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 mm2 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.
Highlights
I ONISATION chambers are some of the most used devices for radiation monitoring in the many fields spanning nuclear industry, high energy physics experiments, radiation therapy, etc. [1]–[3]
At the European Organization for Nuclear Research (CERN), different kinds of Ionisation chambers are used to address the complex nature of radiation fields present at various experimental facilities [4], [5]
In the current radiation monitoring system at CERN, the front-end electronics is implemented with discrete components and performs current-to-frequency conversion (CFC) using a reset counting method
Summary
I ONISATION chambers are some of the most used devices for radiation monitoring in the many fields spanning nuclear industry, high energy physics experiments, radiation therapy, etc. [1]–[3]. At the European Organization for Nuclear Research (CERN), different kinds of Ionisation chambers are used to address the complex nature of radiation fields present at various experimental facilities [4], [5]. In the current radiation monitoring system at CERN, the front-end electronics is implemented with discrete components and performs current-to-frequency conversion (CFC) using a reset counting method This system, described in [6] and [7], is capable of measuring the current produced by the ionisation chamber from 1 fA to 2 μA. A new version of the ASIC was developed based on the results obtained in [13] and taking advantage of the high-speed core transistors to build a true single-chip solution that deals with current measurement, digitization, data processing, and communication. Generated Current γ : 80fA → 800nA γ : 5.7fA → 56nA n: 2fA → 20nA γ : 12fA → 250nA
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