A programmable bias current compensation approach in current noise measurement applications

DC coupled transimpedance amplifiers based on operational amplifiers are common in the field of noise measurements on electron devices. The current required to bias the device under test typically flows through a resistor whose noise adds to the background noise of the amplifier with a contribution inversely proportional to the resistance value. The supply voltage of the circuit (typically a few volts) sets a limit to the maximum resistance for a given bias current and, hence, a minimum to the background noise that can be reached. To address this issue we propose to employ integrated solar cells to make available in the circuit voltages in the tens of volts range from which bias currents can be sourced with larger resistances leading to lower background noise. We propose the design and preliminary testing of such a system that is intended for applications in which bias currents are in the tens of nA range.