Signal processing instrumentation of gamma-ray telescopes of the GRACE project

Abstract

The TACTIC Cerenkov telescope has recently been commissioned at Mount Abu, Rajasthan. The signal processing electrinics of the 349 element imaging camera was a totally indigenous development. A number of groups from Electronics Division and NRL, BARC participated in the development of the various subsystems of the imaging camera which included multichannel detector bias supply, fast amplifter, charge to digital converter, 50 MHz scaler, programmable trigger generator and data acquisition electronics. Most of the multichannel electronic modules followed either the NIM or the CAMAC standard. A considerable amount of interconnection cabling was necessary. In the second phase of GRACE project two further telescopes, namely MACE and MYSTIQUE have been proposed, each having a considerably larger number of channels. Implementation of these projects with the existing type of instrumentation would pose formidable problems of interconnection, testing and maintenance. A new type of integrated module has therefore been proposed. Each of these modules would provide sixteen channels of pulse processing electronics, first level trigger generation and an onboard data acquisition and communication processor. These processors would be networked by ethernet interface. Similarly, detector bias would be generated with sixteen channel HV modules with onboard processors, which would also be networked with a slower link. This type of high density pulse processing electronics would significantly reduced the interconnection and maintenance problems. However the required high density electronics is achievable only with extensive use of hybrids and ASICS. Work has been initiated for fabrication of fast amplifiers in hybrid form. Similarly, multichannel scalers and constant fraction discriminators would be implemented in ASIC.