Less than five years ago, there was a battle raging between two camera sensor technologies, CCD and CMOS. Many thought CMOS was on the losing end as CCD boasted higher image quality. But since CMOS used less power and were far less expensive to produce, manufacturers pushed to advance CMOS sensor technology and their popularity exploded.
1. Back-lit and Front-lit Illumination
Back-side illumination offered an exciting alternative in CMOS sensor design. By putting the photodiode and substrate between the lens and wiring, manufacturers were able to improve sensitivity, signal-to-noise ratios, and dynamic range. The design also reduces complexity and build costs for CMOS sensors.
Back-lit illumination performance is boosted in high-speed applications with the use of global shutters. Global shutters expose all the sensor’s pixels to an image at the same time. Although rolling shutter sensors are less expensive to produce, they leave artifacts when imaging fast-moving objects. Global shutters boost the viability of CMOS sensors in added applications.
2. Sensor Size Goes Up, Pixel Size Goes Down
Imaging applications have become more demanding and CMOS technology has been pushed to increase image capture quality and resolution. CMOS sensor manufacturers had to develop a design that would increase resolution without increasing sensor noise. To accomplish this, they decreased pixel size and slightly increased sensor size to add more pixels to the sensor.
To accommodate the larger pixel and sensor sizes, lens manufacturers had to make changes to the optics. New lens designs added additional optical elements to take advantage of the larger CMOS sensors, making them heavier. Lens designers have created new mounts such as the TFL and TFL-II for added stability, support for the heavier lenses, and improved alignment.
3. Microlenses Gather More Light
CMOS pixels have a light-sensitive area and a light-insensitive amplifier area. Modern CMOS sensors now have microlenses to optimize this construction. These microlenses are placed above each CMOS cell. The lens directs light onto the light-sensitive part of the pixel. This lets manufacturers increase pixel sensitivity and decrease pixel noise.
Adding microlenses does have a drawback. Incident light must come in at a certain angular range. Any light outside the range can result in a shading effect on the pixel. Improvements in lens technology help to ensure that light comes at an ideal angle and minimize shading, are yet another example of how lens technology has risen to support CMOS tech.
Find the right CMOS sensor solution for your vision system with help from the experts at Phase 1 Technology.