Image sensor including DRAM capacitor and operating method thereof

A pixel comprising:

• photodiodes;
• a first floating diffusion node configured to accumulate charges generated by any one of the photodiodes;
• transmission transistors, each having one end connected to one of the photodiodes and having another end connected to the first floating diffusion node;
• an MCG transistor connected to the first floating diffusion node;
• a second floating diffusion node connected to the MCG transistor;
• an LCG transistor connected to one of the first floating diffusion node and a second floating diffusion node;
• a third floating diffusion node connected to the LCG transistor;
• and
• a dynamic random-access memory (DRAM) capacitor having one end connected to the third floating diffusion node and having another end to which a boosting voltage is applied.

An operating method of an image sensor including a plurality of pixels that each includes a photodiode, a transmission transistor for transmitting charges generated by the photodiode, first to third floating diffusion nodes in which the charges generated by the photodiode are accumulated through the transmission transistor, and a dynamic random-access memory (DRAM) capacitor, the method comprising:

• accumulating overflow charges generated by the photodiode in the first to third floating diffusion nodes and the DRAM capacitor in a state in which the transmission transistor is turned off;
• outputting an overflow image signal corresponding to the overflow charges;
• resetting the first to third floating diffusion nodes and the DRAM capacitor and outputting first to third reset signals respectively corresponding to a plurality of conversion gain modes;
• and
• outputting first to third image signals respectively corresponding to the plurality of conversion gain modes, from the first to third floating diffusion nodes and the DRAM capacitor, after the transmission transistor is turned on.