The encyclopedia · Engineering & Operations · Technical decision · 1969–1975
Bell Labs' CCD turned light into charge that shuffles itself out of the chip
Boyle and Smith's 1969 charge-coupled device solved pixel readout by shifting electrons row by row like a bucket brigade, and became the digital camera's eye.
Bell Labs (AT&T)
The solution
In September 1969, Willard Boyle and George Smith sketched the charge-coupled device (CCD) on a blackboard at Bell Labs. They were chasing a better electronic memory for the lab's bubble-memory competition; as a memory it was soon forgotten, but the same mechanism became the basis of digital imaging.
The CCD's trick is how it reads out an image. Instead of wiring every photocell to its own amplifier, clocked voltages make the charge in each well slide into its neighbor — a bucket brigade — so an array of millions of pixels is drained through one serial register as a stream of electric signals.
By 1970 Boyle and Smith demonstrated a CCD in a video camera; Fairchild built the first 100x100-pixel image sensor in 1972, and the first camera with a built-in CCD reached the market in 1981. The pair shared half of the 2009 Nobel Prize in Physics for the invention, which the Nobel committee called the digital camera's 'electronic eye'.
Why it worked
- One serial read-out replaces an amplifier per pixel
- Charge packets scale with light intensity
- Solid-state imaging beat film and vacuum-tube cameras
- Mechanism transferred from memory research to imaging
What can be applied
If reading out millions of elements is the hard part, find a way to serialize the read: moving the data to one output beats wiring an output to every element.
Aftermath
The CCD enabled digital cameras, Hubble's deep-space images and medical imaging; CMOS sensors later displaced it in phones, but CCD remains the standard where sensitivity matters. Boyle and Smith received the 2009 Nobel Prize in Physics for the invention.
Sources
- The Nobel Prize in Physics 2009 — Press release
- The Nobel Prize in Physics 2009 — Popular information
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