A signal sensing circuit is provided. The signal sensing circuit comprises a first current-to-voltage circuit, a second current-to-voltage circuit and an impedance shifting circuit. The first current-to-voltage circuit converts a first input current into a first voltage that is directly proportional to a first impedance. The second current-to-voltage circuit converts a second input current into a second voltage that is directly proportional to a second impedance. The impedance shifting circuit generates a third voltage according to the first voltage, wherein the first impedance/the second impedance=K(first voltage/third voltage), where K is a real number.