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 30 nA. Current noise density reaches a value of 500 ??A/??Hz, equivalent to a 100 G?? resistor, giving a 1 pA_RMS noise in a 100 kHz band. The strictly equal operating point of all transistors ensures excellent linearity even at femtoAmpere input current.