a booster configured to amplify a current amount between a power voltage terminal to which a power voltage is applied and a ground terminal to generate a sensing voltage; and

an oscillator configured to output a sensing signal of which a frequency is adjusted in response to the sensing voltage,

wherein the booster includes a first transistor having a first size and a second transistor having a second size greater than the first size, the first and second transistors being of a same conductivity type,

wherein the first transistor and the second transistor are coupled in series between the power voltage terminal and the ground terminal, and

wherein the oscillator includes a plurality of transistors having a third size greater than the first size.