A method for conversion of a time interval to a digital word using a successive approximation scheme consisting in a detection of a beginning and of an end of the time interval by the use of a control module, and in assignment of a corresponding binary value represented by n-bit output digital word to the time interval by the use of the control module, characterized in that the time interval is mapped to a difference of a length of a reference time and a length of a signal time, while the reference time is generated from an instant (t 1) when the beginning of the time interval is detected by the use of the control module, and the signal time is generated from an instant (t 2) when the end of the time interval is detected by the use the control module, whereas generation of the reference time and the signal time is terminated at the same instant (t 3) and a generation of the reference time is realized by charging a capacitor using a reference current source (I R), while this capacitor is selected by the use of the control module from a set of capacitors comprising capacitors (C n-1, C n-2,..., C 1, C 0), such that a capacitance of a capacitor of a given index is twice as high as a capacitance of a capacitor of the previous index, and a capacitor (C n-1) of the highest capacitance in the set of capacitors is selected first, while the selected capacitor is charged as long as a reference voltage (U R) increasing on the selected capacitor and compared to a threshold voltage (U TH) by the use of a reference comparator (K R) reaches the threshold voltage (U TH), and then, a next capacitor in the set of capacitors is started to be charged while this capacitor has the highest capacitance among the capacitors that have not been charged yet, and the reference voltage (U R) increasing on this capacitor being charged is compared to the threshold voltage (U TH) by the use of the reference comparator (K R), and the cycle is repeated to the end of generation of both time intervals, while generation of the signal time is realized by charging a capacitor by the use of a signal current source (I S), while this capacitor is selected by the use of the control module from the set of capacitors having the highest capacitance among the capacitors that have not been charged yet, and the selected capacitor is charged as long as a signal voltage (U S) increasing on this capacitor and compared to the threshold voltage (U TH) by the use of a signal comparator (K S) reaches the threshold voltage (U TH), and then, a next capacitor in the set of capacitors is started to be charged by the use of a signal current source (I S) while this capacitor is selected in a similar way as for the selection of a next capacitor for the above-mentioned generation of the reference time and the cycle is repeated, and the generation of the reference time and the generation of the signal time are terminated during the time when the capacitor (C 0) of the lowest capacitance in the set of capacitors is charged, and when the reference voltage (U R) increasing on a capacitor charged by the use of the reference current source (I R), or when the signal voltage (U S) increasing on a capacitor charged by the use of the signal current source (I S) reaches the threshold voltage (U TH).