Charge-balancing current integrator with large dynamic range

A simple circuit based on the popular 3140 amplifier has a sensitivity of 10 pC/count and a useful input current range from 1 pA to 10 μA. Apart from an input leakage current of the order of 0.1 pA, the circuit is linear and stable to approximately 0.1%. During overload, pulses are issued at a maximum rate and for sufficiently brief overloads the error in integrated current remains small. The circuit is easily converted from one input polarity to the other. (orig.)