A system for measuring electrical charge, comprising a capacitance detector (110) connected to a charge integrator (120) being an operational amplifier with capacitance (Cf) feedback (130), wherein the input stage (121) of the charge integrator (120) comprises a pair of symmetrically connected complementary JFET transistors (T1, T2), the gates of which are connected to the input of the charge integrator (120), characterized in that an n-type transistor (T1) of the complementary pair of transistors (T1, T2) has its drain connected to a voltage regulating system (122).