Analog front-end cell designed in a commercial 0.25 μm process for the ATLAS pixel detector at LHC

A new analog pixel front-end cell has been developed for the ATLAS detector at the future Large Hadron Collider (LHC) at the European Laboratory for Particle Physics (CERN). This analog cell has been submitted in two commercial 0.25 μm CMOS processes (in an analog test chip format), using special layout techniques for radiation hardness purposes. It is composed of two cascaded amplifiers followed by a fast discriminator featuring a detection threshold within the range of 1000 to 10000 electrons. The first preamplifier has the principal role of providing a large bandwidth, low input impedance, and fast rise time in order to enhance the time-walk and crosstalk performance, whereas the second fully differential amplifier is aimed at delivering a sufficiently high-voltage gain for optimum comparison. A new do feedback concept renders the cell tolerant of sensor leakage current up to 300 nA and provides monitoring of this current. Two 5-bit digital-to-analog converters tolerant to single-event upset have been implemented for threshold and recovery-time pixel-to-pixel matching purposes. Special attention has been paid to the power-supply rejection ratio to minimize sensitivity to pickup. The complete cell dissipates 30 μW, occupies an area of 50×90 μm² and is operated with a single 1.6-V power supply. Measurements of two test chips are presented.