Image sensor device with first and second source followers and related methods
An image sensor device may include an array of image sensing pixels arranged in rows and columns. Each image sensing pixel may include an image sensing photodiode, a first source follower transistor coupled to the image sensing photodiode, and a switch coupled to the image sensing photodiode. Each image sensor device may include a second source follower transistor coupled to the switch, and a row selection transistor coupled to the first and second source follower transistors.
1. An image sensing pixel, comprising:
an image sensing photodiode comprising an anode and a cathode, wherein the anode of the image sensing photodiode is coupled to a first reference voltage;
a first source follower transistor comprising a control terminal coupled to the cathode of the image sensing photodiode;
a switch comprising a first terminal coupled to the control terminal of the first source follower transistor, a second terminal coupled to the first reference voltage, and a node between the first terminal and the second terminal; and
a second source follower transistor comprising a control terminal coupled to the node of the switch, wherein the switch comprises a third transistor and a fourth transistor coupled in series with the third transistor, wherein:
the third transistor comprises a first conduction terminal forming the first terminal of the switch;
a second conduction terminal of the third transistor and a first conduction terminal of the fourth transistor are coupled to form the node of the switch; and
a second conduction terminal of the fourth transistor forms the second terminal of the switch.
2. The image sensing pixel of claim 1 , wherein the third transistor and the fourth transistor have different conductivity types.
3. The image sensing pixel of claim 2 , wherein the third transistor and the fourth transistor comprise a p-type transistor and an n-type transistor, respectively.
4. The image sensing pixel of claim 1 , wherein a control terminal of the third transistor and a control terminal of the fourth transistor are coupled to receive a same switch command signal.
5. The image sensing pixel of claim 1 , wherein a first conduction terminal of the first source follower transistor and a first conduction terminal of the second source follower transistor are coupled to a second reference voltage.
6. The image sensing pixel of claim 1 , wherein a second conduction terminal of the first source follower transistor is coupled to a second conduction terminal of the second source follower transistor.
7. The image sensing pixel of claim 6 , further comprising a row selection transistor comprising a first conduction terminal coupled to the second conduction terminal of the second source follower transistor.
8. The image sensing pixel of claim 7 , wherein the row selection transistor further comprises a second conduction terminal coupled to a column line.
9. The image sensing pixel of claim 1 , further comprising a transfer transistor comprising a first conduction terminal coupled to the cathode of the image sensing photodiode, a second conduction terminal coupled to the control terminal of the first source follower transistor, and a control terminal coupled to receive a read command signal.
10. The image sensing pixel of claim 1 , further comprising a reset transistor comprising a first conduction terminal coupled to a second reference voltage, a second conduction terminal coupled to the control terminal of the first source follower transistor, and a control terminal coupled to receive a reset command signal.
11. The image sensing pixel of claim 1 , further comprising a sensing node photodiode comprising a cathode and an anode, wherein the cathode of the sensing node photodiode is coupled to the control terminal of the first source follower transistor, and wherein the anode of the sensing node photodiode is coupled to the first reference voltage.
12. An electronic device, comprising:
a processor; and
an array of image sensing pixels coupled to the processor and arranged in rows and columns, each image sensing pixel comprising:
an image sensing photodiode comprising an anode and a cathode, wherein the anode of the image sensing photodiode is coupled to a first reference voltage;
a first source follower transistor comprising a control terminal coupled to the cathode of the image sensing photodiode;
a switch comprising a first terminal coupled to the control terminal of the first source follower transistor, a second terminal coupled to the first reference voltage, and a node between the first terminal and the second terminal; and
a second source follower transistor comprising a control terminal coupled to the node of the switch, wherein the switch comprises a third transistor and a fourth transistor coupled in series with the third transistor, wherein:
the third transistor is configured to be conducting when the fourth transistor is non-conducting; and
the fourth transistor is configured to be non-conducting when the fourth transistor is conducting.
13. The electronic device of claim 12 , wherein:
the third transistor comprises a first conduction terminal forming the first terminal of the switch;
a second conduction terminal of the third transistor and a first conduction terminal of the fourth transistor are coupled to form the node of the switch; and
a second conduction terminal of the fourth transistor forms the second terminal of the switch.
14. The electronic device of claim 12 , wherein a control terminal of the third transistor and a control terminal of the fourth transistor are coupled to receive a same switch command signal.
15. The electronic device of claim 12 , wherein a first conduction terminal of the first source follower transistor and a first conduction terminal of the second source follower transistor are coupled to a second reference voltage.
16. The electronic device of claim 12 , wherein a second conduction terminal of the first source follower transistor is coupled to a second conduction terminal of the second source follower transistor.
17. The electronic device of claim 16 , wherein each image sensing pixel further comprises a row selection transistor comprising a first conduction terminal coupled to the second conduction terminal of the second source follower transistor.
18. The electronic device of claim 17 , wherein the row selection transistor further comprises a second conduction terminal coupled to a column line.
19. The electronic device of claim 12 , wherein each image sensing pixel further comprises a sensing node photodiode comprising a cathode and an anode, wherein the cathode of the sensing node photodiode is coupled to the control terminal of the first source follower transistor, and wherein the anode of the sensing node photodiode is coupled to the first reference voltage.
20. The electronic device of claim 12 , wherein each image sensing pixel further comprises a reset transistor comprising a first conduction terminal coupled to a second reference voltage, a second conduction terminal coupled to the control terminal of the first source follower transistor, and a control terminal coupled to receive a reset command signal.