a custom-designed parallel FFT engine provide 8192 spectral channels across each of the 2 GHz bands. Since the spectral purity of the sampling clock is an important consideration in precision applications, the effect of normally distributed jitter in the sampling clock on the deviations from a flat spectrum while sampling a band-limited white noise is presented.