Disclosed herein is an image sensor for removing a horizontal noise. The
image sensor includes a pixel array including a plurality of unit pixels
located at every row or column; an analog bus located at every row or
column, for transferring output signals of the pixel array; and a readout
circuit for reading the output signals of the pixel array loaded on the
analog bus, wherein the readout circuit includes: a plurality of first
transistors having a drain connected to the column analog bus and a
source connected to a supply voltage; and a second transistor having a
drain connected to a gate of the second transistor and gates of the first
transistors, and a source connected to the supply voltage, wherein, a
size of the second transistor is larger than a size of the first
transistor.