An arrangement having a device for providing high-frequency voltage UApp for contact coagulation of the biological tissue. The device is equipped to operate with a high voltage that is normally not suitable for contact coagulation, but otherwise used for spark coagulation, for example, more than 400V at the beginning of the contact coagulation. During the operation of the generator the tissue impedance Z is monitored. This can occur by means of continuously measuring the voltage UApp of the flowing current IApp and the phasing φ between the voltage and the flowing current. Using both, the measuring unit continuously determines the tissue impedance Z. A minimum detector is provided to determine if an impedance minimum Zmin has passed through and if such is found, to induce the generator control to reduce the voltage UApp delivered by the device to a value that avoids spark generation as well as desiccation of the tissue.
