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EP-4113978-B1 - IMAGE SENSOR INCLUDING PIXEL INCLUDING INTERNAL CAPACITOR

EP4113978B1EP 4113978 B1EP4113978 B1EP 4113978B1EP-4113978-B1

Inventors

  • JUNG, HYUNYONG
  • KIM, SEOKSAN
  • Seo, Minwoong
  • Chu, Myunglae

Dates

Publication Date
20260506
Application Date
20220506

Claims (5)

  1. An image sensor (10) comprising a plurality of pixels and a pixel driver (200), each of the plurality of pixels including: a photodetection circuit (110, 110a, 110b) configured to generate a detection signal (DS); and an analog-to-digital converter (120) configured to convert the detection signal (DS) using a ramp signal (RAMP), the analog-to-digital converter (120) including a first internal capacitor (C1), a second internal capacitor (C2) to which the ramp signal (RAMP) is applied, and a comparator (121) configured to compare the detection signal (DS) received through the first internal capacitor (C1) with the ramp signal (RAMP) received through the second internal capacitor (C2), and to output a comparison result signal (COUT), wherein the photodetection circuit (110, 110a, 110b) includes: a photodiode (PD); a floating diffusion node (FD) configured to accumulate photocharges generated by the photodiode (PD), the floating diffusion node (FD) including a parasitic capacitor (CFD); a transfer transistor (TX) configured to transmit the photocharges to the floating diffusion node (FD) in response to a transfer control signal output by the pixel driver; and an overflow transistor (SOF) having a first terminal coupled to the floating diffusion node (FD) and a second terminal coupled to the first internal capacitor (C1), wherein in accordance with an overflow control signal (OFS) provided to the overflow transistor (SOF), the floating diffusion node (FD) electrically connects to the first internal capacitor (C1), wherein the overflow transistor (SOF) is configured to electrically connect the floating diffusion node (FD) to an output node (NO) of the photodetection circuit (110), or electrically isolate the floating diffusion node (FD) from the output node (NO), in response to the overflow control signal (OFS) output by the pixel driver (200) to the overflow transistor (SOF), wherein the first internal capacitor (C1) with a capacitance is connected to the output node (NO), wherein when the overflow transistor (SOF) is turned on, the floating diffusion node (FD) is connected to the output node (NO), and thus, the parasitic capacitor (CFD) of the floating diffusion node (FD) is electrically connected to the first internal capacitor (C1) such that the equivalent capacitance of the floating diffusion node (FD) increases, and photocharges generated by the photodiode (PD) are accumulated in the parasitic capacitor (CFD) of the floating diffusion node (FD) and the first internal capacitor (C1).
  2. The image sensor (10) as claimed in claim 1, wherein: the photodetection circuit (110, 110a, 110b) further includes a source follower (SF) configured to amplify a voltage change of the floating diffusion node (FD), and to output the amplified voltage change to the output node (NO), and the overflow transistor (SOF) is connected between the floating diffusion node (FD) and the output node (NO).
  3. The image sensor (10) as claimed in claim 1, wherein: the photodetection circuit (110, 110a, 110b) includes: a source follower (SF) configured to amplify a voltage change of the floating diffusion node (FD), and to output the amplified voltage change to the output node (NO); a reset transistor (RX) configured to reset the floating diffusion node (FD) to a power supply voltage (VDD); and a conversion gain transistor (DCGX) connected between a reset node (NR) and the floating diffusion node (FD), the reset node (NR) is connected to one terminal of the reset transistor (RX), and the overflow transistor (SOF) is connected between the reset node (NR) and the output node (NO).
  4. The image sensor (10) as claimed in claim 1, wherein: the photodetection circuit (110, 110a, 110b) further includes a selection transistor (SX) connected to the output node (NO) from which the detection signal (DS) is output, and the selection transistor (SX) is turned off in a period in which the overflow transistor (SOF) is turned on.
  5. The image sensor (10) as claimed in claim 1, configured to operate in each of a plurality of modes according to illuminance, wherein: the plurality of modes includes an overflow operation mode and a high conversion gain, HCG, mode, and when the image sensor (10) operates in the overflow operation mode, the pixel driver (200) generates the overflow control signal (OFS) such that the photocharges generated by the photodetection circuit (110, 110a, 110b) are stored in the internal capacitor (C1), and when the image sensor (10) operates in the HCG mode, the pixel driver (200) generates the overflow control signal (OFS) such that the floating diffusion node (FD) of the photodetection circuit (110, 110a, 110b), in which the photocharges are accumulated, is electrically isolated from the internal capacitor (C1).

