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An opto-coupling circuit based on the Siemens IL300 linear optocoupler and the methods to assess its static and dynamic performances are presented. It is shown that IL300, due to its built-in linearizing feedback photodiode, makes it possible to build coupling schemes that associate good linearity with the inherent properties of optical devices, as true galvanic isolation, high isolation voltage and transmission down to DC. The integral linearity, 0.029%, obtained on the coupling of typical nuclear spectroscopy pulses makes us believe that traditional capacitive coupling used in nuclear spectroscopy circuits can be replaced by optical coupling in the near future.

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. >

A new type of ADC is being developed to satisfy the requirements of the HEAO high spectral resolution gamma ray spectrometer. This 13 bit design utilizes a double successive approximation technique that overcomes the usual differential linearity problem. Stability of a few ppm/°C, differential linearity of 2% and integral linearity of 0.05% have been demonstrated.