Digital cameras use either a CCD or CMOS sensor. Although CCD sensors are capable of achieving high image quality, they have the disadvantage of slow data-reading speeds. CMOS sensors, on the other hand, offer high data-reading speeds, but are prone to noise, which affects image quality. Predicting from the very early stages that pixel counts and datareading rates for digital cameras would continually increase, Canon pursued research on CMOS sensors, accumulating wide-ranging technologies that eventually led to the development of high-quality CMOS sensors.

CMOS Sensor Technologies

The key to high photosensor performance is capturing as much light as possible while minimizing noise. Utilizing its micropatterning technology, Canon fabricated a microlens for each pixel, which measures only a few micrometers in size, for higher light intensity. The company also repeatedly improved its color filter, which is essential for color reproduction, to ensure enhanced color photosensor performance.

A high-sensitivity, low-noise photosensor is needed to obtain high-quality images from long exposures of starry night skies with a digital camera. This means reducing dark current to the lowest possible point. Canon improved the crystal structure of its silicon substrates and eliminated heavy metals (metal contamination) by employing various innovative manufacturing devices and by thoroughly controlling manufacturing processes, thereby reducing dark current as much as possible. Canon's photosensors offer the high sensitivity and high image quality required for astrophotography.

Photosensors collect electrical charges when exposed to light. The resulting charge is read out from each sensor site and converted into image data. For optimal device design, Canon simulates the ideal charge collection structure with a device simulator. This makes it possible to design a sensor with highly efficient charge collection, opto-electronic conversion, and reading over short periods of time.

Reducing noise in the photosensor is meaningless if the data-reading circuit is subject to high noise levels. Canon achieves low-noise data reading through a pixel configuration called the four-transistor pixel structure, and a noise cancellation circuit. In 2004, this technology received a National Commendation for Invention, Japan's most prestigious invention award. Recognized for its superiority, the circuit is now widely employed as the industry standard.

Double Sampling Noise Cancellation Method Used in CMOS Sensors

Canon's full-frame 35 mm CMOS sensor measures 36 x 24 mm, an area equal to a frame of traditional 35 mm film, which far exceeds the maximum area that can be covered in a single- exposure process using conventional semiconductor exposure equipment. Canon developed a multiple-exposure technology for its semiconductor exposure equipment enabling mass production of full-frame 35mm CMOS sensors.