Temperature sensitivity of the AMS RICH front end chip

The aim of the present study was to quantify the effect of the temperature on the electronic response of the chip, specially about a possible drift of the pedestal amplitude with temperature. The tests have been carried out the latest chip version, i.e., without external current converter. The chip has been tested with the PMT test bench associated to a temperature monitored chamber, and measurements have been performed between -30 deg. C and 50 deg. C. The observed drift due to the temperature of the average pedestal was about one channel per degree for gain five. To improve this drift, we added a diode on the pedestal level input of the chip. The diode brought a sensibility of - 2 mV per degree in the pedestal level input, resulting in a correction of - 0.39 channel per degree on the average. This study was necessary to quantify the effect of the temperature on the electronic response. The use of a diode improved the sensibility of the pedestal shifting between -30 deg. C and 50 deg. C corresponding to 0.76% of the single photo-electron. In this way, the calibration of the detector will not be dependent on the temperature. However, the uncorrected effect was small and with minor contribution to the drift spreading, 0.78 channel over the expected range of temperature, compared to the pedestal sigma which is of the order of 4 channels, and the modification may not be necessary. So we plan to implement the correction in the microcircuit electronics front end