In one example, this disclosure describes a circuit and techniques that may be used to measure the ion balance in an ionization balance device (10). The described circuit comprises a capacitor (22) that includes two conductors (23, 24), wherein a first one (23) of the conductors is exposed to the output of the ionization device, and the second one (24) of the conductors is shielded from the output of the ionization device. The first conductor may accumulate charge so as to quantify the output of the ionization balance device. A switch (29) may be used to discharge the first conductor at periodic intervals in order to measure the accumulated charge on the first conductor, and signal processing may be performed on this discharge measurement in order to generate feedback that can be used to control and adjust the output of an ion source.
