CMOS image sensor

1. A pixel layout of a CMOS image sensor for arranging a pixel comprising:

two photodiodes;

a floating diffusion region shared by the two photodiodes;

two transfer transistors, each diagonally disposed between two photodiodes and the floating diffusion region, wherein each of the photodiodes and transfer transistors are symmetrical with respect to the floating diffusion region; and

a reset transistor, a drive transistor and a select transistor disposed in straight alignment with the floating diffusion region.

2. The pixel layout as recited in claim 1 , wherein unit pixels are laid out such that one unit pixel is formed upside down in comparison with a neighboring unit pixel so that the unit pixels are engaged with each other.

3. The pixel layout as recited in claim 1 , wherein said image sensor comprises:

a plurality of photodiodes for sensing light to thereby generate photoelectric charges;

a plurality of transfer transistors for transferring photoelectric charges of corresponding photodiodes in response to a first control signal;

a floating diffusion region for receiving photoelectric charges transferred by the plurality of transfer transistors;

a reset transistor connected between a power supply voltage and the floating diffusion region for resetting the floating diffusion region by controlling a voltage loaded on the floating diffusion region in response to a second control signal;

a drive transistor connected between the power supply voltage and the floating diffusion region to serve as a source follower buffer amplifier; and

a select transistor connected between the drive transistor and a pixel output terminal for performing an addressing operation in response to a third control signal.

4. The pixel layout as recited in claim 1 , further comprising:

an active region for forming source/drain regions, the two photodiodes, and the floating diffusion region between gate patterns of each transistor in a substrate, wherein the active region includes a first active region having a “U” shape and a second active region having an “I” shape.

5. The pixel layout as recited in claim 4 , wherein the floating diffusion region is are formed between two photodiodes in the first active region, and two gate patterns of the transfer transistors are disposed between the two photodiodes and the floating diffusion in the first active region.

6. The pixel layout as recited in claim 4 , wherein

the gate patterns of the reset transistor, the drive transistor, the select transistor are formed on the second active region, and

the source/drain regions therebetween are formed in the second active region.