CMOS Digital Image Sensors

CMOS Digital Image Sensors

Adding vision to your projects needs not be a difficult task. Whether its machine vision for robot control or the sampling and storage of images for security, CMOS images sensors can offer many advantages over traditional CCD sensors. Just some of the technical advantages of CMOS sensors are,

No Blooming Low power consumption. Ideal for battery operated devices Direct digital output (Incorporates ADC and associated circuitry) Small size and little support circuitry. Often just a crystal and some decoupling is all that is needed. Simple to design with.

There are many manufacturers making CMOS Image Sensors. Just some of the more notable ones are Micron who acquired Photobit, OmniVision, ST who acquired VLSI Vision, Mitsubishi and Kodak.

There are two different categories of CMOS Sensors based on their output. One type will have a analog signal out encoded in a video format such as PAL, NTSC, S-Video etc which are designed for camera on a chip applications. With these devices you simply supply power and feed the output straight into you AV Equipment. Others will have a digital out, typically a 4/8 or 16 bit data bus. These 'digital' sensors simplify designs, where once a traditional 'analog' camera was feed into a video capture card for conversion to digital. Today, digital data can be pulled straight from the sensor.

The main components to a Digital Video Camera design are

• CMOS Image Sensor. The heart of the camera. It produces a digital/analog output representing each pixel. It's support circuitry will normally include a Crystal Oscillator and power supply decoupling. Some sensors may need a resistive bias network of some type. All of these components are normally surface mounted on the back of the PCB and occupies very little real estate.
• The lens Holder. This will be either a plastic or metal mount which attaches to your PCB and allows a standard size lens to be screwed in. The screw thread facilitates focusing for fixed lens systems. The base of the lens mount may also have a IR (Infra Red) filter.
• The Lens. This will determine your Field of view among other things. Lenses range from fish-eye to telescopic and need to be purchased to fit the parameters of your sensor and lens holder.