A system for measuring impedance is disclosed. The system is designed to be connected with an external unknown impedance. The system includes a reference signal generator, an impedance component coupled to the reference signal generator, a local oscillator configured to generate a signal of a selected frequency, a plurality of frequency mixers coupled to the impedance component and the local oscillator and a switch connected across the impedance component in such a way that the impedance component is bypassed when the switch is on.