Low power on-chip impedance detector

An impedance detector for measuring an impedance of a circuit comprises a frequency source, a resistor connected in between the frequency source and the circuit to be measured, a phase shift circuit for applying a phase shift to a signal from the frequency source, a first multiplier for mixing the signal from the frequency source with a signal from the circuit to be measured, a second multiplier for mixing the phase shifted signal with the signal from the circuit to be measured, and a processing circuit for determining an indication of an impedance of the circuit to be measured in dependence on the first mixed signal and the second mixed signal.