OLA, A LOW-NOISE BIPOLAR AMPLIFIER FOR THE READOUT OF SILICON DRIFT DETECTORS

A very low noise, 32-channel preamplifier/shaper chip has been designe d for the analogue readout of silicon detectors. The circuit has been optimised in view of the operation of Silicon Drift Detectors, which h ave very low capacitance and produce gaussian signals of sigma up to s imilar to 100 ns. The chip (OLA) has been designed and manufactured us ing the SHPi full-custom bipolar process by Tektronix. Each channel is composed by a preamplifier, a shaper and a symmetrical line driver, w hich allows to drive either a positive and a negative single ended out put separately on 50 Omega impedance or a differential twisted pair. T he intrinsic peaking time of the circuit is similar to 60 ns, and the noise is below 250 electrons at zero input load capacitance. The power consumption is 2 mW/channel, mostly due to the output driver.