Multichannel current-mode spectroscopy amplifier in BiCMOS technology with selectable shaping time

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 of four elements. The fifth-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 intended 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-hold circuit. The four current outputs coming from the peak-hold circuits can be multiplexed on-chip to a single output pin. The noise performances are fully comparable with commercial instruments and the measured integral nonlinearity is below ±0.5%.