Description

BACKGROUND 1. Field Embodiments relate to an image sensor, and more particularly, to an image sensor including a pixel having an internal capacitor. 2. Description of the Related Art An image sensor may be a device configured to capture two-dimensional (2D) or three-dimensional (3D) images of an object. The image sensor may generate an image of the object using a photoelectric conversion element configured to respond to the intensity of light reflected from the object. In recent years, with the development of the computer industry and the communication industry, the demand for image sensors with improved performance has increased in various electronic devices, such as digital cameras, camcorders, personal communication systems (PCSs), game consoles, security cameras, medical micro cameras, and mobile phones. EP 3 681 147 A1 relates to a solid-state imaging device, a method for driving a solid-state imaging device, and an electronic apparatus. US 2009/086071 A1 discloses: A pixel includes a photodiode, an overflow circuit, a first sensing circuit, and a second sensing circuit. The first sensing circuit charges and discharges a cathode capacitance by a photocurrent flowing through a photodiode, and amplifies an obtained voltage by a source follower amplifier so as to be outputted to a data line. The second sensing circuit charges and discharged the cathode capacitance by the photocurrent flowing through the photodiode, and outputs electric charge stored in the cathode capacitance via the data line. A pixel circuit is configured so that a first mode in which the first sensing circuit becomes active and a second mode in which the second sensing circuit becomes active can be switched. The first mode and the second mode are switched according to an amount of light received by the photodiode included in each pixel circuit. Gain is controlled according to the amount of light received, in the first mode, and the storage time is controlled in the second mode. US 2019/098232 A1 discloses: A solid-state imaging device, in which a signal holding part can hold a signal with respect to a voltage signal corresponding to an accumulated charge in a photoelectric conversion element of a photodiode which is transferred to an output node of a floating diffusion in a transfer period after an integration period and a signal with respect to a voltage signal corresponding to an overflow charge overflowing to the output node of the floating diffusion from at least the photodiode in any period among the photoelectric conversion element of the photodiode and the storage capacity element of the storage capacitor. US 2020/195870 A1 discloses: An image sensor includes a pixel that includes a photoelectric conversion element converting an incident light to an electrical signal, a switch adjusting a capacitance of a floating diffusion (FD) node at which charges corresponding to the electrical signal are stored, and a readout circuit outputting an output voltage based on the FD node. An A/D converter may sample the output voltage transferred from the readout circuit through an output line respectively at a first time and a second time and generate a digital code based on a difference therebetween. A conversion gain controller may generate a conversion gain control signal by comparing the output voltage transferred from the readout circuit through the output line with a threshold voltage at a third time between the first and second times and provide the conversion gain control signal to the switch to set conversion gain of the pixel. SUMMARY Embodiments of the invention are defined in the appended claims. According to the invention, there is provided an image sensor as set out in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Features will become apparent to those of skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which: FIG. 1 is a block diagram of an image sensor according to an example embodiment;FIG. 2 is a circuit diagram of a portion of a pixel included in an image sensor according to an example embodiment;FIG. 3 is a timing diagram of control signals and a ramp signal, which are provided to a pixel included in an image sensor, according to an example embodiment;FIG. 4 is a diagram of a potential level of a pixel in a sampling period during an overflow operation;FIG. 5 is a circuit diagram of a portion of a pixel included in an image sensor according to an example embodiment;FIG. 6 is a circuit diagram of a portion of a pixel included in an image sensor according to an example embodiment;FIG. 7 is a block diagram of an image sensor according to an example embodiment;FIGS. 8 and 9 are circuit diagrams of pixels included in image sensors, according to example embodiments;FIGS. 10 and 11 are circuit diagrams of pixels included in image sensors, according to example embodiments;FIG. 12 is a block diagram of an electronic device including a multi-camera module, according to an example em