Analog-to-digital converter, image sensor including the same, and apparatus including image sensor

An image sensor comprising:

• a pixel unit including at least one pixel outputting an analog signal according to light input from an outside;
• and
• an analog digital conversion unit including at least one analog-to-digital converter converting the analog signal into a digital signal,
• the at least one analog-to-digital converter including,
• a signal processing unit generating an operational amplifier output voltage in response to the analog signal and a DAC output voltage in a sigma-delta operating period and generating the operational amplifier output voltage in response to a feedbacked operational amplifier output voltage and the DAC output voltage in a cyclic operating period;
• a control unit generating a DAC control signal by comparing the operational amplifier output voltage with a first reference voltage in the sigma-delta operating period and obtaining high order M-bits of data and generating the DAC control signal by comparing the operational amplifier output voltage with second and third reference voltages in the cyclic operating period and obtaining low order N-bits of data;
• and
• a digital analog converter generating the DAC output voltage in response to the DAC control signal.

An analog-to-digital converter comprising:

• an internal circuit receiving an input signal and generating an output signal;
• a sigma-delta controller controlling to operate the internal circuit as a sigma-delta analog-to-digital converter when the input signal is input from an outside and obtaining high order M-bits of a digital signal among digital signals corresponding to the input signal by inputting the output signal thereto;
• and
• a cyclic controller controlling to operate the internal circuit as a cyclic analog-to-digital converter after obtaining the high order M-bits of the digital signal and obtaining low order N-bits of a digital signal among the digital signals by inputting the output signal thereto,
• wherein the internal circuit includes:
• a signal processing unit generating the output signal in response to the input signal and a reference voltage when the internal circuit operates to serve as the sigma-delta analog-to-digital converter and generating the output signal in response to the output signal of the internal circuit, which has been feedbacked, and the reference voltage;
• and
• a reference voltage generating unit controlled by the sigma-delta controller and the cyclic controller and generating the reference voltage having a different value according to a magnitude of the output signal.