1. A circuit for measuring absolute spread in capacitors implemented in planary technology characterised in that it comprises a charge pump supplying a charge current to an internal capacitor (Cint), the voltage across the internal capacitor (Cint) being coupled through a comparator for comparing said voltage with first and second threshold levels, to a bistable multivibrator for reversing the direction of the charge current to charge the internal capacitor (Cint) when said voltage decreases below the second threshold level and to decharge the internal capacitor (Cint), when said voltage increases above the first threshold level, a reference voltage determining the charge current, as well as the voltage range between said first and second threshold levels, an output signal, of the bistable multivibrator being coupled to frequency measuring means to compare the repetition frequency thereof with a reference frequency.