Wireless Systems Design

Camera Phones Shift Into Auto-Focus

Since the arrival of camera phones, consumers have shown a clear interest in these devices and—more importantly—a willingness to buy them. Now, cell-phone makers are excitedly touting the improved resolution of the next wave of camera phones. Consumers will certainly enjoy being able to take, send, and print higher-resolution photos. If some industry experts are correct, improved camera phones could eventually phase out digital cameras. Yet such sweeping success can only be guaranteed if camera phones can match the functionality of digital cameras.

Some companies are already working on adding such features to cell-phone cameras. Through a strategic partnership, for example, Atsana Semiconductor (www.atsana.com) and 1 (www.1limited.com) plan to make auto-focus functionality available to manufacturers of mobile feature phones. Usually, camera-enabled mobile phones rely on fixed-focus lenses. These lenses fail to provide the same image quality as digital still cameras and camcorders. One issue is that the depth of field is short. Because of production-line tolerance issues, focus quality also can vary from camera to camera.

With higher-resolution megapixel cameras, these problems worsen. Due to the smaller pixel pitch of these cameras, the depth of field grows shorter. In addition, production-line tolerance issues become more noticeable. Clearly, auto-focus mechanisms are critical to such cameras.

Conventional auto-focus mechanisms, which use electromagnetic transducers, exhibit several limitations when they're used in mobile phones. Their mechanical motors are expensive, large in size, and hungry for power. In contrast, the Helimorph actuator from 1 has a patented helical structure that provides a compact, low-power solution. The actuator is made out of a piezoelectric ceramic material, which changes shape when a voltage is applied across it. That change is extremely small—typically a few tens of microns. The Helimorph's geometry mechanically amplifies these minor changes, thereby providing displacement for a compact actuator.

This auto-focus solution consists of the camera module with 1's Helimorph actuator interfaced directly to Atsana's J2211 media processor (SEE FIGURE). The solution is controlled through an I2C interface. The auto-focus algorithm, which runs on the J2211 media processor, can provide reliable and high-speed auto-focus functionality. The J2211 also performs all of the ISP functions as well as JPEG image and MPEG-4 video processing. For users, this technology merger results in much higher image quality. For manufacturers, however, it could reveal a host of new application areas.

By combining a piezoelectric actuator with a media processor, two companies are bringing auto-focus with increased programmability to cell-phone cameras.

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