A compact low-noise broadband digital picoammeter architecture

A low-noise (⩽4 fA/√Hz), broadband (⩾100 kHz) compact architecture and related operation solutions are proposed for portable and low-cost time-domain acquisition of currents with effective resolution in the order of 1 pA and below. The front-end architecture is based on an integrating-differentiating scheme to achieve the optimal performance in terms of input-referred equivalent noise, but it overcomes the typical noise/bandwidth trade-off by making the sampling frequency of the A/D conversion independent from the rate at which the analog front-end is reset. In order to strongly mitigate the main drawback, i.e., the introduction in the system of an inherent time-variance, a Track-and-Hold circuit synchronized with the reset is exploited. For validation purposes, a dual-channel prototype was implemented in a low-cost CMOS technology. The prototype is characterized by standard figures of merit and is experimentally validated by two simple case studies, which are typical of practical applications.