ROHM Lens Drivers for Camera Modules
In recent years rapid advancements have been made in the smartphone camera landscape, with functions such as zoom, image stabilization, and autofocus becoming standard. Since 2008 ROHM has been developing lens driver ICs for camera modules, which are designed to be key devices for these additional functions and have been widely adopted both in Japan and abroad. Among these, in response to market demand for blur-free image capture of distant objects or under low-light conditions, we will focus on image optical image stabilization, which is expected to see increased adoption in the future.
ROHM Product Roadmap
Since it began offering autofocus lens driver ICs in 2008, ROHM has developed models that support actuators capable of bidirectional drive along with a ringing compensation function that suppresses transient oscillation for feed forward control which at the time was considered mainstream for autofocus lens drivers. In addition, ROHM is further expanding its lineup by developing lens drivers for feedback control type autofocus, models compatible with different ball-type actuators, and lens driver ICs for optical image stabilization that were first adopted in smartphones in 2012.
(Note) OIS: Optical Image Stabilization
Features of ROHM's Lens Drivers
■ Lens Drivers for Optical Image Stabilization
- Adopts robust, high performance servo design technology utilizing simulation (i.e. Matlab)
- Achieves lower power consumption through PWM drive
- Built-in module adjustment function improves yield and facilitates adjustment
■ Lens Driver for Feedback Autofocus
- Utilizes servo control technology optimized for phase difference auto focus (PDAF*)
- Temperature compensation of displacement detection results enabled based on temperature information
- Provides correction to improve the linearity between displacement detection signal and actual displacement
- *PDAF (Phase Detection Auto Focus)
- Unlike the contrast method that searches for the maximum point of contrast while moving the lens, phase detection involves dividing incoming light into pairs of images and comparing them using a dedicated sensor. This method detects the deviation in the direction of focus position from the distance between the 2 images, eliminating the need to search for the exact focus position as in the contrast method, making high-speed AF operation possible.
Optical vs electronic image stabilization
Electronic image stabilization basically detects image misalignment between frames and performs compensation accordingly. In contrast, with optical image stabilization camera shake/jitter signal is detected by a gyro sensor integrated in the smartphone or camera. Although both methods have their advantages and disadvantages, in recent years optical image stabilization has proven to be more effective in low light conditions and capturing subjects at longer distances, and as a result is expected to see increased adoption in the future. In addition, a number of cameras are starting to adopt hybrid systems utilizing both electronic and optical methods to improve image stabilization performance.
|Optical Image Stabilization
|Electronic image stabilization
|Requires space for drive mechanism and control IC
|Space required for optional separate IC for arithmetic operations
|Entire effective pixel area can be used
|Image area limited by margin required for image stabilization
|Image Quality Degradation due to
|Drive mechanism requires power
|Power required for arithmetic processing
Actuator mechanism for optical axis adjustment in optical image stabilization systems
Various methods to achieve optical image stabilization exist. In digital cameras the 'lens shift method', where only the compensation lens within the lens array shifts, and the 'sensor shift method' that involves shifting the image sensor element while the lens is fixed, are primarily used. Most cameras used in smartphones adopt the 'barrel shift method', in which the entire lens array is shifted. A number of actuators required for optical axis adjustment have been developed for these different systems. ROHM is also developing control technology for these actuators that is expected to improve camera module performance in the future.
In addition to lens drivers for camera modules, ROHM will continue to leverage the latest proprietary technologies and expertise to expand its industry-leading lineup and develop products that meet customer needs.