Renesas Technical Solution: Optical Image Stabilizer (OIS) Platform

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Renesas Optical Image Stabilizer Driver IC.

Considerable attention has been drawn by the emerging use of optical image stabilization (OIS) for smartphone cameras. Conventional electronic Image Stabilizer consumes large quantities of memory and processor throughput, and is therefore a major challenge for smartphones. OIS, in contrast, works by adjusting the lens position itself, and is far less demanding on smartphone resources.

Renesas is now offering a full OIS platform comprising a high-performance dedicated LSI together with software and other required components—a solution that makes it much easier for smartphone makers to include OIS in their products. The platform's control firmware, stored in internal flash memory, can be easily modified to accommodate changes in product specifications and parameters, enabling automated tuning at time of manufacture—another considerable cost savings for manufacturers.

Today we hear from two engineers leading the OIS development effort—Masahiko Kashimura at Renesas Electronics, and Hirohide Okuno at Renesas Design.

Capabilities of the Renesas OIS LSI

Renesas OIS LSIs became available early in the first decade of the 2000s, and now enjoy wide use in digital still and digital video cameras. We subsequently began development of an OIS LSI—the R2A30515BM—designed specifically for smartphones, and our customers have already started shipping devices that include this new feature.

The R2A30515BM incorporates output-stage driver circuits, hall-element amplification, and many other peripheral analog circuits. It utilizes outstanding Renesas hardware: a dual processor (see Figure 1) comprising an ultra-low-power RL78 MCU and a custom-designed 32-bit "GREEN DSP" that delivers high speeds at low power.

Figure 1: System Block Diagram of the R2A30515BM Optical Image Stabilization LSI. The ultra-low-power processors—the RL78 and the

Figure 1: System Block Diagram of the R2A30515BM Optical Image Stabilization LSI. The ultra-low-power processors—the RL78 and the "GREEN DSP"—run on just 35 mW.

"The R2A30515BM hardware and its sophisticated algorithms together deliver superlative shake-reduction performance. While most OIS LSIs correct for shake angles only up to about 0.5 degree, the R2A30515BM corrects for angles up to 2 degrees. And because the DSP delivers high processing performance, it significantly reduces temperature drift from the gyro sensor, as well as actuator noise introduced when moving the lens or the imaging element. According to our data, actuator noise is more than 10 dB lower than that produced by a competitor's OIS LSI." (Okuno)

The following figures (Figs. 2, 3, 4) show Renesas test performance data for the R2A30515BM.

Figure 2: Vibration Tester Shakes the Camera (2 Hz to 10 Hz)

Figure 2: Vibration Tester Shakes the Camera (2 Hz to 10 Hz)

Figure 3: Blurring at 0.5° and 1.0° Vibration. OIS correction essentially eliminates the blurring seen in the upper row (where OIS was turned off).

Figure 3: Blurring at 0.5° and 1.0° Vibration. OIS correction essentially eliminates the blurring seen in the upper row (where OIS was turned off).

Figure 4: Blurring at 1.5° and 2.0° Vibration. Considerable blurring visible with OIS off (upper row); greatly reduced when OIS is on.

Figure 4: Blurring at 1.5° and 2.0° Vibration. Considerable blurring visible with OIS off (upper row); greatly reduced when OIS is on.

Figure 5: Renesas OIS LSI—Product Deployment

Figure 5: Renesas OIS LSI—Product Deployment

Customers are already shipping units equipped with our R2A30515BM, and end-users are taking note of the significant improvement over conventional electronic Image Stabilizer.

Supporting Freedom in Customer's Smartphone Design

The R2A30515BM—our first-generation OIS LSI—is already in mass production, with a number of different models with easy-customization. All models, of course, deliver high performance and low-power operation.

"For example, different makers and different models use different methods for driving the lens and imaging element. So we are careful that our LSI does not restrict the choice of drive method. Of course, we also provide software to meet the specific needs of each method." (Okuno)

"Another example is optical-path correction, where our LSI models support both the "lens barrel type" and "module tilt" methods for moving the imaging element. The two methods have different characteristics—as in differing corner distortion—and customers must have freedom in deciding which to use." (Okuno)

In addition to providing free choice of mechanical methods and drive methods, our LSIs also come with internal flash memory—so that they are self-sufficient in a way that competitor products are not. Data and CPU code are both stored in flash memory, eliminating the need to download these from system ROM every time power comes on. Processing can start immediately, using the code and data already held in the LSI.

Also, the RL78 side and the DSP side are both equipped with dedicated internal SRAM, eliminating the need to attach external EEPROM and allowing the OIS to be fully implemented using only a small number of parts.

The R2A30515BM chip size—inclusive of analog driver circuits, CPU, DSP, flash memory, and internal SRAM—is 2.7 х 2.9 mm, so that "it can be mounted as a typical chip component." (Kashimura)

Total Support―Full OIS platform

Our OIS is delivered in the form of a platform, within a comprehensive operational package. The package includes the LSI, corresponding algorithms (software), automatic tuning on customer's production line, and high-quality support from Renesas. In particular, automatic tuning on customer's production line can help reduce production costs and can "significantly enhance the customer's profit margin." (Kashimura)

An Advancing Technology: Future Development of the LSI

"We are now putting together the second generation LSI—the RAA305170GBM—with a renewed emphasis on flexibility. While the first generation R2A30515BM works only with PWM (pulse-width modulation) mechanical drive, the second generation will also support linear drive." (Okuno)

Because PWM operates at low power, it's suitable for smartphones having relatively limited power storage. But many manufacturers prefer linear drive, as the circuitry is easier to work with. Our new generation not only supports both methods, but allows them to be switched on-the-fly without interfering with autofocus and other operational settings. For example, PWM drive can be selected when shooting video, with linear drive selected when shooting stills.

We expect to see continuing demand for smartphones. Provided that today's smartphones are high-end products, in the future more and more products aimed at the popularization of smartphones will come into the market. They will probably have high pixel counts by the mature technology, and OISs that do not reduce the effective pixel count will mean a lot.

In addition, forthcoming OIS LSI models will also be suitable for sports (action) cameras. Today, many sportscams do not use any Image Stabilization, and almost all the rest use electronic image stabilization. As action cameras are subject to rather intense movement, however, we believe that they can make very effective use of optical Image Stabilization (OIS).

We should also note that while the technology we are discussing here has been designed to drive optical components so as to achieve image stability, it is probably quite suitable for controlling other movements as well. Kashimura stresses the importance of assessing customer requirements over a wide range of areas; and we, in turn, can expect to see broad use of the Renesas OIS series.

Figure 6: External appearance of RAA305170GBM chip

Figure 6: External appearance of RAA305170GBM chip