Magnetic field measuring apparatus and flux quantum calculating method

A flux quantum calculating method for calculating a flux quantum using a magnetic field measuring apparatus that includes a digital flux locked loop circuit, the flux quantum calculating method comprising:

• converting, by a first analog-to-digital converter included in the digital flux locked loop circuit, a periodically changing voltage, output from a superconducting quantum interference device according to a change in a magnetic field, into a digital value;
• integrating, by a digital integrator included in the digital flux locked loop circuit, the digital value output from the first analog-to-digital converter, into an integrated value;
• converting, by a first voltage-to-current converter included in the digital flux locked loop circuit, the integrated value output from the digital integrator, into a current;
• generating, by a first coil included in the digital flux locked loop circuit, the magnetic field received by the superconducting quantum interference device, based on the current output from the first voltage-to-current converter;
• and
• calculating, by a calculating device included in the magnetic field measuring apparatus, a digital value indicating a flux quantum based on the digital value output from the first analog-to-digital converter when the first analog-to-digital converter converts the periodically changing voltage output from the superconducting quantum interference device upon receiving the magnetic field generated by a current that is obtained by converting a voltage generated by a voltage generator.