A scan frequency detector is responsive to a horizontal synchronization signal to generate a data signal that is indicative of the horizontal scan frequency. A digital-to-analog (D/A) converter produces from the data signal an analog, output signal at a first level, when the horizontal frequency is within a first range of values, at a second level, when the horizontal frequency is within a second range of values and at a third level, when the horizontal frequency is within a third range of values. A first switch of a switched S-capacitor arrangement, is turned on, when the output signal is at the first level. The first switch and a second switch of the switched S-capacitor arrangement, are turned on, when the output signal is at the second level. Both the first and second switches are turned off, when the output signal is at the third level. The third and second levels are distinguished by a level detector that includes a zener diode.