A control unit, for controlling a threshold voltage of a circuit unit having transistor devices, includes a reference circuit and a measuring unit. The measuring unit is configured to measure a threshold voltage of at least one sensing transistor of the circuit unit, and to measure a threshold voltage of at least one reference transistor of the reference circuit. A differential voltage generator is configured to generate a differential voltage from outputs of the measuring unit and a bulk connection of the transistor devices in the circuit unit to which the differential voltage is fed as a biasing voltage.