Choosing a CMOS Image Sensor for Camera Systems

When it comes to sensors for precision imaging systems, you have three ideal choices: microbolometer, charge-coupled detector (CCD), and CMOS image sensor modules. Bolometer-based systems are ideal for precision infrared imaging, while CCD and CMOS image sensor modules are ideal for color or monochrome imaging. Each of these can be used to capture high quality images, although they have different ideal applications and advantages.

If you are designing a new product for consumer-level or industrial imaging, and you’ll manufacture at high volume, a CMOS image sensor is probably the best choice. Let’s take a look at what you need to know to select a high-quality CMOS image sensor for use in your next imaging system.

Choosing a CCD vs. CMOS Image Sensor

CCDs CMOS image sensors come in color and monochrome varieties, and each type of image sensor is quite different. CCD imaging sensors generally have higher sensitivity and with lower noise compared to a CMOS image sensor with the same pixel size and density. CCD image sensors are often Peltier-cooled in scientific applications and extremely low luminosity applications, which reduces noise in the image and provides very high resolution. CCDs also tend to cost more because they are produced at lower volume than CMOS image sensors, simply because most applications do not require the level of precision provided by a CCD.

Contrast this with CMOS image sensors, which are produced using the same process as CMOS ICs (hence the name). These devices cost less and tend to use less power, but they also produce images with more noise and lower resolution. CMOS sensors do provide faster electro-optic conversion, so they can be used in video applications with high frame rate. The noise in a CMOS image sensor can be removed from the captured image using filtering and averaging. This makes CMOS-sensors ideal for consumer electronics applications, including IoT and mobile devices.

Functional block diagram for a CMOS image sensor

If you’re looking for a CMOS image sensor for a video or camera module in your next product, here are some points to consider:

• Resolution. This is the most widely cited performance metric for CCD and CMOS image sensors. Just like display modules, these devices have some specified resolution and pixel pitch. Resolution refers to the number of pixels, but the real factor that determines image quality is pixel pitch (normally specified in units of distance). A CMOS image sensor with a smaller pixel pitch will have finer resolution. When combined with pixel pitch and pixel number, you can determine the field of view for images gathered with your system. Note that resolution is sometimes quoted in megapixels (MP). As a reference, the newest, most advanced smartphones contain ~7 MP image sensors.
• Backside illumination. A back-side illuminated (BSI) CMOS sensor has higher sensitivity thanks to changes in the pixel architecture. These sensors are currently used in the newest generations of smartphones and in camera systems that must operate in low-light conditions.
• Mounting to your PCB. A CMOS image sensor will typically mount to a PCB as an SMD or through-hole component. Some CMOS sensors come as a die that mounts to a BGA.
• Integration. Some CMOS image sensors come packaged as a system-on-chip (SoC) and are integrated with their signal processing block.
• Temperature stability. Compared to CCD sensors, CMOS sensors have higher noise figure. Note that the noise level increases with temperature.
• Infrared filtering. Some CMOS image sensors include a thin film of material that absorbs or reflects infrared light. You should check for the presence of an infrared filter on your CMOS image sensor.
• Dynamic range. Like other sensors, this defines the input light intensity range over which a module can provide images without reaching saturation.

CMOS Image Sensor Units for Different Applications

If you look through the market, you’ll see that different CMOS image sensor units provide a broad range of resolutions. Certain applications don’t require a 10 MP camera, as we will see below.

Omnivision Technologies OV02686-H38A

The OV02686-H38A CMOS image sensor from Omnivision is ideal for budget smartphones, tablets, laptop webcams, or other devices that are not necessarily intended for capturing extremely fine images. This 1600 x 1200 pixel module provides 10-bit RGB color images (1 billion unique colors) at 15 frames per second. The pixel size is 1.75 microns, providing high resolution images with large field of view. The image sense core includes an integrated ADC, giving the module a small footprint.

Omnivision OV02686-H38A integrated CMOS image sensor module block diagram. From the OV02686-H38A product brief.

Micron MT9V022IA7ATC

The MT9V022IA7ATC color CMOS image sensor has 752 x 480 pixels in a 52-pin IBGA package. This product is marketed for automotive applications. Although it does not have the same resolution as typical image sensors used in smartphones, it offers an impressive 100 dB dynamic range. This module also provides a number of standard signal processing functions with an integrated controller. Some applications in the automotive sector include driver drowsiness detection, biometrics, and collision avoidance.

Image quality from the MT9V022IA7ATC CMOS image sensor at different temperatures. From the MT9V022IA7ATC product brief.

ON Semiconductor MT9F002I12STCV-DP

If you’re looking for serious image quality for a professional camera, the MT9F002I12STCV-DP is ideal for capturing images and video with 4608 x 3288 pixel resolution (that’s 15 MP!). This color CMOS image sensor can also gather images in 4:3 or 16:9 aspect ratios. This particular CMOS image sensor provides sensitivity and SNR that are competitive with CCDs at 13 frames per second. An integrated ADC provides 12-bit color depth with data provided in serial or parallel:

The MT9F002 is a progressive-scan sensor that generates a stream of pixel data at a constant frame rate. It uses an on-chip, phase-locked loop (PLL) to generate all internal clocks from a single master input clock running between 2 and 64 MHz. The maximum output pixel rate is 220 Mp/s for serial HiSPi I/F and 96 Mp/s for parallel I/F, corresponding to a pixel clock rate of 220 MHz and 96 MHz, respectively. [Source: MT9F002I12STCV-DP datasheet]

Still image and HD video capture modes. From the MT9F002I12STCV-DP datasheet.

Whether you’re building professional-grade cameras, smartphones, or other devices that require image sensing, Octopart gives you access to a massive range of CMOS image sensor units and controllers for use in your new product. Try using our Part Selector guide to determine the best option for your next product.

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