The Beam Losses Monitor (BLM) system measures the radiation levels around the LHC in order to protect its components and prevent the quenching of magnets. The system, designed and constructed by CERN's BE-BI group, contains approximately 4000 gas filled ionization chambers (IC) installed throughout the accelerator that produce an output current proportional to the radiation losses. EP-ESE is collaborating with BE-BI on a project to develop a radiation tolerant version of the acquisition module in view of the high luminosity upgrade; to this end two versions of a current-digitizing ASIC have been designed in 130nm CMOS technology. The main challenges of the project are the signal dynamic range of 180dB (from 1pA to 1mA) and the compatibility with a maximum input capacitance of 5nF.

One of the chips is based on a reference-less self-timed current to frequency converter (CFC), as shown below:


The other chip is based on continuous Sigma-Delta modulation, as shown below:



The noise affecting the measurement can be effectively filtered by extending the acquisition window and performing a numerical averaging. Both ASICs reached the sub-pA resolution within a few seconds of sample acquisition.

The two chips use the same layout architecture and share the design of the main blocks (digital part, pad ring, integrator bias distribution). One of the chips is shown in the photo below.