Summary 500 words
The upgrade plans for the Large Hadron Collider (LHC) at CERN foresee an increase of the peak luminosity by a factor of up to 5 beyond the nominal value of 10^34 cm-2 s-1. The corresponding hit rates in the Monitored Drift Tube (MDT) chambers of the ATLAS muon spectrometer, mainly due to converted gammas and neutrons produced in the particle interactions in the detector, will lead to data rates in excess of the presently available readout bandwidth and to higher radiation damage, calling for at least partial replacement of the MDT readout electronics. For the front-end Amplifier-Shaper-Discriminator chip (ASD) we selected the IBM 130 nm CMOS 8RF-DM technology because of its accessibility via CERN and also in view of possible synergy with the front-end chip development for other ATLAS and LHC detector upgrade projects.
Each channel of the ASD chip contains a preamplifier, a three-stage shaper and a discriminator with lvds-output. One of the channels has an analogue output to monitor the pulse shape before the discriminator stage. In addition, a Wilkinson ADC for each channel, a DAC for programmable on-chip threshold generation, on-chip test pulse circuitry and JTAG controls have been implemented. As the pulse height is proportional to the supply voltage, on-chip LDO voltage regulation is used.
The chip is mounted on a 2-layer PCB and connected to an input protective network of identical design to the present system. In the chip layout, the low-resistive E1 and L1 layers of the 8RF-DM architecture were used for optimum on-chip grounding and supply voltage distribution.
Test pulse measurements showed very good agreement with the performance of the existing ASD chip as well as with the simulation. Gain uniformity between the channels of each chip and between different chips is within 2 %, cross-talk below 1.5 %. Noise corresponds to 6000 electrons (RMS) at 10 pF external capacitance, typical for the MDT readout. All measurements were done at the nominal supply voltage of 3.3 V, resulting in a power consumption of 24 mW per channel.
A first neutron irradiation test showed very little degradation of the ASD performance parameters as expected.