# How a Modern Camera Sensor Captures Light and Converts It to Data > This patent describes a camera sensor technology that combines light-capturing elements with a special circuit to read out the image data quickly and efficiently, all on a single chip. - **Patent:** US 5471515 - **Original title:** Active pixel sensor with intra-pixel charge transfer - **Owner:** California Institute of Technology - **Granted:** 1995 - **Status:** Public domain (expired) - **Times cited:** 620 - **Field:** consumer_electronics, semiconductors, telecommunications, automotive, software ## What it does The patent describes an imaging device, like a digital camera sensor, built on a single silicon chip using a common manufacturing process (CMOS). Each tiny picture element, or "pixel cell," has a photogate (Claim 1) that collects light and turns it into an electrical charge. This charge is then moved within the pixel by a small charge coupled device (CCD) section (Claim 1) to a sensing node. From there, a CMOS readout circuit (Claim 1) with an output field effect transistor (Claim 1) converts the charge into a voltage signal that can be read by the camera. For example, when light hits a pixel, the photogate gathers the light's energy, which is then quickly shifted by the CCD part to the readout circuit, allowing the camera to process the image. ## What it does NOT cover - Image sensors that use only traditional CCD technology for both charge collection and readout across the entire chip. - Sensors where the charge is read out directly from the photogate without an intermediate charge coupled device section within the pixel. - Image sensors that do not use a complementary metal oxide semiconductor (CMOS) circuit for the pixel's readout. - Sensors that rely on different charge accumulation mechanisms other than a photogate. - Pixel designs where the charge transfer and readout are handled by entirely separate, off-chip components. ## The clever bit The innovation was integrating a small, efficient charge transfer mechanism (a CCD section) within each pixel of a CMOS sensor, allowing for faster and lower-noise readout than previous CMOS designs, while still benefiting from the cost and integration advantages of CMOS manufacturing. ## Real-world examples 1. Smartphone camera sensors (e.g., Apple iPhone, Samsung Galaxy) 2. Digital single-lens reflex (DSLR) and mirrorless camera sensors 3. Webcams 4. Security cameras 5. Automotive cameras ## Why it matters This patent is foundational for the development of modern CMOS image sensors. These sensors became a key alternative to older CCD sensors, offering advantages in power consumption, manufacturing cost, and integration with other electronics. The technology enabled the widespread adoption of digital cameras in everything from smartphones to webcams and professional cameras. ## Frequently asked questions ### What does How a Modern Camera Sensor Captures Light and Converts It to Data cover? This patent describes a camera sensor technology that combines light-capturing elements with a special circuit to read out the image data quickly and efficiently, all on a single chip. ### Who owns patent US 5471515? California Institute of Technology owns this patent, granted in 1995. ### When does this patent expire? This patent has expired and is now in the public domain — anyone can use the invention freely. ### What is patent US 5471515 cited by? This patent has been cited by 620 later patents that build on its ideas. ### What problem does this patent solve? This patent is foundational for the development of modern CMOS image sensors. These sensors became a key alternative to older CCD sensors, offering advantages in power consumption, manufacturing cost, and integration with other electronics. The technology enabled the widespread adoption of digital cameras in everything from smartphones to webcams and professional cameras. ### What does this patent NOT cover? Image sensors that use only traditional CCD technology for both charge collection and readout across the entire chip. **Full plain-English explainer:** https://patentbrief.org/patent/us/5471515/cmos-active-pixel-image-sensor **Original patent:** https://patents.google.com/patent/US5471515 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Buried Channel CCDs Move Data Deep Inside Silicon Chips](https://patentbrief.org/patent/us/3792322/ccd-image-sensor) — A foundational 1974 invention that improved how computer chips store and move electrical charges by keeping them away from messy surface defects. - [The First Digital Camera's Core Technology](https://patentbrief.org/patent/us/4131919/digital-camera-electronic-still) — Kodak's 1978 patent on the fundamental technology for capturing, processing, and storing digital images using a CCD sensor and magnetic tape. - [How Touchscreens Precisely Align Signals to Detect Your Touch](https://patentbrief.org/patent/us/8493330/individual-channel-phase-delay-scheme) — Apple's patent describes a way for touchscreens to adjust the timing of internal electrical signals so they perfectly match the signals coming from your finger, making touch detection more accurate. - [How Flash Memory Cells Use an Erase Gate to Clear Data](https://patentbrief.org/patent/us/4531203/nand-flash-memory) — This 1985 patent describes the foundational structure of flash memory, introducing an 'erase gate' that allows data to be electrically wiped from a memory cell. - [How Robert Noyce Invented the Modern Integrated Circuit](https://patentbrief.org/patent/us/2981877/noyce-planar-integrated-circuit) — Robert Noyce's 1959 patent for a semiconductor device that uses evaporated metal leads to connect components directly on a single silicon chip.