System and method for auto calibration in a power blackout sensing system

A power blackout sensing system comprising:

• a voltage regulator configured to receive one of three phase wires and a neutral wire of a primary power source that provides an alternating current (AC) power;
• a calibration amplifier comprising a plurality of transistors and a variable resistor that is configured to change in response to clock pulses;
• a voltage sense amplifier;
• a sensing block configured to receive the neutral wire of the primary power source and comprising a coupled inductor device and the voltage sense amplifier;
• and
• a secondary power source,
• wherein the voltage regulator is coupled to a switch and generates a direct current (DC) voltage signal, and
• wherein the coupled inductor device of the sensing block comprises a pull-down resistor, wherein the coupled inductor device is configured to convert a voltage signal of the neutral wire to a 180-degree phase-shifted voltage signal of the neutral wire and generate a reference voltage signal using the pull-down resistor,
• wherein the voltage sense amplifier is configured to amplify a voltage gap between the 180-degree phase-shifted voltage signal of the neutral wire and the reference voltage signal,
• wherein, during a calibration cycle, one of the plurality of transistors of the calibration amplifier switches on in each calibration step based on a plurality of enable signals, and a gain of the calibration amplifier changes until an output voltage of the calibration amplifier exceeds the reference voltage and is set to a calibrated gain,
• wherein the calibration amplifier outputs the output voltage by amplifying an input voltage using the calibrated gain, and
• wherein the sensing block detects a phantom voltage on the one of three phase wires and provides an output signal corresponding the secondary power source during a blackout period.