Theoretical analysis and experimental characterization of a novel VLSI current-mode shaping cell for high-resolution spectroscopy

We propose a novel VLSI current-mode shaping cell for high-resolution spectroscopy. This innovative topology is based on the possibility of virtually increasing the physical value of an integrated resistor thus allowing to design shaping amplifiers with high-value (∼1-10 μs) time constants with reduced area occupancy. In this paper, we present the main issues of the circuit design and a detailed analysis of the noise performance of the proposed topology. Profiting from this current-mode approach, we have designed in 0.8-μm BiCMOS technology a fifth-order shaping amplifier (0.5-μs shaping time) to be coupled to monolithic arrays of silicon drift detectors (SDDs) for high-resolution X-ray spectroscopy. The measured integral-non-linearity is below ±0.2% and the achieved energy resolution at the Mn Kα line (measured with the proposed shaping amplifier coupled to a single-channel 5 mm² Peltier-cooled SDD) is 159 eV FWHM fully comparable to the one obtained with a commercial shaping amplifier with the same time constant.