Local pixel driver circuitry
An image sensor may include an array of image sensor pixels. Each image sensor pixel in the array may be a global shutter pixel that includes first transistors and second transistors that are substantially larger than the first transistors. The second transistors may receive row control signals from peripheral row drivers formed at the edge of the array. Each pixel may further include local driver circuits interposed between the peripheral row drivers and the second transistors. Each local driver circuit may include a pull-down transistor for driving a row control signal low and a pull-up transistor for driving the row control signal high. Each local driver may optionally be shared among two or more adjacent pixels in a given row. The local drivers help reduce the total capacitive loading at the output of the peripheral row drivers and can therefore help improve row driver performance and minimize integration time.
1. An image sensor, comprising:
an array of image pixels;
a row driver circuit formed at the periphery of the array, wherein the row driver circuit is configured to provide a row control signal to a given row of image pixels in the array via a row control line; and
a plurality of local pixel driver circuits configured to receive signals from the row driver circuit via the row control line, to provide corresponding signals to the given row of image pixels, and to reduce the total amount of capacitive loading on the row control line.
2. The image sensor of claim 1 , wherein each image pixel in the given row of image pixels in the array comprises:
a photosensitive element; and
a transistor coupled to the photosensitive element, wherein the transistor receives the row control signal from one of the plurality of local pixel driver circuits.
3. The image sensor of claim 2 , wherein each of the plurality of local pixel driver circuits comprises a pull-down transistor that is smaller than the transistor in each of the image pixels in the given row.
4. The image sensor of claim 3 , wherein the pull-down transistor in each of the plurality of local pixel driver circuits is at least two times smaller than the transistor in each of the image pixels in the given row.
5. The image sensor of claim 3 , wherein the pull-down transistor in each of the plurality of local pixel driver circuits is at least five to ten times smaller than the transistor in each of the image pixels in the given row.
6. The image sensor of claim 3 , wherein the pull-down transistor in each of the plurality of local pixel driver circuits is directly connected to a local column power supply line that runs perpendicular to the row control line.
7. The image sensor of claim 3 , wherein each of the plurality of local pixel driver circuits further comprises a pull-up transistor that is smaller than the transistor in each of the image pixels in the given row.
8. The image sensor of claim 7 , wherein the pull-down transistor and the pull-up transistor are both n-channel transistors.
9. The image sensor of claim 7 , wherein the pull-down transistor is an n-channel transistor, and wherein the pull-up transistor is a p-channel transistor.
10. The image sensor of claim 7 , wherein the pull-up transistor in each of the plurality of local pixel driver circuits is at least two times smaller than the transistor in each of the image pixels in the given row.
11. The image sensor of claim 7 , wherein the pull-up transistor in each of the plurality of local pixel driver circuits is five to ten times smaller than the transistor in each of the image pixels in the given row.
12. The image sensor of claim 7 , wherein the pull-up transistor in each of the plurality of local pixel driver circuits is directly connected to a local column power supply line that runs orthogonal to the row control line.
13. The image sensor of claim 2 , wherein each image pixel in the given row of image pixels in the array further comprises:
an additional transistor coupled to the photosensitive element, wherein the transistor is an anti-blooming transistor that is at least two times larger than the additional transistor.
14. The image sensor of claim 2 , wherein each image pixel in the given row of image pixels in the array further comprises:
an additional transistor coupled to the photosensitive element, wherein the transistor is a charge transfer transistor that is at least two times larger than the additional transistor.
15. The image sensor of claim 1 , wherein each local pixel driver circuit in the plurality of local pixel driver circuits is shared by at least two image pixels in the given row to reduce area.
16. Circuitry, comprising:
a row driver circuit configured to drive a row line;
an image pixel having a charge transfer transistor, wherein the charge transfer transistor has a gate terminal configured to receive control signals from the row line; and
a local pixel driver circuit coupled between the row line and the gate terminal of the charge transfer transistor.
17. The circuitry of claim 16 , wherein the local pixel driver circuit comprises:
a pull-down transistor directly connected to a first local power supply column line that runs orthogonal to the row line; and
a pull-up transistor directly connected to a second local power supply column line that runs orthogonal to the row line.
18. The circuitry of claim 16 , wherein the local pixel driver circuit includes only one pull-down transistor configured to improve the fall time of the control signals received at the gate terminal of the charge transfer transistor or only one pull-up transistor configured to improve the rise time of the control signals received at the gate terminal of the charge transfer transistor.
19. The circuitry of claim 17 , wherein the charge transfer transistor is at least five times larger than the pull-down transistor in the local pixel driver circuit.
20. An image sensor, comprising:
a row driver configured to drive a row line;
a row of global shutter image pixels configured to receive row control signals from the row line; and
a local pixel driver interposed between the row line and the row of global shutter image pixels, wherein the local pixel driver is shared between at least two image pixels in the row of global shutter image pixels.