An RF circuit comprises a charge pump configured to generate current pulses having a first current amplitude and a predetermined duration; and a capacitive element configured to receive the current pulses and to generate a tuning voltage depending thereon. An RF oscillator is configured to generate an RF signal having a frequency that is dependent on the tuning voltage. The RF circuit comprises a measuring circuit configured to generate a measurement signal representing the tuning voltage or the frequency of the RF signal. A controller circuit is configured to drive the charge pump in order to change the first amplitude of a current pulse by a current difference, and ascertain a first change in the measurement signal and a second change in the measurement signal. A measurement value for the first amplitude can be calculated based on the first change and the second change based on the current difference.