Ultra-low-noise CMOS current preamplifier from DC to 1 MHz

An ultra-low-noise, DC–1 MHz, current preamplifier is presented featuring a matched double-MOS architecture around a low offset opamp to obtain bidirectional gain with a signal range from −40 to 30nA. Current noise density reaches a value of 500aA/√Hz, equivalent to a 100GΩ resistor, giving a 1pARMS noise in a 100 kHz band. The strictly equal operating point of all transistors ensures excellent linearity even at femtoAmpere input current.