CMOS pioneer attacks CCD chip dominance

23 Nov 2004

From web-cams to high-end digital cameras, CMOS image sensors are now strongly challenging CCD technology. Oliver Graydon spoke to the Californian firm Omnivision Technologies, a pioneer in the field that has just released a 5 Megapixel CMOS sensor.

From Opto & Laser Europe December 2004

Riding the wave in demand for cheap image sensors for web-cams, mobile phones and toys, US firm Omnivision Technologies has propelled itself to the forefront of the digital imaging revolution that is now sweeping through households all over the world.

The origins of the Californian designer of CMOS image sensors date back to 1995 when Shaw Hong and Raymond Wu, two former Motorola engineers, saw the commercial potential for a cheap alternative to CCD sensors for low-end applications. They founded Omnivision with a clear goal: to make a sensor that would allow colour-PC video cameras (web-cams) to retail for just $99 (€76).

A few years later they succeeded, just as the market for multimedia applications exploded, and branched into the market for toys and consumer digital cameras. A highly successful initial public offering on the NASDAQ followed in 2000 and, today, the firm claims to be the largest independent maker of CMOS camera chips. "Our mission from the very beginning has been to focus on mass markets for low-cost digital imaging," said Jess Lee, director of product marketing for Omnivision. "Up to today, we have shipped over 90 million CMOS camera chips." The firm currently has a quarterly revenue of around $100 m and believes that there are many applications for its technology. Its sensors already appear in various portable products made by companies like Samsung, Motorola, Sony Ericsson and Siemens.

"The bulk of our revenue came from the digital camera space until the middle of last year, when the market for cellular phone cameras really took off," Lee told OLE. "The cellular phone market is huge; on a global basis, 610 million units are predicted to be shipped this year and about one-third of those are expected to be camera phones."

However, to describe Omnivision as a "maker" is slightly misleading as the firm is, in fact, a pure designer of chips and circuitry. It follows a "fabless" approach that sees it outsourcing all of its manufacturing. The well-known Taiwanese semiconductor fabs TSMC and Powerchip currently produce the silicon wafers that contain the firm's CMOS image sensors. These are then coated with glass and diced up ready for integration into a camera module complete with optics.

During its trading life, Omnivision has learned some hard lessons about running a rapidly expanding business, the most important of which was to avoid doing too much itself. "We started out as a pure silicon company and, for a period, when this market [mobile phone cameras] started taking off, we were making complete camera modules, but very quickly realized that we didn't want to be in that market," said Lee.

"We just weren't set up for it - we know how to design chips, but when it comes to logistics and managing a supply chain for connectors, plastic parts and lenses, it was a nightmare. We quickly realized that there were dozens of potential partners in the space we could team up with."

Another challenge that Omnivision has had to overcome is to hit the very low price points that are required for mass consumer markets. "For most toy applications, we need to make chips that don't go over the $1 mark," confirmed Lee. "It's extremely hard to hit this point and you need to make a lot of sacrifices. Performance is not anything like a CCD and the image size is usually very small."

Even for applications like mobile phones, a complete camera module only retails for a few dollars. "A VGA module retails for around $6-8 and is dropping quickly," Lee told OLE. "People are starting to talk about 1.3 and 2 Mpixel with autofocus, so the market is changing very quickly."

To keep pace with this demand, earlier this year Omnivision released two new image sensors especially for the camera-phone market: a 2 Mpixel sensor and the industry's smallest CMOS sensor - a 1/7-inch version with CIF (352 x 288) resolution.

As for technical reasons to embrace CMOS technology, Omnivision claims that it offers a number of advantages. For a start, the company says its imaging chip consumes significantly less power than a CCD chip and gives a more compact single-chip solution. Instead of requiring multiple chips to perform the analogue-to-digital conversion and digital signal processing of image signals generated from pixels, Omnivison says all of this functionality is contained within a single chip.

In effect, one CMOS chip features all of the camera-imaging functions such as automatic white balancing, exposure control, gain control, edge enhancement and colour processing. In theory, this makes it possible to construct smaller, simpler cameras, which can be highly attractive in portable applications such as mobile phones.

In August this year, Omnivision launched what it calls its "Omnipixel" technology, which it claims provides a light sensitivity, resolution, colour fidelity, and low noise comparable to high-quality CCD products. According to the firm, Omnipixel maximizes the sensor's fill factor (light sensitive area of the chip) while using a circuit structure that "virtually eliminates effects such as fixed pattern noise and dark current, ensuring consistently clear and sharp images".

To date, Omnipixel technology has been employed in two new sensors: a 3 Mpixel and a 5 Mpixel version that the firm hopes will displace CCD sensors in mid- and high-end digital cameras. However, there is no doubt that penetrating the market sector for consumer digital cameras will be difficult, as competition is extremely fierce.

Many of the leading Japanese digital camera-makers like Fuji, Konica, Nikon and Sony either already make their own CCD sensors or have a very long-standing and close relationship with domestic suppliers such as Sony, Toshiba and Matsushita. As a result, Omnivision's success probably lies with lesser-known camera-makers in Asia adopting the technology and rolling out products that are very price-competitive.

"CMOS is a tricky subject. It's turning out to be very good for cell phones, but it's not the answer for everything," commented Tom Hausken, an analyst at Strategies Unlimited who has written numerous reports on the topic. "It turns out that CMOS is good for high-end applications such as, for example, 16 Mpixel movie cameras, and the low end because of its low power-consumption. Contrastingly, in the middle range, CCDs are still doing very well. This is because it's hard to displace an entrenched technology and they deliver good performance."