Bipolar junction transistor pixel circuit, driving method thereof, and image sensor

摘要

A bipolar junction transistor (BJT) pixel circuit, an image sensor and a driving method thereof are provided. The BJT pixel circuit includes a BJT, a photodetector, a feedback amplifier circuit, a shutter circuit, and a current generating unit. The photodetector generates a first base current to a base of the BJT responsive to a light incident on the photodetector. The feedback amplifier circuit is operative to increase an emitter voltage of the BJT according to the light intensity. The shutter circuit controls an exposure time of the photodetector according to a shutter signal. The current generating unit generates the second pulsed base current responsive to a trigger signal causing a base voltage of the BJT to drop while the feedback amplifier circuit operates to increase the emitter voltage of the BJT so as to build-up the base-emitter voltage to a predetermined voltage level when a light source turns on.

主权项

1. A bipolar junction transistor (BJT) pixel circuit, comprising:
a BJT transistor, a collector thereof coupled to a ground; a photodetector, having a first-end thereof coupled to a base of the BJT transistor, a second-end thereof coupled to the ground, the photodetector generating a first base current based on a light intensity of a light incident on the photodetector, wherein the light is illuminated from a light source; a feedback amplifier circuit, coupled to the base of the BJT transistor and an emitter of the BJT transistor, operative to increase an emitter voltage of the BJT transistor according to the light intensity; a shutter circuit, coupled to the feedback amplifier circuit, operative to control an exposure time of the photodetector according to a shutter signal; and a current generating unit, coupled to the base of the BJT transistor, generating a second pulsed base current to the base of the BJT transistor upon receiving a trigger signal; wherein the current generating unit generates the second pulsed base current responsive to the trigger signal causing a base voltage of the BJT transistor to drop while the feedback amplifier circuit operates to increase the emitter voltage of the BJT transistor so as to build up the base-emitter voltage to a predetermined voltage level when the light source turns on.