An 8 channel GaAs IC front-end discriminator for RPC detectors

Although not traditionally considered for particle detector readout, circuit solutions based upon GaAs IC technologies can offer considerable performance advantages in high speed detector signal processing: high fT devices, such as the GaAs MESFET, allow the realization of front-end tuned amplifiers and comparators with the same detector time resolution. Such a feature is well-suited for RPC particle detectors, characterized by short pulse duration and constant shaping responses. A new design procedure shows the suitability of high speed narrow band GaAs amplifiers as voltage-sensitive input stages of front-end discriminators to perform the required voltage amplification for the following comparator, ensuring, at the same time, SNR optimisation, high gain and low power consumption. As an application of the proposed approach, a full-custom analog chip has been designed and realized using 0.6 μm GaAs MESFET technology from Triquint foundry. Eight channels of a front-end discriminator composed of a tuned voltage preamplifier followed by a high speed comparator have been realized with a resulting die size of 1.5×2.3 mm2. The chip turns out to be very stable, featuring high voltage gain (>1000), high gain-bandwidth product (1011) and low sensitivity (∼50 μV), fast rise time (1.5 ns) and a power consumption of 25 mW per channel. It has been successfully tested as front-end stage in RPC trigger detectors.