US Patent 9274151 Fast wideband frequency comparator

A frequency comparator outputs an input reference signal and a comparison target signal as pulse-form signals, and is charged or discharged with a voltage corresponding to the reference signal to output a reference voltage having a variable first frequency range, and charged or discharged with a voltage corresponding to the comparison target signal to output a comparison target voltage having a variable second frequency range. The frequency comparator compares the reference voltage having the first frequency range and the comparison output voltage having the second frequency range.