Active pixel sensor - Wikipedia. An active- pixel sensor (APS) is an image sensor consisting of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. There are many types of active pixel sensors including the complementary metal–oxide–semiconductor (CMOS) APS used most commonly in cell phone cameras, web cameras, most digital pocket cameras since 2. DSLRs). Such an image sensor is produced using CMOS technology (and is hence also known as a CMOS sensor), and has emerged as an alternative to charge- coupled device (CCD) image sensors. The term active pixel sensor is also used to refer to the individual pixel sensor itself, as opposed to the image sensor; [1] in that case the image sensor is sometimes called an active pixel sensor imager,[2] or active- pixel image sensor.[3]History[edit]The term active pixel sensor was coined in 1. Tsutomu Nakamura who worked on the Charge Modulation Device active pixel sensor at Olympus,[4] and more broadly defined by Eric Fossum in a 1. Image sensor elements with in- pixel amplifiers were described by Noble in 1. Welcome to Asset Store. Asset Store is home to thousands of assets that will accelerate your development in Unity. To get you started, we hand-picked 12 of the best. Chamberlain in 1. Weimer et al. in 1. The MOS passive- pixel sensor used just a simple switch in the pixel to read out the photodiode integrated charge.[9] Pixels were arrayed in a two- dimensional structure, with an access enable wire shared by pixels in the same row, and output wire shared by column. At the end of each column was an amplifier. Passive- pixel sensors suffered from many limitations, such as high noise, slow readout, and lack of scalability. The addition of an amplifier to each pixel addressed these problems, and resulted in the creation of the active- pixel sensor. Noble in 1. 96. 8 and Chamberlain in 1. MOS readout amplifiers per pixel, in essentially the modern three- transistor configuration. The CCD was invented in October 1. Bell Labs. Because the MOS process was so variable and MOS transistors had characteristics that changed over time (Vth instability), the CCD's charge- domain operation was more manufacturable and quickly eclipsed MOS passive and active pixel sensors. A low- resolution "mostly digital" N- channel MOSFET imager with intra- pixel amplification, for an optical mouse application, was demonstrated in 1. Another type of active pixel sensor is the hybrid infrared focal plane array (IRFPA) designed to operate at cryogenic temperatures in the infrared spectrum. The devices are two chips that are put together like a sandwich: one chip contains detector elements made in In. Ga. As or Hg. Cd. Te, and the other chip is typically made of silicon and is used to read out the photodetectors. The exact date of origin of these devices is classified, but by the mid- 1. Download free test patterns and cross-patform freeware for monitor calibration. Imaging Associates provide color management solutions to digital photographers and.Facebook is testing a snooze function that mutes a page for a certain period, rather than forever. This would be even more useful on Twitter, where usually lovely. By the late 1. 98. CMOS process was well established as a well controlled stable process and was the baseline process for almost all logic and microprocessors. There was a resurgence in the use of passive- pixel sensors for low- end imaging applications,[1. However, CCDs continued to have much lower temporal noise and fixed- pattern noise and were the dominant technology for consumer applications such as camcorders as well as for broadcast cameras, where they were displacing video camera tubes. Eric Fossum, et al., invented the image sensor that used intra- pixel charge transfer along with an in- pixel amplifier to achieve true correlated double sampling (CDS) and low temporal noise operation, and on- chip circuits for fixed- pattern noise reduction, and published the first extensive article[5] predicting the emergence of APS imagers as the commercial successor of CCDs. Between 1. 99. 3 and 1. Jet Propulsion Laboratory developed a number of prototype devices, which validated the key features of the technology. Though primitive, these devices demonstrated good image performance with high readout speed and low power consumption. In 1. 99. 5, personnel from JPL founded Photobit Corp., who continued to develop and commercialize APS technology for a number of applications, such as web cams, high speed and motion capture cameras, digital radiography, endoscopy (pill) cameras, DSLRs and camera- phones. Many other small image sensor companies also sprang to life shortly thereafter due to the accessibility of the CMOS process and all quickly adopted the active pixel sensor approach. Most recent, the CMOS sensor technology has spread to medium- format photography with Phase One being the first to launch a medium format digital back with a Sony- built CMOS sensor. Comparison to CCDs[edit]APS pixels solve the speed and scalability issues of the passive- pixel sensor. They generally consume less power than CCDs, have less image lag, and require less specialized manufacturing facilities. Unlike