A control circuit for use with a four terminal sensor, the sensor having first and second drive terminals and first and second measurement terminals, the control circuit arranged to drive at least one of the first and second drive terminals with an excitation signal, to sense a voltage difference between the first and second measurement terminals, and control the excitation signal such that the voltage difference between the first and second measurement terminals is within a target range of voltages, and wherein the control circuit includes N poles in its transfer characteristic and N−1 zeros in its transfer characteristic such that when a loop gain falls to unity the phase shift around a closed loop is not substantially 2π radians or a multiple thereof, where N is greater than 1.