Four-channel current-mode VLSI shaping amplifier with selectable time constant for high resolution X-ray spectroscopy

A four-channel shaping amplifier for high resolution spectroscopy has been designed and realized in 0.8 μm BiCMOS technology to process the signals coming from a new state of the art silicon drift detector composed by four elements. The 5th-order semi-Gaussian shaping function is obtained by means of a novel current mode topology based on current mirrors to amplify the time constants and on a current feedback technique to obtain complex conjugate poles. The proposed shaper allows the user to choose among four possible gains and two possible shaping-times. The slow shaping time (500 ns) is for best energy resolution measurements while the short one (167 ns) allows high rate measurements. The maximum dynamics for the input signal, coming from any kind of preamplifier, is 400 mV. The output signal can be taken both as a voltage and as a current. We have provided each channel with both a voltage-mode and a current-mode peak stretcher. The four stretched current outputs can be multiplexed on-chip to a single output pin. The noise performances are fully comparable with commercial instruments and the measured linearity is below ±0.5%.