Comparative Analysis of Ultra-Low Current Measurement Topologies With Implementation in 130 nm Technology

Radiation detectors need front-end electronics capable of measuring currents over a large dynamic range with femtoampere sensitivity. The goal of this work is to find an alternative to the legacy systems implemented using discrete components or technology nodes of 350 nm or higher. The 130 nm technology is evaluated on its leakage current performance to assess its employability in such applications. A comparative analysis of three low current measurement topologies, namely the charge balancing, reset counting, and direct slope measurement methods, is carried out and their performance in different current ranges is evaluated. The charge balancing method was found to provide a better dynamic range with greater accuracy. However, in the lower current range, the direct slope measurement method was found to give faster results than the other two methods with comparable accuracy. Also, an application-specific integrated circuit implementing the charge balancing method was found to be linear throughout the dynamic range of -1 fA to -1 μA and could measure currents with an accuracy of ±7%. This achievement in the 130 nm technology opens the way to using the high-speed digital cells offered by this technology in conjunction with the low-leakage transistors to design a high-speed accurate current measurement system.