US 5,471,515 · Granted 1995-11-28

The Caltech Patent That Invented Modern Camera Sensors

Imagine a tiny light detector smaller than a grain of salt that can grab photons and turn them into electrical signals fast enough for video. That's an active pixel sensor — and this 1995 patent describes how to cram thousands of them onto a single chip using standard manufacturing, which is why every smartphone camera works today.

Curated and verified by the IsItPatented Editorial team

The plain-English version

What it protects

The claim covers a monolithic imaging chip where each pixel cell contains a photogate (which collects light), a charge coupled device section (which moves the electrical charge around), and an output transistor (which reads the signal). What's protected here is the specific architecture of how these three components are integrated together on a single piece of silicon, and the method of transferring charge from the light-sensing area to the readout circuitry within each individual pixel.

Why it matters

This patent represents a foundational shift in how digital imaging works. Before active pixel sensors, cameras used passive pixel architectures that were slower and noisier. By putting the amplifier and readout transistor directly into each pixel cell, Caltech's design enabled faster, cleaner image capture at scales that could be manufactured affordably. This architecture became the backbone of nearly all digital cameras, smartphone sensors, and video devices that followed.

Real-world use

Every time you snap a photo on your phone or video chat with a friend, the camera sensor is using this pixel architecture — light hits the photogate, charge gets shuttled to the readout circuit, and the image appears on your screen in milliseconds.

Original USPTO abstract

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

Patent details

Publication number: US 5,471,515
Filing date: 1994-01-28
Grant date: 1995-11-28
Assignee: California Institute Of Technology
Inventor(s): FOSSUM; ERIC R., MENDIS; SUNETRA, KEMENY; SABRINA E.
CPC class: H10F39/1536

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