CCDs, APS sensors can combine the image sensor function and image processing functions within the same integrated circuit. APS sensors have found markets in many consumer applications, especially camera phones. They have also been used in other fields including digital radiography, military ultra high speed image acquisition, security cameras, and optical mice. Manufacturers include Aptina Imaging (independent spinout from Micron Technology, who purchased Photobit in 2. Canon, Samsung, STMicroelectronics, Toshiba, Omni. Vision Technologies, Sony, and Foveon, among others. CMOS- type APS sensors are typically suited to applications in which packaging, power management, and on- chip processing are important. CMOS type sensors are widely used, from high- end digital photography down to mobile- phone cameras. Advantages of CMOS compared with CCD[edit]A big advantage of a CMOS sensor is that it is typically less expensive than a CCD sensor. A CMOS sensor also typically has better control of blooming (that is, of bleeding of photo- charge from an over- exposed pixel into other nearby pixels). Disadvantages of CMOS compared with CCD[edit]. Distortion caused by a rolling shutter. Since a CMOS sensor typically captures a row at a time within approximately 1/6. For example, when tracking a car moving at high speed, the car will not be distorted but the background will appear to be tilted. A frame- transfer CCD sensor or "global shutter" CMOS sensor does not have this problem, instead captures the entire image at once into a frame store. The active circuitry in CMOS pixels takes some area on the surface which is not light- sensitive, reducing the quantum efficiency of the device. Back- illuminated sensors can mitigate this problem. Architecture[edit]. A three- transistor active pixel sensor. The standard CMOS APS pixel today consists of a photodetector (a pinnedphotodiode[1. T cell.[1. 4] The pinned photodiode was originally used in interline transfer CCDs due to its low dark current and good blue response, and when coupled with the transfer gate, allows complete charge transfer from the pinned photodiode to the floating diffusion (which is further connected to the gate of the read- out transistor) eliminating lag. The use of intrapixel charge transfer can offer lower noise by enabling the use of correlated double sampling (CDS). The Noble 3. T pixel is still sometimes used since the fabrication requirements are less complex. The 3. T pixel comprises the same elements as the 4. T pixel except the transfer gate and the photodiode. The reset transistor, Mrst, acts as a switch to reset the floating diffusion to VRST, which in this case is represented as the gate of the Msf transistor. When the reset transistor is turned on, the photodiode is effectively connected to the power supply, VRST, clearing all integrated charge. Since the reset transistor is n- type, the pixel operates in soft reset. The read- out transistor, Msf, acts as a buffer (specifically, a source follower), an amplifier which allows the pixel voltage to be observed without removing the accumulated charge. Its power supply, VDD, is typically tied to the power supply of the reset transistor VRST. The select transistor, Msel, allows a single row of the pixel array to be read by the read- out electronics. Other innovations of the pixels such as 5. T and 6. T pixels also exist. By adding extra transistors, functions such as global shutter, as opposed to the more common rolling shutter, are possible. In order to increase the pixel densities, shared- row, four- ways and eight- ways shared read out, and other architectures can be employed. A variant of the 3. T active pixel is the Foveon X3 sensor invented by Dick Merrill. Verizon Says It Was Totally Just Testing How to Throttle Video. After rumors spread on Reddit that Verizon Wireless customers were unable to achieve feeds of faster than 1. Mbps while connected to Netflix, the company confirmed to Ars Technica this week it was conducting “network testing over the past few days to optimize the performance of video applications on our network.”While both Ars Technica and The Verge were able to confirm Verizon Wireless seemed to be capping Netflix speeds at somewhere between 5. Mbps and 1. 0Mbps, the apparent throttling would not necessarily affect most users. On mobile, Netflix should have functioned fine for most users other than those streaming high quality video over a tethered connection. Some users reported similar throttling of You. Tube video, though again at a 1. Mbps rate which allowed high quality streaming. Just a few months ago, Verizon claimed its new unlimited data plan wouldn’t throttle video — at least until users hit 2. GB of data. For its part, the company told Ars Technica the video throttling was “across the board” and affected its own video streaming services, not just third- party services. However, with FCC Chairman Ajit Pai seemingly dead- set on strangling net neutrality to death, Verizon might soon get an opportunity to test many new and exciting forms of data throttling on its customers.[Ars Technica].
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