CMOS sensors are not necessarily better than traditional CCD technology

When you look at the most recent introductions of camcorders, it’s clear that CMOS imaging technology is on the rise. Sony, Canon, Ikegami and Thomson Grass Valley have all announced CMOS sensors in their latest camcorders, while Panasonic and JVC continue to use CCD.
Take, for example, Sony’s new PMW-EX1 XDCAM EX, which uses half-inch “Exmore” CMOS sensors, or the company’s HVR-A1U model, based on a one-third-inch CMOS imager with Enhanced Imaging Processor (EIP).

Sony said its latest CMOS technology has smaller transistors within the image’s pixel matrix, which allows a larger area to be photo-sensitive. This enables more light to be taken in than with a conventional CMOS sensor.

To achieve wider dynamic range, Sony’s EIP technology uses an algorithm that separates image data into its texture patterns and brightness components. In addition, something called Correlated Double Sampling circuits on the sensor help achieve “extremely low-noise” image quality.

Sony also claims that its new camcorders run at lower voltage and consume less power than devices using conventional CCD-based processors, resulting in longer battery life and using smaller batteries.

While CMOS sensors have dominated the news, many DPs will tell you that this does not mean they are better than more traditional CCD technology. CMOS manufacturing has caught up to CCD, which used to require very specific fabrication technology.

Dalsa, a company that makes both types of sensors, says that within a CCD sensor, every pixel’s charge is transferred through a very limited number of output nodes to be converted to voltage, buffered, and sent off-chip as an analog signal.

In a CMOS sensor, each pixel has its own charge-to-voltage conversion, and the sensor often also includes amplifiers, noise-correction, and digitization circuits, so that the chip outputs digital bits.

At the end of the day, there is little difference in operational quality. It might depend more on the cost of the component to each manufacturer.

To read more about the difference between CCD and CMOS sensors, visit www.dalsa.com/markets/ccd_vs_cmos.asp