Imaging apparatus with multiple local clocks for readout from a large number of photosensors
View Patent ↗In an imaging device having an array of photosensors, each photosensor being associated with a shift register stage for reading out image signals, there is provided a number of local clock drivers, each local clock driver being associated with a subset of photosensors. A reset flip-flop is associated with each subset of photosensors, and is used to “hand off” shift register activities from one local clock driver to the next as image data is read out. By having a series of local clock drivers, performance problems related to parasitic capacitance on the shift register lines are lessened.
1. A photosensitive apparatus, comprising at least one silicon chip, the silicon chip including:
a plurality of photosensors, organized in a plurality of subsets of photosensors, each photosensor having a shift register stage associated therewith, at least one photosensor in each subset outputting a signal to a common video line in response to the shift register stage associated therewith being activated;
a common shift register line for activating a plurality of shift register stages associated with a subset of photosensors; and
for each subset of photosensors, a local clock driver, the local clock driver including an enabling amplifier operatively disposed between the common shift register line and the shift register stages in the subset of photosensors, and a flip-flop associated with a first and last photosensor in the subset, the flip-flop outputting an enabling signal to the enabling amplifier.
2. The apparatus of claim 1 , further comprising
sequencing means for causing a second local clock driver to begin sequentially activating a plurality of shift register stages within its subset of photosensors, as a result of a first local clock driver finishing activating a plurality of shift register stages within its subset of photosensors.
3. The apparatus of claim 1 , the flip-flop in each local clock driver having a set input associated with a first shift register stage in the subset of photosensors, and a reset input associated with a last shift register stage in the subset of photosensors.
4. The apparatus of claim 1 , the last shift register stage associated with the first local clock driver being connected in series with a first shift register stage associated with the second local clock driver.
5. The apparatus of claim 1 , wherein a first subset of photosensors forms a first linear array of contiguous photosensors, and a second subset of photosensors forms a second linear array of contiguous photosensors.