OLA, a low-noise bipolar amplifier for the readout of silicon drift detectors

A very low noise, 32-channel preamplifier/shaper chip has been designed for the analogue readout of silicon detectors. The circuit has been optimised in view of the operation of Silicon Drift Detectors, which have very low capacitance and produce gaussian signals of sigma up to similar to 100 ns. The chip (OLA) has been designed and manufactured using the SHPi full-custom bipolar process by Tektronix. Each channel is composed by a preamplifier, a shaper and a symmetrical line driver, which allows to drive either a positive and a negative single ended output separately on 50 Omega impedance or a differential twisted pair. The 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.