Image Sensor


Xerox has developed a Full Width Array (FWA) image sensor that is the best in its class for speed and image quality in traditional document scanning markets. This technology captures images reliably and accurately and will bring new levels of productivity and robustness to these applications. Xerox’s FWA technology enables high-speed black and white, color and infrared image capture while maintaining detailed resolution. Xerox is actively offering this sensor for use in print output integrity and inspection, machine vision and currency validation systems.

Technology Description

Xerox’s linear image sensors were developed in support of our digital copier and multifunction product lines. With twenty years of experience working in this arena, Xerox has developed a Full Width Array (FWA) CMOS image sensor technology that is the best in its class for speed and image quality in traditional document scanning markets.

The Xerox image sensor is made of several silicon CMOS sensor chips mounted together end-to-end with high precision, forming a seamless array of photosites over the length of the array. Xerox incorporates this technology in its products enabling scanning in widths ranging from 2 to 38 inches, at a resolution of 400 spi. These devices are monochrome (one single row of photosites) or color capable (three rows of photosites for RGB) or both (four rows). Scan speeds of 9 inches per second in full color are standard with higher speeds possible.

Xerox also has devices which are four row 600 spi chips and FWAs that run at speeds of 66 MHz per chip or channel of the FWA. This means that if all channels of a FWA (one chip per channel) of any length from .62 inch to 37.2 inchs or longer are used, the maximum monochrome scan rate is 248 ips (inches per second) or 82.7 ips for color, for full 8-12 bit (effective bits depend on illumination level) 600x600 spi output.

Special Features

Since these devices are collinear assemblies of chips, they can be made in any length from 0.62 inches to 37.2 inches in increments of 0.62 inches. Xerox also has the capability of placing infrared transmissive (visible blocking) filters on these sensors to enable infrared detection.

Xerox’s FWA technology enables the flexibility to add, modify or remove features as needed. For example, we can design the sensors for higher or lower resolutions, and/or change the shape of the photosites.

CMOS vs. CCD Technology

CMOS image sensors bring many advantages over the traditional CCDs. Xerox sensors consume less power than CCDs and require a lower voltage source to operate. The key advantage, however, is that CMOS sensors are produced in the same silicon wafer foundries that make devices for the computer and communication industries. This adds flexibility to the manufacturing options and takes advantage of the economy of scale associated with these very high-volume IC manufacturers. In contrast, CCD’s, require special fabrication processes that are only available from a handful of companies.

Applications / Industries

  • Currency recognition and validation systems for the beverage, vending and gaming industries
  • Machine vision systems for inspecting textiles, lumber, plastic webs and industrial parts
  • Print output inspection systems for monitoring the integrity of printed documents

Key Technical Specifications

Video Data Rate: The video data rate of each chip is of the order of 35 MHz (can vary from design to design). For example, a sensor made of 20 chips grouped in four channels of 5 chips may have a total data rate of 140 MHz.

Responsivity: The typical responsivity of a green photosite (@ 400spi) to green light is 150 V/mJ/cm2, which, when combined with the low noise level of the sensor, easily yields a signal to noise ratio significantly larger than 100:1 (typically 200 to 300) even when illuminated by a low power fluorescent lamp (~15W). By comparison, the reduction optics, single-chip CCD array used in the Xerox DocuImage 620S needs a 160W incandescent lamp to yield a comparable image quality.

Video Output: In the typical sensor shown, each sensor chip has its own video output. Therefore, a 20-chip sensor has 20 video outputs that can be flexibly combined into a single channel or up to 20 channels depending on the requirements. Alternatively, the sensor can be wired with a fixed number of channels. If required, all the chips can be connected serially with a single video output.

Power Requirements: Unlike CCD image sensors, that require a 12V power source, the CMOS image sensors used in our FWA’s only require 5.25V and in a typical application (five channels or less), consume less than 200 mA.

Nomenclature

FWA: An acronym for Full Width Array. This device is the width of the page to be scanned. It is sometimes referred to as a Page Width image sensor.

Multichip: The light sensitive elements in the Full Width Array imaging bars are arranged on discrete chips mounted end to end, each containing several hundred sensing units.

Collinear: The multichip device is collinear in the sense that the photosites form a seamless array of pixels in one single line over the full active length of the device, without being staggered.

Intellectual Property Summary

CMOS Sensor Chip Design - This group of patents relates to patents and know-how for chip level features that enhance the performance of the optical sensor as a stand-alone unit and as a building block for the multichip Full Width Array. Competitively advantaged performance characteristics include speed, linearity, responsivity, noise, cross talk, end pixel behavior, color fidelity, photoresponse uniformity and DC offset uniformity. Some of these design features are uniquely applicable to one-dimensional image sensor chips for use in collinear multichip arrays. Others could enhance any CMOS image sensor, one dimensional or two-dimensional.

Collinear Multichip Array Technology and Manufacturing - This group of patents relates to unique techniques needed to assemble and use the collinear multichip arrays. Typical technologies and processes include precision dicing and assembly, color filter technology, substrate materials, adhesives, rework and yield enhancement. Xerox technology is not specific to CMOS sensors, but covers techniques that could be used for the precision assembly of any multichip array, including CCD arrays or LED print bars.

Image Sensor Know-How - In addition to the published patents, there is a supporting body of know-how that is key to the successful fabrication of the Xerox image sensors. This know-how includes the following:
  • Tight integration and communication between the CMOS chip design team and the wafer foundry
  • Electro-optical testing of the wafers, chips and the finished arrays
  • Specialized equipment, tooling and processes used in the manufacturing line that produces the arrays that are unique to the assembly of these devices.
Backed by a substantial intellectual property base and an advanced manufacturing and production center, Xerox is actively licensing additional technologies and know-how relative to image sensing for various applications.

For Licensing Information

To learn more about licensing the Image Sensor technology.