Circuit for measuring variations in the capacitance of a variable capacitor using a continuously rebalanced detection bridge

A circuit for measuring variations in the capacitance of a variable capacitor, wherein the circuit comprises:

• an oscillator generating an alternating signal;
• a detection bridge comprising first and second branches connected to the oscillator, the first branch including the variable capacitor connected in series with a variable capacitance diode, while the second branch comprises a capacitor connected in series with a variable capacitance diode;
• a differential stage having its inputs connected to respective ones of the branches at their common points between their capacitors and their variable capacitance diodes;
• a DC bias circuit for biasing the common point of the second branch;
• synchronous demodulation means following the differential stage and connected to the oscillator for delivering a DC unbalance signal;
• and
• a feedback line injecting the unbalance signal to the common point of the first branch to continuously rebalance the detection bridge.