Performance of a low noise front-end ASIC for Si/CdTe detectors in Compton gamma-ray telescope

Compton telescopes based on semiconductor technologies are being developed to explore the gamma-ray universe in an energy band 0.1-20 MeV, which is not well covered by the present or near-future gamma-ray telescopes. The key feature of such Compton telescopes is the high energy resolution that is crucial for high angular resolution and high background rejection capability. The energy resolution around 1 keV is required to approach physical limit of the angular resolution due to Doppler broadening. We have developed a low noise front-end ASIC (application-specific integrated circuit), VA32TA, to realize this goal for the readout of double-sided silicon strip detector (DSSD) and cadmium telluride (CdTe) pixel detector which are essential elements of the semiconductor Compton telescope. We report on the design and test results of the VA32TA. We have reached an energy resolution of 1.3 keV [full-width at half-maximum (FWHM)] for 60 and 122 keV at 0° C with a DSSD and 1.7 keV (FWHM) with a CdTe detector.