A digital circuit device includes a power supply circuitry, a digital circuitry, a digital circuitry, and a protection circuitry. The power supply circuitry is configured to output a supply voltage. The digital circuitry is configured to be driven by the supply voltage, and is configured to perform at least one operation according to a first clock signal. The protection circuitry is configured to generate the first clock signal according to at least one of a voltage drop of the supply voltage and a load signal sent from the digital circuitry.