Transimpedance amplifier for very high sensitivity current detection over 5MHz bandwidth

The paper presents a transimpedance amplifier made on standard 0.35 mum CMOS technology specifically conceived to measure the impedance of low-conductivity nano-bio devices. The circuit combines a bandwidth of 5 MHz with an extremely low noise of 3 fA/sqrt (Hz) by using an integrator-differentiator scheme. An innovative feedback network continuously discharges the integrator capacitance to ensure an unlimited measuring time irrespective of the do input current up to 20 nA. An highly linear 300 GOmega active resistance, used in the feedback network to extend the lower limit of the bandwidth down to 100 Hz, will be also described.