Image sensor
An image sensor including: a pixel array including pixels; and a logic circuit including a row decoder to drive selected pixels, a column decoder to vary exposure time periods for a portion of the selected pixels, and a readout circuit to obtain pixel signals from the selected pixels, wherein each of the pixels includes a photodiode, a first transfer transistor connected between the photodiode and a first floating diffusion region, a second transfer transistor connected between the first floating diffusion region and a second floating diffusion region, a first reset transistor and a switch transistor connected to each other in series between a power node and the first floating diffusion region, a second reset transistor connected between the power node and the second floating diffusion region, a source-follower transistor connected to the second floating diffusion region, and a select transistor connected to the source-follower transistor.
1 . An image sensor, comprising:
a pixel array including a plurality of pixels arranged in a first direction and a second direction intersecting the first direction; and
a logic circuit including a row decoder configured to drive selected pixels disposed in the same position in the second direction among the plurality of pixels, a column decoder configured to vary exposure time periods for a portion of the selected pixels, and a readout circuit configured to obtain pixel signals from the selected pixels,
wherein each of the plurality of pixels includes at least one photodiode, a first transfer transistor connected between the photodiode and a first floating diffusion region, a second transfer transistor connected between the first floating diffusion region and a second floating diffusion region, a first reset transistor and a switch transistor connected to each other in series between a power node configured to supply a power voltage and the first floating diffusion region, a second reset transistor connected between the power node and the second floating diffusion region, a source-follower transistor connected to the second floating diffusion region, and a select transistor connected to the source-follower transistor.
2 . The image sensor of claim 1 , wherein a capacity of the first floating diffusion region is greater than a capacity of the second floating diffusion region.
3 . The image sensor of claim 1 ,
wherein each of the plurality of pixels includes a plurality of sub-pixels,
wherein each of the plurality of sub-pixels includes the photodiode and the first transfer transistor, and
wherein, in each of the plurality of pixels, the plurality of sub-pixels share the second transfer transistor, the first reset transistor, the switch transistor, the second reset transistor, the source-follower transistor and the select transistor.
4 . The image sensor of claim 3 ,
wherein the selected pixels include at least one first pixel having a first exposure time period, and at least one second pixel having a second exposure time period shorter than the first exposure time period, and
wherein, while the row decoder drives the selected pixels, the column decoder turns on the switch transistor of the first pixel during a first time period and turns on the switch transistor of the second pixel during a second time period later than the first time period.
5 . The image sensor of claim 4 , wherein the column decoder turns on the switch transistor of each of the first pixel and the second pixel during the first time period, and turns off the switch transistor of the first pixel and turns on the switch transistor of the second pixel during the second time period.
6 . The image sensor of claim 4 , wherein the column decoder turns on the switch transistor of the first pixel and turns off the switch transistor of the second pixel during the first time period, and turns off the switch transistor of the first pixel and turns on the switch transistor of the second pixel during the second time period.
7 . The image sensor of claim 4 ,
wherein the selected pixels further include at least one third pixel having a third exposure time period shorter than the second exposure time period, and
wherein, while the row decoder drives the selected pixels, the column decoder turns on the switch transistor of the third pixel during a third time period later than the second time period.
8 . The image sensor of claim 7 ,
wherein the column decoder turns on the switch transistor of each of the first pixel, the second pixel and the third pixel during the first time period,
wherein the column decoder turns off the switch transistor of the first pixel and turns on the switch transistor of each of the second pixel and the third pixel during the second time period, and
wherein the column decoder turns off the switch transistor of each of the first pixel and the second pixel and turns on the switch transistor of the third pixel during the third time period.
9 . The image sensor of claim 7 ,
wherein the column decoder turns on the switch transistor of the first pixel and turns off the switch transistor of each of the second pixel and the third pixel during the first time period,
wherein the column decoder turns on the switch transistor of the second pixel and turns off the switch transistor of each of the first pixel and the third pixel during the second time period, and
wherein the column decoder turns on the switch transistor of the third pixel and turns off the switch transistor of each of the first pixel and the second pixel during the third time period.
10 . The image sensor of claim 1 , wherein the readout circuit obtains a reset voltage from each of the selected pixels during a time period in which the second reset transistor is turned on, and obtains a pixel voltage during a time period in which the second transfer transistor is turned on.
11 . The image sensor of claim 10 , wherein the second transfer transistor is turned on together with the first transfer transistor.
12 . The image sensor of claim 1 , wherein an exposure time period of each of the selected pixels is a time from a last time point at which the switch transistor transitions from a turned-on state to a turned-off state to a time point at which the second transfer transistor transitions from the turned-off state to the turned-on state.
13 . An image sensor, comprising:
a pixel array that includes a plurality of pixels; and
a logic circuit configured to control the pixel array,
wherein each of the plurality of pixels includes at least one photodiode, a first transfer transistor directly connected to the photodiode, a second transfer transistor connected to the first transfer transistor, a switch transistor connected to a node between the first transfer transistor and the second transfer transistor, a first reset transistor connected between a power node configured to supply a power voltage and the switch transistor, a source-follower transistor having a gate connected to the second transfer transistor, a second reset transistor connected between the gate of the source-follower transistor and the power node, and a select transistor connected between the source-follower transistor and an output line, and
wherein, in a read operation for each of the plurality of pixels, the logic circuit turns on the first reset transistor and the first transfer transistor in two or more reset time periods, and obtains a pixel signal in a readout time period in which the first transfer transistor and the second transfer transistor are turned on.
14 . The image sensor of claim 13 , wherein the logic circuit turns on the second reset transistor between the latest reset time period among the reset time periods and the readout time period.