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.
Original patent title: “Active pixel sensor with intra-pixel charge transfer”
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. Granted to California Institute of Technology in 1995 with 21 claims and 620 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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 (ClaimclaimA numbered sentence at the end of a patent that legally defines what the inventor owns. The most important section.Read more → 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.
The gap
What does this patent 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.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
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.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Smartphone camera sensors (e.g., Apple iPhone, Samsung Galaxy)
Digital single-lens reflex (DSLR) and mirrorless camera sensors
Webcams
Security cameras
Automotive cameras
Why it matters
The bigger picture
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.
Filed
January 28, 1994
Granted
November 28, 1995
Market context
Who's building on this
Companies in this space
The original assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →, California Institute of Technology, licensed this technology. Companies like Sony, Samsung, Omnivision, and Canon are major players in the CMOS image sensor market, continuously developing and improving upon the fundamental principles laid out in patents like this one. Many startups also leverage advanced CMOS sensor designs for specialized applications like medical imaging or autonomous vehicles.
Market impact
This patent helped pave the way for the widespread adoption of CMOS image sensors, which eventually surpassed traditional CCD sensors in many applications due to their lower power consumption, smaller size, and lower manufacturing costs. It enabled the integration of high-quality cameras into mobile phones and other portable devices, creating entirely new product categories and significantly expanding the digital imaging market.
Claim 1 — Plain English
What this patent covers
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.
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.
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.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Strong
Citation count
40/40
Highly cited
Claim breadth
14/20
Broad claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
20/20
Major company or institution
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$82K – $262K
Midpoint $164K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
The original legal language
Original claims
21 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Fossum, E. R., Kemeny, S. E., & Mendis, S. (1995). How a Modern Camera Sensor Captures Light and Converts It to Data (U.S. Patent No. 5,471,515). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/5471515/cmos-active-pixel-image-sensor
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
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.
Same assignee
More from California Institute of Technology
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