# US 12,764,438 B2 · BJT pixel circuit, image sensor including the same and operating method thereof > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,764,438 B2 - Document ID: US12764438B2 - Status: Granted - Kind: B2 - Application number: 19/054,921 - Filed: 2025-02-17 - Published: 2026-08-20 - Granted: 2026-10-13 - Earliest claimed: 2025-02-17 - Assignees: Pixart Imaging Inc. - Applicants: Pixart Imaging Inc. - Inventors: Wooi-Kip Lim - Web page: https://patentgrep.com/patent/US12764438B2 ## CPC - H04N 25/771: comprising storage means other than floating diffusion - H04N 23/71: Circuitry for evaluating the brightness variation - H04N 23/73: by influencing the exposure time - H04N 23/74: by influencing the scene brightness using illuminating means - H04N 25/53: Control of the integration time - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## 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. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) The pixel circuit as claimed in claim 1, further comprising a feedback amplifier circuit configured to establish the base-emitter voltage during a pre-flash time that the photodiode is receiving the pre-flash energy to increase the beta to the stable level, wherein the pre-flash time is changed with the changing of the settling time with a positive relationship. ### Claim 3 (depends on 1) The pixel circuit as claimed in claim 1, further comprising: a storage capacitor, configured to record pixel data of the pixel circuit; and a shutter circuit, configured to trigger an exposure time of the pixel circuit at a third time behind the second time to discharge the storage capacitor. ### Claim 4 (depends on 3) The pixel circuit as claimed in claim 3, wherein the exposure time is changed with the changing of the settling time with a positive relationship. ### Claim 5 (depends on 1) The pixel circuit as claimed in claim 1, wherein the light energy is detected by the photodiode of the pixel circuit within an exposure time of a previous image frame. ### Claim 6 (depends on 5) The pixel circuit as claimed in claim 5, wherein the settling time is shorter when the light energy in the previous image frame is stronger, and the settling time is longer when the light energy in the previous image frame is weaker. ### Claim 7 (depends on 6) The pixel circuit as claimed in claim 6, wherein in the previous frame, the pixel circuit uses a default settling time, which is longer than the settling time. ### Claim 8 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. ### Claim 9 (depends on 8) The image sensor as claimed in claim 8, wherein when the first settling time is longer than the second settling time, the first pre-flash time is longer than the second pre-flash time, and when the first settling time is shorter than the second settling time, the first pre-flash time is shorter than the second pre-flash time. ### Claim 10 (depends on 8) The image sensor as claimed in claim 8, wherein the each pixel circuit is further configured to in the first frame period, detect first light energy of the light source by the photodiode within a first exposure time, and in the second frame period, detect second light energy of the light source by the photodiode within a second exposure time. ### Claim 11 (depends on 10) The image sensor as claimed in claim 10, wherein when the first settling time is longer than the second settling time, the first exposure time is longer than the second exposure time, and when the first settling time is shorter than the second settling time, the first exposure time is shorter than the second exposure time. ### Claim 12 (depends on 10) The image sensor as claimed in claim 10, wherein the first frame period is prior to the second frame period, and the second settling time is determined according to the first light energy. ### Claim 13 (depends on 12) The image sensor as claimed in claim 12, further comprising: a memory, configured to record a relationship between multiple predetermined light energy zones and multiple predetermined settling times; and a processor, configured to determine the second settling time according to the relationship. ### Claim 14 (depends on 8) The image sensor as claimed in claim 8, wherein the each pixel circuit is further configured to in an initial frame period, after a default settling time from resetting the base-emitter voltage by the reset transistor, detect pre-flash energy of the light source by the photodiode within a default pre-flash time to increase the beta of the bipolar junction transistor to a stable level, and the default settling time is longer than the first settling time, and the default pre-flash time is longer than the first pre-flash time. ### Claim 15 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. ### Claim 16 (depends on 15) The operating method as claimed in claim 15, wherein the BJT pixel circuit further comprises a shutter circuit and a storage capacitor, and the operating method further comprises: triggering an exposure time of the BJT pixel circuit by the shutter circuit at a third time to discharge the storage capacitor, wherein the exposure time is changed with the changing of the settling time with a positive relationship. ### Claim 17 (depends on 15) The operating method as claimed in claim 15, wherein the light energy is detected by the BJT pixel circuit in an exposure time of a previous image frame. ### Claim 18 (depends on 17) The operating method as claimed in claim 17, wherein the settling time and the pre-flash time are shorter when the light energy in the previous image frame is stronger, and the settling time and the pre-flash time are longer when the light energy in the previous image frame is weaker. ### Claim 19 (depends on 17) The operating method as claimed in claim 17, wherein in the previous image frame, the BJT pixel circuit uses a default settling time of the base-emitter voltage, and the default settling time is longer than the settling time. ### Claim 20 (depends on 15) The operating method as claimed in claim 15, further comprising: changing the settling time according to the light energy in a step manner.