Pixel, pixel driving circuit, and vision sensor including the same
A pixel includes a photoelectric device, a current readout unit configured to detect an electric current flowing in the photoelectric device to generate an input voltage, an event determination unit configured to determine an event occurrence and an event type responsive to the input voltage, and configured to output an event detection signal, and an event output unit configured to store the event detection signal for an event-storage period and configured to output the stored event detection signal responsive to an expiration of the event-storage period.
1. A pixel comprising:
a photoelectric device;
a current readout unit configured to detect an electric current flowing in the photoelectric device to generate an input voltage;
an event determination unit configured to determine an event occurrence and an event type responsive to the input voltage, and configured to output an event detection signal; and
an event output unit configured to store the event detection signal for an event-storage period, and configured to output the event detection signal stored in the event output unit.
2. The pixel of claim 1 , wherein the event output unit comprises:
a storage unit connected to an event output terminal and configured to store the event detection signal; and
a switch unit connected between the storage unit and an input terminal for the event detection signal.
3. The pixel of claim 2 , wherein the event output unit is configured to store the event detection signal in the storage unit responsive to the switch unit being in a closed state, and is configured to output the event detection signal that is stored in the storage unit through the event output terminal responsive to the switch unit being in an open state.
4. The pixel of claim 2 , wherein the storage unit comprises:
an on-capacitor connected between a first node connected to an on-event output terminal and a ground; and
an off-capacitor connected between a second node connected to an off-event output terminal and a ground.
5. The pixel of claim 4 , wherein the switch unit comprises:
an on-switch connected between the on-capacitor and an input terminal for an on-event detection signal; and
an off-switch connected between the off-capacitor and an input terminal for an off-event detection signal.
6. The pixel of claim 2 , wherein the storage unit comprises:
a first on-capacitor connected between a first node connected to an on-event output terminal and a ground;
a second on-capacitor connected between a third node connected to an on-switch and a ground;
a first switching device connected between the first node and the third node;
a first off-capacitor connected between a second node connected to an off-event output terminal and a ground;
a second off-capacitor connected between a fourth node connected to an off-switch and a ground; and
a second switching device connected between the second node and the fourth node.
7. The pixel of claim 2 , wherein the storage unit comprises:
a first on-capacitor connected between a first node connected to an on-event output terminal and a ground;
a second on-capacitor connected between a third node connected to a second on-switch and a ground;
a first on-switch connected between the first node and the third node;
a first off-capacitor connected between a second node connected to an off-event output terminal and a ground;
a second off-capacitor connected between a fourth node connected to a second off-switch and a ground; and
a first off-switch connected between the second node and the fourth node.
8. The pixel of claim 1 , wherein the event determination unit is configured to activate an on-event detection signal responsive to the electric current flowing in the photoelectric device increases to and/or exceeds a predetermined value.
9. The pixel of claim 1 , wherein the event determination unit is configured to activate an off-event detection signal responsive to the electric current flowing in the photoelectric device decreases to and/or falls below a predetermined value.
10. The pixel of claim 1 , further comprising an event reset unit configured to reset the pixel to an initial state in response to an input reset signal.
11. A pixel driving circuit comprising:
a column driver configured to generate a signal to select any one among a plurality of column lines of a pixel array;
a row driver configured to detect whether an event has occurred from respective pixels of the pixel array connected to the one of the plurality of column lines selected by the column driver;
a controller configured to control operation timings of the column driver and the row driver; and
an address generator configured to generate and output an address of one of the pixels in which the event has occurred and was detected by the row driver,
wherein the pixel driving circuit is implemented as a digital block, and
wherein the controller is configured to generate at least one of a global hold signal opening a plurality of switches in concert included in each of a plurality of pixels of the pixel array to store an event detection signal by each of the plurality of pixels, and a global reset signal resetting data of the plurality of pixels of the pixel array.
12. The pixel driving circuit of claim 11 , wherein the row driver is configured to generate a reset signal resetting data of the pixels of the pixel array connected to the one of the plurality of column lines currently selected by the column driver.
13. The pixel driving circuit of claim 12 , wherein the row driver is further configured to provide the reset signal to pixels of the pixel array connected to the one of the plurality of column lines currently selected by the column driver in which an event has occurred.
14. The pixel driving circuit of claim 11 , wherein the row driver is configured to generate a signal pulling up or pulling down a pixel of the pixel array connected to one of the plurality of column lines currently selected by the column driver before the column driver selects a next column line.
15. The pixel driving circuit of claim 14 , wherein the row driver is further configured to provide the signal to pixels of the pixel array connected to the one of the plurality of column lines currently selected by the column driver in which an event has not occurred.
16. The pixel driving circuit of claim 11 , wherein the row driver comprises a shift register configured to select a respective one of the plurality of column lines.
17. The pixel driving circuit of claim 11 , wherein the controller is further configured to enable the global hold signal and the global reset signal to be in an inactive state.
18. A vision sensor comprising:
a pixel array including a plurality of pixels arranged in matrix form; and
a pixel driving circuit configured to detect whether an event has occurred in the plurality of respective pixels of the pixel array,
wherein each of the plurality of pixels includes:
a photoelectric device;
a current readout unit configured to detect an electric current flowing in the photoelectric device to generate an input voltage;
an event determination unit configured to determine an event occurrence and an event type, using the input voltage, and configured to output an event detection signal; and
an event output unit configured to store the event detection signal for an event-storage period, and configured to output the event detection signal stored in the event output unit.
19. The vision sensor of claim 18 , wherein the event output unit comprises:
a storage unit connected to an event output terminal and configured to store the event detection signal; and
a switch unit connected between the storage unit and an input terminal for the event detection signal.