Time of flight imaging using long and short-exposure storage nodes
Examples are disclosed that relate to time of flight imaging using long-exposure and short-exposure storage nodes for each pixel tap of a pixel in an image sensor. One example provides a time-of-flight camera, comprising an image sensor comprising a plurality of pixels, each pixel of the plurality of pixels comprising one or more taps, each tap comprising a photogate, a short-exposure storage node configured to receive charge during a short-exposure interval of an integration period, a long-exposure storage node configured to receive charge during a long-exposure interval of the integration period, a short-exposure switch gate configured to direct charge generated during the short-exposure interval to the short-exposure storage node, a long-exposure switch gate configured to direct charge generated during the long-exposure period to the long-exposure storage node, and a readout mechanism comprising one or more floating diffusion capacitors.
1. A time-of-flight camera, comprising:
a global shutter image sensor comprising a plurality of pixels, each pixel of the plurality of pixels comprising one or more taps, each tap comprising
a photogate,
a short-exposure storage node configured to receive charge during a short-exposure interval of an integration period,
a long-exposure storage node configured to receive charge during a long-exposure interval of the integration period,
a short-exposure switch gate in series with the photogate, the short-exposure switch gate configured to direct charge generated during the short-exposure interval to the short-exposure storage node,
a long-exposure switch gate in series with the photogate and in parallel with the short-exposure switch gate, the long-exposure switch gate configured to direct charge generated during the long-exposure period to the long-exposure storage node, and
a readout mechanism comprising one or more floating diffusion (FD) capacitors.
2. The time-of-flight camera of claim 1 , wherein the one or more taps comprises a first tap and a second tap, and wherein the readout mechanism comprises
a short-exposure FD capacitor configured to receive charge from the short-exposure storage node of the first tap and to receive charge from the short-exposure storage node of the second tap, and a long-exposure FD capacitor configured to receive charge from the long-exposure storage node of the first tap and to receive charge from the long exposure storage node of the second tap.
3. The time-of-flight camera of claim 1 , wherein the readout mechanism comprises, for each tap, a long-exposure FD capacitor and a short-exposure FD capacitor.
4. The time-of-flight camera of claim 1 , wherein the readout mechanism comprises, for each tap, a shared FD capacitor configured to receive charge from the short-exposure storage node and from the long-exposure storage node of the tap.
5. The time-of-flight camera of claim 4 , further comprising a controller configured to selectively readout charge from the short-exposure storage node and charge from the long-exposure storage node in sequence in a high dynamic range mode, and readout a sum of the charge from the short-exposure storage node and the charge from the long-exposure storage node in a non-high dynamic range mode.
6. The time-of-flight camera of claim 1 , wherein the readout mechanism comprises instructions executable to utilize a readout of the long-exposure storage node as a signal for the pixel when the long-exposure storage node is not saturated, and to utilize a readout of the short-exposure storage node multiplied by a ratio of the long-exposure interval to the short-exposure interval as the signal for the pixel when the long-exposure storage node is saturated.
7. The time-of-flight camera of claim 1 , wherein the ratio of the long-exposure interval to the short-exposure interval is variable.
8. The time-of-flight camera of claim 1 , further comprising an anti-blooming gate.
9. The time-of-flight camera of claim 1 , wherein each of the short-exposure storage node and the long-exposure storage node comprises one or more of a storage capacitor or a storage diode.
10. A method of operating a time-of-flight camera, the method comprising:
integrating a plurality of pixels via a global shutter during an integration period comprising a short-exposure interval and a long-exposure interval, each pixel of the plurality of pixels comprising one or more taps;
for each tap,
directing charge generated during the short-exposure interval to a short-exposure storage node via a short-exposure switch gate, and
directing charge generated during the long-exposure interval to a long-exposure storage node via a long-exposure switch gate; and
during a readout period,
reading out charge stored on the short-exposure storage node and charge stored on the long-exposure storage node via one or more floating diffusion (FD) capacitors.
11. The method of claim 10 , wherein reading out charge comprises, for each tap, reading out charge via a short-exposure FD capacitor for the short-exposure storage node, and reading charge via a long-exposure FD capacitor for the long-exposure storage node.
12. The method of claim 10 , wherein
reading out the charge stored on the short-exposure storage node comprises reading out the charge stored on a short-exposure storage node of a first tap and charge stored on a short-exposure storage node of a second tap using a short-exposure FD capacitor shared by the first tap and the second tap, and
reading out the charge stored on the long-exposure storage node comprises reading out the charge stored on a long-exposure storage node of the first tap and charge stored on a long-exposure storage node of the second tap using a long-exposure FD capacitor shared by the first tap and the second tap.
13. The method of claim 10 , wherein reading charge comprises, for each tap, reading charge at a FD capacitor shared by the short-exposure storage node and the long-exposure storage node for the tap.
14. The method of claim 13 , further comprising selectively reading out charge from the short-exposure storage node and charge from the long-exposure storage node in sequence in a high dynamic range mode, and reading out a sum of the charge from the short-exposure storage node and the charge from the long-exposure storage node in a non-high dynamic range mode.
15. The method of claim 10 , further comprising utilizing a readout of the long-exposure storage node as a signal for the pixel when the long-exposure storage node is not saturated, and utilizing a readout of the short-exposure storage node multiplied by a ratio of the long-exposure interval to the short-exposure interval as the signal for the pixel when the long-exposure storage node is saturated.
16. A time-of-flight camera, comprising:
a global shutter image sensor comprising a plurality of pixels, each pixel of the plurality of pixels comprising
one or more taps, each tap comprising
a photogate,
a short-exposure storage node configured to receive charge during a short-exposure interval of an integration period,
a long-exposure storage node configured to receive charge during a long-exposure interval of the integration period,
a short-exposure switch gate configured to direct charge generated during the short-exposure interval to the short-exposure storage node,
a long-exposure switch gate configured to direct charge generated during the long-exposure interval to the long-exposure storage node,
a readout mechanism comprising one or more floating diffusion (FD) capacitors, and instructions executable to
determine a long-exposure signal and a short-exposure signal,
if the long-exposure signal is not saturated, read out the long-exposure signal as a pixel signal, and
if the long-exposure signal is saturated, read out the short-exposure signal multiplied by a ratio of the long-exposure interval to the short-exposure interval as the pixel signal.
17. The time-of-flight camera of claim 16 , wherein the one or more taps comprises a first tap and a second tap, and wherein the readout mechanism comprises
a short-exposure FD capacitor configured to receive charge from a short-exposure storage node of the first tap and to receive charge from a short-exposure storage node of the second tap, and a long-exposure FD capacitor configured to receive charge from a long-exposure storage node of the first tap and a long exposure storage node of the second tap.
18. The time-of-flight camera of claim 16 , wherein the readout mechanism comprises, for each tap, a long-exposure FD capacitor; and a short-exposure FD capacitor.
19. The time-of-flight camera of claim 16 , wherein the readout mechanism comprises, for each tap, a shared FD capacitor configured to receive charge from the short-exposure storage node and from the long-exposure storage node.
20. The time-of-flight camera of claim 19 , further comprising a controller configured to selectively readout charge from the short-exposure storage node and charge from the long-exposure storage node in sequence in a high dynamic range mode, and readout a sum of the charge from the short-exposure storage node and the charge from the long-exposure storage node in a non-high dynamic range mode.