Image sensor and operation method thereof

An operation method of an image sensor, wherein the image sensor comprises a first pixel circuit, a first column readout circuit, and a second column readout circuit, the first pixel circuit comprises a first pixel unit, a first transfer transistor, a first reset transistor, a first readout transistor, and a first capacitor, the first column readout circuit comprises a first circuit node, wherein a first terminal of the first reset transistor and a first terminal of the first readout transistor are coupled to the first circuit node, and a second terminal of the first readout transistor is coupled to the bias transistor, wherein the operation method comprises:

• receiving a first reset signal through a control terminal of the first reset transistor during a reset period, and receiving a transfer signal first through a control terminal of the transfer transistor to reset a voltage of a first floating diffusion node, and then receiving a pull-down control signal through a control terminal of a second transistor to pull down the voltage of the first floating diffusion node;
• receiving a transfer signal through the control terminal of the transfer transistor during a readout period, so that the first readout transistor is turned on according to the ramp signal and a charge accumulated by the first floating diffusion node and provided by the first pixel unit, and reading out the charge accumulated by the first floating diffusion node to generate a readout signal from the first circuit node;
• and
• receiving the first reset signal through the control terminal of the first reset transistor during a pull-down period, and receiving a pull-down control signal through a control terminal of the second transistor to pull down the voltage of the first floating diffusion node.