BJT pixel circuit, image sensor including the same and operating method thereof
AssigneePixart Imaging Inc.
InventorWooi-Kip Lim
Life of this patent
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Abstract
There is provided an image sensor including a BJT pixel circuit and a light source. The BJT pixel circuit adopts a reset settling time of a base-emitter voltage of a bipolar junction transistor before the light source is turned on to illuminate light. The light source provides light energy to the BJT pixel circuit within a pre-flash time and an exposure time. The reset settling time, the pre-flash time and the exposure time are changed with light energy detected by the BJT pixel circuit with a negative relationship.
Claims20
A pixel circuit, comprising:
- a bipolar junction transistor, having a base and a collector;
- a reset transistor, connected between the base and the collector of the bipolar junction transistor, and configured to reset a base-emitter voltage of the bipolar junction transistor at a first time;
- and
- a photodiode, connected between the base and the collector of the bipolar junction transistor, and configured to receive pre-flash energy at a second time behind the first time to increase a beta of the bipolar junction transistor to a stable level,
- wherein a settling time between the first time and the second time is changed corresponding to light energy detected by the photodiode.
An image sensor, comprising:
- a light source;
- and
- multiple pixel circuits each comprising a bipolar junction transistor, a reset transistor and a photodiode, and each pixel circuit configured to
- in a first frame period, after a first settling time from resetting a base-emitter voltage of the bipolar junction transistor by the reset transistor, detect first pre-flash energy of the light source by the photodiode within a first pre-flash time to increase a beta of the bipolar junction transistor to a first stable level, and
- in a second frame period, after a second settling time from resetting the base-emitter voltage by the reset transistor, detect second pre-flash energy of the light source by the photodiode within a second pre-flash time to increase the beta of the bipolar junction transistor to a second stable level,
- wherein the first settling time is different from the second settling time, and the first pre-flash time is different from the second pre-flash time.
An operating method of an image sensor, the image sensor comprising a bipolar junction transistor (BJT) pixel circuit and a light source, the operating method comprising:
- resetting, using a base reset signal, a base-emitter voltage of a bipolar junction transistor of the BJT pixel circuit at a first time;
- and
- turning on, using a light source control signal, the light source for a pre-flash time at a second time to increase a beta of the bipolar junction transistor to a stable level,
- wherein the pre-flash time and a settling time of the base-emitter voltage between the first time and the second time are changed corresponding to light energy detected by the BJT pixel circuit.
Dependencies are inferred from the claim text.