Method and system for measuring capacitance difference between capacitive elements

A system for measuring a capacitance difference (ΔC) between a first capacitive element (DUT1) and a second capacitive element (DUT2), the system comprising the following components:

• means for supplying voltage provided for supplying a first DC voltage (Vhigh), a second DC voltage (Vlow) which is different from the first DC voltage, and a third DC voltage (GND);
• a measurement circuit comprising:
• a first switch (T1) and a second switch (T2) matched to the first switch (T1);
• a first node (N1) and a second node (N2) between which the first capacitive element (DUT1) is connectable, the second node (N2) being connectable to the third DC voltage (GND) via the first switch (T1);
• a third node (N3) and a fourth node (N4) between which the second capacitive element (DUT2) is connectable, the fourth node (N4) being connectable to the third DC voltage (GND) via the second switch (T2), and the second and fourth nodes (N2, N4) being connected to each other;
• the voltage supply means being provided for applying in a first phase the first DC voltage (Vhigh) to the first node (N1) and the second DC voltage (Vlow) to the third node (N3), to charge the capacitive elements (DUT1, DUT2), and applying in a second phase the first and second DC voltages (Vhigh, Vlow) alternatingly to the first and third nodes (N1, N3), for alternatingly charging and discharging the capacitive elements (DUT1, DUT2);
• a controller provided for generating non-overlapping clock signals (Vset1, Vset2) for alternately closing the first and second switches (T1, T2) in the first and second phases, and for controlling the alternations of the first and second DC voltages (Vhigh, Vlow) in the second phase at such instances that these alternations occur while either the first switch or the second switch is closed, such that in the first phase first resulting currents flow through at least one of the first and second switches, which are proportional to the capacitance of the measurement circuit, and that in the second phase second resulting currents flow through at least one of the first and second switches, which are proportional to the capacitance of the measurement circuit together with the capacitance difference (ΔC);
• means for measuring the first resulting currents (I1, I2) flowing through at least one of the first and second switches in the first phase and the second resulting currents (I1, I2) flowing through at least one of the first and second switches during the second phase;
• and
• means for determining the capacitance difference (ΔC) from a subtraction of the first and second resulting currents measured during respectively the first phase and the second phase.