The high resolution versatile digital spectrometer of HIFI-HSO

We present a versatile digital autocorrelation spectrometer designed to suit the needs of HIFI, the sub-millimeter heterodyne instrument of the ESAs HSO satellite. This spectrometer will offer a set of four observing modes with different "on-line resolution/total bandwidth" combinations. An original architecture, based on mixed gallium arsenide and silicon technologies, allowed us to realize a 512 channel, low-power consumption and high speed correlation module. We give some details on the optimization of the design (quantization scheme, readout format) performed to fit the HSO-HIFI requirements. We also describe an approach to distortion correction which takes into account the non-rigorous adjustment of the comparison thresholds of the spectrometer's analog to digital converter. Up to now, the efficiency of a spectrometer has been described as depending only on the quantization scheme used. In this paper, we show that the efficiency varies within the spectrum and we introduce the "spectral efficiency", which is connected to the input signal band shape. (C) 2003 Elsevier B.V. All rights reserved.