A driving circuit of an image sensor is provided. The driving circuit can include a pixel array where pixel circuits receiving light and converting the received light into an electrical signal are arranged in columns, an analog-to-digital (ADC) block including a plurality of ADC circuits receiving an analog image signal from pixel circuits arranged in the same column and converting the received analog image signal into a digital signal, and an ADC controller outputting a global signal to control each operation of the ADC circuit. The ADC controller can allow the ADC circuits in the ADC block to operate separately according to at least two timings.