An Ultra Low Current Measurement Mixed-Signal ASIC for Radiation Monitoring Using Ionisation Chambers

Abstract

Measurement of total ionizing dose in a radiation field is efficiently carried out by ionisation chambers. The paper details the design of a mixed-signal ASIC for the front-end electronics of ionisation chambers. A single chip solution for ultra-low current measurement is designed by combining the current processing analog section realized using low leakage thick gate transistors and the data handling digital section implemented using fast thin gate transistors. The design succeeds in limiting the cross coupling between the two circuit domains using deep nwells and guard rings. The ASIC fabricated in 130 nm technology attains a wide dynamic range of -7 fA to -20 µA with maximum error in measurement less than ±4 %. The ASIC occupies an area of 3.52 mm 2 and has a total power consumption of 17.4 mW. The femtoampere range input leakage current of the ASIC contributed primarily by the ESD diodes was found to be varying exponentially with temperature. Dose rate measurements from 5 µSv/h to 7.4 Sv/h is demonstrated by interfacing the ASIC to an ionisation chamber.

30 Years of Electronics Evolution for CERN Safety Radiation Monitoring

“…The latest version of ACCURATE 2 is an evolution over ACCURATE 1 using the same technology. ACCURATE 2 exists in two flavours -the analog-only ACCURATE 2A and mixed signal version ACCURATE 2M [8]. The ASIC implements current measurement using the direct slope method and charge balancing.…”

Multiequipment Radiation Measurements in a Field Generated by Bombarding a 1-GeV/u Fe Beam on a Polyethylene Target at GSI and Comparison to FLUKA Simulations

“…They are typically installed at CERN [11] close to the accelerator and experiment components and are exposed to strong radiation fields during operation. They are made of graphite and plastic to minimize the activation of materials of the chamber itself [12]. The operational principle of this detector is similar to pressurised ionisation chambers.…”

“…The ASIC output could thus be quantified as charges or the average current in a predefined time interval. In-depth details of the ASIC could be found in [18]. In the current experiment, both the charge output and current converted into dose rate are used in comparisons.…”