Image sensor having high dynamic range
An image sensor according to some example embodiments of the present inventive concepts may operate in a global shutter mode, and each pixel circuit may support a high conversion gain (HCG) mode and a low conversion gain (LCG) mode so as to have high dynamic range (HDR). Accordingly, the image sensor according to some example embodiments of the present inventive concepts may have HDR and may generate a high-quality image.
1 . An image sensor, comprising:
a plurality of pixels positioned in a plurality of rows and a plurality of columns, wherein each pixel of the plurality of pixels includes
a photodiode configured to generate a charge in response to an incident light;
a first floating diffusion node configured to store the charge generated by the photodiode;
a second floating diffusion node selectively connected to the first floating diffusion node and configured to store the charge generated by the photodiode;
a first capacitor selectively connected to an output node and configured to store a charge corresponding to a first reset voltage level of the first floating diffusion node in a state where the first floating diffusion node is electrically disconnected from the second floating diffusion node;
a second capacitor selectively connected to the output node and configured to store a charge corresponding to a first signal voltage level of the first floating diffusion node in the state where the first floating diffusion node is electrically disconnected from the second floating diffusion node;
a third capacitor selectively connected to the output node and configured to store a charge corresponding to a second reset voltage level of the first floating diffusion node in a state where the first floating diffusion node is electrically connected to the second floating diffusion node;
a fourth capacitor selectively connected to the output node and configured to store a charge corresponding to a second signal voltage level of the first floating diffusion node in the state where the first floating diffusion node is electrically connected to the second floating diffusion node; and
a reset transistor connected between the second floating diffusion node and a pixel voltage terminal, the reset transistor configured to reset the first floating diffusion node and the output node while the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are electrically disconnected from the output node.
2 . The image sensor of claim 1 , further comprising:
a source follower configured to amplify and output a voltage level of the first floating diffusion node; and
a precharge select transistor connected between the source follower and the output node,
wherein the image sensor is configured to operate such that, when the output node is reset, the reset transistor and the precharge select transistor are turned on.
3 . The image sensor of claim 2 , further comprising:
a dual conversion gain transistor connected between the second floating diffusion node and the first floating diffusion node,
wherein the image sensor is configured to operate such that, when the output node is reset, the dual conversion gain transistor is turned on.
4 . The image sensor of claim 2 , further comprising:
a precharge transistor and an additional precharge select transistor, which are connected between the source follower and a precharge voltage terminal and are serially connected to the source follower,
wherein the image sensor is configured to operate such that, when the output node is reset, the precharge transistor and the additional precharge select transistor are turned on.
5 . The image sensor of claim 1 , further comprising:
a source follower configured to amplify and output a voltage level of the first floating diffusion node; and
a precharge select transistor connected between the source follower and the output node, and
wherein the image sensor is configured to operate such that, when the output node is precharged, the reset transistor is turned off and the precharge select transistor is turned on.
6 . The image sensor of claim 5 , further comprising:
a precharge transistor and an additional precharge select transistor, which are connected between the source follower and a precharge voltage terminal and are serially connected to the source follower, and
wherein the image sensor is configured to, when the output node is precharged, cause the precharge transistor and the additional precharge select transistor to be turned on.
7 . The image sensor of claim 1 , wherein
a capacity of the first capacitor is greater than a capacity of the third capacitor, and
a capacity of the second capacitor is greater than a capacity of the fourth capacitor.
8 . The image sensor of claim 1 , further comprising:
an ultra conversion gain (ULCG) capacitor selectively connected to the second floating diffusion node and configured to store the charge generated by the photodiode;
a triple conversion gain transistor positioned between the second floating diffusion node and the ULCG capacitor and configured to selectively connect the ULCG capacitor to the second floating diffusion node;
a fifth capacitor selectively connected to the output node and configured to store a charge corresponding to a third reset voltage level of the first floating diffusion node in a state where the ULCG capacitor is electrically connected to the first floating diffusion node and the second floating diffusion node; and
a sixth capacitor selectively connected to the output node and configured to store a charge corresponding to a third signal voltage level of the first floating diffusion node in the state where the ULCG capacitor is electrically connected to the first floating diffusion node and the second floating diffusion node.
