Nucam: a 128 Channel Integrated Circuit with Pulse-Height and Rise-Time Measurement on Each Channel Including on-Chip 12bit ADC for High-Z X-Ray Detectors

The Nucam chip is a 128 channel low-noise application specific integrated circuit primarily intended for readout of CZT and CdTe detectors. The data driven ASIC channels recognise signals above threshold and store the analogue levels in peak-hold circuits. Signals from all peak-holds are routed to a single 1 MHz through-put 12-bit ADC. The digital result of this is output together with the channel number and a 6-bit collection-time estimate for the signal. The collection-time is estimated by differentiating the signal and clocking a counter during the time over zero. This collection-time gives an estimate of the hole contribution to the predominantly electron signal in thick semiconductor detectors. This can then be used in an off-line correction for charge carrier trapping and ballistic deficit. We explain the architecture and specification of the ASIC and measurements carried out to assess the operation and performance of the circuits. We show initial results with a CZT detector and the modifications that are being made to the ASIC to optimise it for future applications.