A wideband ultra-low-current on-chip ammeter

A high-bandwidth ultra-low-current measurement circuit is presented in this paper. The circuit is capable of measuring an on-chip 75 fA current at a bandwidth up to 1 kHz with a noise floor of 0.235 fA_rms/√Hz. A low leakage reset scheme is utilized to improve the precision. Nested auto-zeroing combined with modified correlated double sampling is employed to mitigate the error due to various circuit imperfections. Noise analysis is carried out and “capacitive noise matching” is proposed to minimize the noise floor. The circuit is also capable of digitizing the measured current and streaming the data through a serial interface. The measurement circuit occupies 0.065 mm² of active silicon area in a 90 nm CMOS process and consumes 147 μW from 2.5 V and 1V supplies.