9 . The image sensor of claim 8 , wherein
a capacity of the third capacitor is greater than a capacity of the fifth capacitor, and
a capacity of the fourth capacitor is greater than a capacity of the sixth capacitor.
10 . An image sensor, comprising:
a pixel array including a plurality of pixels, wherein each pixel of the plurality of pixels includes
a photodiode configured to generate a charge in response to an incident light;
a high conversion gain (HCG) capacitor corresponding to a first floating diffusion node and configured to integrate the charge generated by the photodiode;
a low conversion gain (LCG) capacitor corresponding to a second floating diffusion node spaced from the first floating diffusion node and configured to integrate the charge generated by the photodiode;
a dual conversion gain transistor configured to electrically connect or disconnect the first floating diffusion node and the second floating diffusion node;
a source follower configured to amplify a voltage level of the first floating diffusion node and to output an amplified voltage level to a first output node;
a first reset capacitor corresponding to a second output node spaced from the first output node and configured to store a charge corresponding to a reset level of the first floating diffusion node in a state where the dual conversion gain transistor is turned off;
a first sampling transistor connected between the first reset capacitor and the second output node and configured to sample a charge that is stored in the first reset capacitor;
a first signal capacitor corresponding to the second output node and configured to store a charge corresponding to a signal level of the first floating diffusion node in the state where the dual conversion gain transistor is turned off;
a second sampling transistor connected between the first signal capacitor and the second output node and configured to sample a charge that is stored in the first signal capacitor;
a second reset capacitor corresponding to the second output node and configured to store a charge corresponding to a reset level of the first floating diffusion node in a state where the dual conversion gain transistor is turned on;
a third sampling transistor connected between the second reset capacitor and the second output node and configured to sample a charge that is stored in the second reset capacitor;
a second signal capacitor corresponding to the second output node and configured to store a charge corresponding to a signal level of the first floating diffusion node in the state where the dual conversion gain transistor is turned on;
a fourth sampling transistor connected between the second signal capacitor and the second output node and configured to sample a charge that is stored in the second signal capacitor;
a precharge select transistor configured to electrically connect and disconnect the first output node and the second output node; and
a reset transistor connected between the second floating diffusion node and a pixel voltage terminal, the reset transistor configured to reset the first floating diffusion node and the second output node while the first reset capacitor, the second reset capacitor, the first signal capacitor, and the second signal capacitor are electrically disconnected from the first output node.
11 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that, during a reset time in a global signal dump period, the reset transistor and the dual conversion gain transistor are turned on.
12 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that, during a second reset settling time in a global signal dump period, the third sampling transistor is turned on in a state where the reset transistor is turned off and the dual conversion gain transistor is turned on.
13 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that, during a first reset settling time in a global signal dump period, the first sampling transistor is turned on in a state where each of the reset transistor and the dual conversion gain transistor is turned off.
14 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that, during a first signal settling time in a global signal dump period, the second sampling transistor is turned on in a state where each of the reset transistor and the dual conversion gain transistor is turned off.
15 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that, during a second signal settling time in a global signal dump period, the fourth sampling transistor is turned on in a state where the reset transistor is turned off and the dual conversion gain transistor is turned on.
16 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that, during a first precharging time in a read-out period, the precharge select transistor is turned on in a state where each of the reset transistor and the dual conversion gain transistor is turned on.
17 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that,
during a first reset read-out time in a read-out period, the first sampling transistor is turned on in a state where at least one of the reset transistor or the dual conversion gain transistor is turned off, and the precharge select transistor is turned off, and
during a second reset read-out time in the read-out period, the third sampling transistor is turned on in a state where the precharge select transistor is turned off.
18 . The image sensor of claim 10 , further comprising:
a precharge transistor connected to the first output node,
wherein the image sensor is configured to operate such that, during a second precharging time in a read-out period, each of the precharge select transistor and the precharge transistor is turned on in a state where at least one of the reset transistor or the dual conversion gain transistor is turned off.
19 . The image sensor of claim 10 , wherein the image sensor is configured to operate such that,
during a first signal read-out time in a read-out period, the second sampling transistor is turned on in a state where the precharge select transistor is turned off, and
during a second signal read-out time in the read-out period, the fourth sampling transistor is turned on in a state where the precharge select transistor is turned off.