The invention relates to a method and system and microchip for determining impedance of a variable impedance component. The method comprises tuning a tunable oscillator over a predefined tuning range, the tunable oscillator having the variable impedance component coupled as a load thereof. The frequency response of the tunable oscillator is measured as a function of said tuning. Finally, the measured frequency response is analyzed for determining the impedance of the variable impedance component. The invention makes possible to manufacture smaller and simpler monolithic sensor microchips.