A four-channel ADC on a VME board

A four-channel analog-to-digital converter (ADC) for data acquisition in nuclear physics experiments has been developed on a VME board. The circuit architecture is a multistretcher configuration based on a fast conversion module. The board can operate either in sampling or in autotrigger mode with an input range of 4.096 or 8.192 V; the risetime protection can vary from 1 to 32 mu s. Many functions are software selectable; the most significant are: the linear gate trigger mode, the risetime protection, and the ability to set of the low and high thresholds independently for each channel. The conversion module is based on a two-step concept: an overall resolution of 12 b, with a conversion time lower than 1 mu s, is obtained by means of two 8-b flash ADCs and a sliding-scale compensation technique is used to improve the differential linearity. The differential linearity error is less than 1%, while the integral linearity error is 0.023% over the 98% of the dynamic range.