Method for reducing shutter latency while maintaining low dark current in an imager and minimizing energy consumption
View Patent ↗A method for reducing shutter latency while maintaining low dark current in the imager and minimizing energy consumption in a digital camera, the method including the steps of providing an imager operating in accumulation mode; and substantially continuous flushing of charges from the imager before capturing an exposure of an image with a time between vertical transfers greater than or equal to time between vertical transfers during normal image readout so that, if continuous flushing for a time necessary to readout substantially all rows of pixels has occurred, the exposure may be captured with substantially zero latency.
1. A method for reducing shutter latency in an imager operating in accumulation mode, wherein the imager comprises an array of pixels arranged in rows and columns with two or more phases per pixel while maintaining low dark current in the imager and minimizing energy consumption, the method comprising the steps of:
(a) transferring excess charge from a row of pixels by setting one vertical clocking voltage operatively connected to one phase of the pixels in a row to a high level when another vertical clocking voltage operatively connected to another phase of the pixels in a row is at a low level and shifting the high level to a low level while shifting the low level to a high level;
(b) setting the vertical clocking voltages to a low level for a time duration selected to be between a minimum time duration that is greater than a time between row transfers during image readout and a maximum time duration of twice the time between row transfers during image readout; and
(c) repeating steps (a) and (b) for a time necessary to readout all rows of pixels such that an exposure may be captured with substantially zero latency.
2. The method as in claim 1 further comprising horizontal clocking having voltages that are substantially continuously low during the flushing for conserving energy.
3. The method as in claim 2 further comprising providing a horizontal flushing clocking which goes active immediately before capturing an exposure of the image for emptying charge from the horizontal register.
4. The method as in claim 1 further comprising fast flushing, in which the time between transfers of excess charge is minimum and precedes the continuous flushing.
5. A camera for reducing shutter latency while maintaining low dark current in the imager and minimizing energy consumption, the camera comprising:
(a) an imager operating in accumulation mode, wherein the imager comprises an array of pixels arranged in rows and columns with two or more phases per pixel; and
(b) two or more vertical clocking voltages each operatively connected to a phase of the pixels in a row and in which one vertical clocking voltage is at a high level when another vertical clocking voltage is at a low level and as the high level is shifted to a low level, the low level is shifted to a high level to transfer a row of excess charge, and after transferring a row of excess charge the two or more vertical clocking voltages are at a low level for a time duration selected to be between a minimum duration that is greater than a time between row transfers during image readout and a maximum duration that is twice the time duration between row transfers during image readout so that, if continuous flushing for a time necessary to readout all rows of pixels has occurred, the exposure may be captured with substantially zero latency.
6. The camera as in claim 5 further comprising horizontal clocking voltages that are substantially continuously low during the flushing for conserving energy.
7. The camera as in claim 6 further comprising horizontal clocking voltages which go active immediately before capturing an exposure of the image for emptying charge from the horizontal register.
8. The camera as in claim 5 further comprising fast flushing, in which the time between transfers of excess charge is minimum and precedes the continuous flushing.
9. The camera as in claim 5 wherein the imager comprises a two phase charge-coupled device imager.
10. The camera as in claim 9 wherein the time the vertical clocking voltages are high is substantially proportional to a square of a width of the two phase charge-coupled device imager.