Method and apparatus for automatic gain control

An apparatus for automatic gain control, the apparatus comprising:

• a sinewave generator module;
• and
• a gain control signal generator module;
• wherein the sinewave generator module is configured to receive a first signal and a second signal, wherein the first signal is proportional to a sinusoid of a measured parameter and the second signal corresponds to the first signal shifted by a quarter of a period of the sinusoid;
• the sinewave generator module is further configured to generate an approximated sinusoidal function over time by determining values of a shifted sine function with a first frequency at a plurality of sampling points, wherein a phase shift and an amplitude of the shifted sine function are based on the first signal and second signal;
• the gain control signal generator module is configured to generate a third signal that is proportional to an amplitude spectrum of the approximated sinusoidal function at the first frequency;
• and
• the gain control signal generator module is further configured to output the third signal to a circuit for measuring the measured parameter, wherein the apparatus for automatic gain control is connected to the circuit and the third signal is used for gain control of the circuit.