An electric circuit arrangement and a measuring method for a galvanically insulated, AC/DC sensitive differential current measurement having a high resolution having: a toroid current transformer having at least one secondary winding for detecting a differential current; a driver circuit for powering the secondary winding; a first oscillator circuit for controlling the driver circuit and for generating a time-modulated binary oscillator signal having dwell times in a state 1 and a state 2; a second oscillator circuit for determining the corresponding dwell time in the states 1 and 2 in high resolution by means of a clock signal having a clock rate independent of the oscillator signal; an evaluation device for evaluating the dwell time; and a data interface for outputting a differential-current measuring value; the driver circuit and the second oscillator circuit each being realized as structurally individual, integrated circuits.