Image sensor having pixels in linear mode and photovoltaic mode
In a case where a photodiode is in a saturated state, the photodiode can be transited from the saturated state to an unsaturated state during a period when a knee pulse is supplied from a knee pulse supplying unit. The knee pulse supplying unit preferably supplies the knee pulse a plurality of times during one frame period.
1. An image sensor including a plurality of pixels, wherein
each of the pixels includes:
a photodiode configured to operate in a linear mode in which the photodiode shows a linear response to incident light and also in a photovoltaic mode in which the photodiode shows a logarithmic response to the incident light,
a reset transistor configured to reset the photodiode,
a peak hold circuit configured to integrate an output of the photodiode, wherein the peak hold circuit includes: (1) a peak hold transistor configured to receive an output of the photodiode at a gate, (2) a switch transistor configured to turn on/off an output of the peak hold transistor, and (3) a holding capacitor configured to accumulate an output of the switch transistor, and
a knee pulse supplying unit connected to an output end of the photodiode through a knee capacitor and configured to supply a knee pulse for shifting a voltage at the output end of the photodiode for a predetermined period, and
in a case where the photodiode is in a saturated state, the photodiode is transited from the saturated state to an unsaturated state during a period when the knee pulse is supplied from the knee pulse supplying unit.
2. The image sensor according to claim 1 , wherein the knee pulse supplying unit supplies the knee pulse a multiple times during one frame period.
3. The image sensor according to claim 1 , wherein the knee pulse supplying unit supplies the knee pulse 30 times to 300 times during one frame period.
4. The image sensor according to claim 1 , wherein the knee pulse is a two-step pulse changed in a stepwise manner.
5. The image sensor according to claim 1 , further comprising:
a vertical scan circuit;
a plurality of analog-to-digital converters; and
a horizontal scan circuit, wherein
the plurality of pixels are arranged in a matrix,
the vertical scan circuit sequentially selects and drives, in a vertical direction, the plurality of pixels arranged in a horizontal direction,
the analog-to-digital converter converts signals from the plurality of pixels selected by the vertical scan circuit into a plurality of digital signals, and
the horizontal scan circuit serially outputs the plurality of digital signals.
6. The image sensor according to claim 5 , wherein the knee pulse supplying unit supplies the knee pulse a multiple times during one frame period.
7. The image sensor according to claim 5 , wherein the knee pulse supplying unit supplies the knee pulse 30 times to 300 times during one frame period.
8. The image sensor according to claim 5 , wherein the knee pulse is a two-step pulse changed in a stepwise manner.