Generating an output pulse signal (Y), which has an output signal period (T y ), which is divided by a magnitude transition into a leading part (LP) and a trailing part (TP). During each output signal period (T y ) altering means (27 to 36) determine in a coarse and fine way a duration (T LP , T TP ) of one or both of said output signal period parts (LP, TP) by using a clock signal (Cx) of different clock cycle durations (T Cx0 , T Cx1 , T Cx2 ), dependent on a value of a first digital number (Dl) and a value of a second, less significant digital number (D3, D5), respectively.