CMOSimage sensor working principle

Both CMOS and CCD imagers are constructed from silicon. This gives them fundamentally similar properties of sensitivity over the visible and near-IR spectrum. Thus, both technologies convert incident light (photons) into electronic charge (electrons) by the same photoconversion process.  Both technologies can support two flavors of photo element - the photogate and the photodiode. Generally, photodiode sensors are more sensitive, especially to blue light, and this can be important in making color cameras. ST makes only photodiode-based CMOS image sensors.Color sensors can be made in the same way with both technologies; normally by coating each individual pixel with a filter color (e.g. red, green, blue).

The following information will concentrate on the regions in which cellular and other services operate, currently from about 600 MHz to 3700 MHz. Propagation at these frequencies (see Figure 3) is best accomplished over an unobstructed visual line-of-sight (LOS) path between transmitter and receiver, as attenuation and changes in signal characteristics are minimal. LOS is an ideal condition for a wireless transmission because the propagation challenge comes only from weather or atmospheric parameters and the characteristics of its operating frequency. Consequently, the transmission path can be longer and signal strength higher, resulting in greater throughput.

CMOS Cameraprice

VISION's 800 x 1000 color sensor provides high resolution at lower cost than comparable CCDs. Image courtesy of VISION. Passive- and Active-pixel sensors There are two basic kinds of CMOS image sensors—passive and active. Passive-pixel sensors (PPS) were the first image-sensor devices used in the 1960s. In passive-pixel CMOS sensors, a photosite converts photons into an electrical charge. This charge is then carried off the sensor and amplified. These sensors are small—just large enough for the photosites and their connections. The problem with these sensors is noise that appears as a background pattern in the image. To cancel out this noise, sensors often use additional processing steps. Active-pixel sensors (APSs) reduce the noise associated with passive-pixel sensors. Circuitry at each pixel determines what its noise level is and cancels it out. It is this active circuitry that gives the active-pixel device its name. The performance of this technology is comparable to many charge-coupled devices (CCDs) and also allows for a larger image array and higher resolution. Inexpensive CMOS chips are being used in low-end digital cameras. There is a consensus that while these devices may dominate the low-end of the camera market, more expensive active-pixel sensors will become dominant in niches.   Toshiba Corporation fabricates a 1,300,000 pixel complementary metal oxide semiconductor (CMOS) image sensor. Courtesy of Toshiba. CMOS image sensor facts Here are some things you might like to know about CMOS image sensors: CMOS image sensors can incorporate other circuits on the same chip, eliminating the many separate chips required for a CCD. This also allows additional on-chip features to be added at little extra cost. These features include anti-jitter (image stabilization) and image compression. Not only does this make the camera smaller, lighter, and cheaper; it also requires less power so batteries last longer.   It is technically feasible but not economic to use the CCD manufacturing process to integrate other camera functions, such as the clock drivers, timing logic, and signal processing on the same chip as the photosites. These are normally put on separate chips so CCD cameras contain several chips, often as many as 8, and not fewer than 3. CMOS image sensors can switch modes on the fly between still photography and video. However, video generates huge files so initially these cameras will have to be tethered to the mothership (the PC) when used in this mode for all but a few seconds of video. However, this mode works well for video conferencing although the cameras can't capture the 20 frames a second needed for full-motion video. While CMOS sensors excel in the capture of outdoor pictures on sunny days, they suffer in low light conditions. Their sensitivity to light is decreased because part of each photosite is covered with circuitry that filters out noise and performs other functions. The percentage of a pixel devoted to collecting light is called the pixel’s fill factor. CCDs have a 100% fill factor but CMOS cameras have much less. The lower the fill factor, the less sensitive the sensor is and the longer exposure times must be. Too low a fill factor makes indoor photography without a flash virtually impossible. To compensate for lower fill-factors, micro-lenses can be added to each pixel to gather light from the insensitive portions of the pixel and "focus" it down to the photosite. In addition, the circuitry can be reduced so it doesn't cover as large an area.   Fill factor refers to the percentage of a photosite that is sensitive to light. If circuits cover 25% of each photosite, the sensor is said to have a fill factor of 75%. The higher the fill factor, the more sensitive the sensor. Courtesy of Photobit. CMOS sensors have a higher noise level than CCDs so the processing time between pictures is higher as these sensors use digital signal processing (DSP) to reduce or eliminate the noise. The DSP is one early camera (the Svmini), executes 600,000,000 instructions per picture. IMAGE SIZES The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

Here are some things you might like to know about CMOS image sensors: CMOS image sensors can incorporate other circuits on the same chip, eliminating the many separate chips required for a CCD. This also allows additional on-chip features to be added at little extra cost. These features include anti-jitter (image stabilization) and image compression. Not only does this make the camera smaller, lighter, and cheaper; it also requires less power so batteries last longer.   It is technically feasible but not economic to use the CCD manufacturing process to integrate other camera functions, such as the clock drivers, timing logic, and signal processing on the same chip as the photosites. These are normally put on separate chips so CCD cameras contain several chips, often as many as 8, and not fewer than 3. CMOS image sensors can switch modes on the fly between still photography and video. However, video generates huge files so initially these cameras will have to be tethered to the mothership (the PC) when used in this mode for all but a few seconds of video. However, this mode works well for video conferencing although the cameras can't capture the 20 frames a second needed for full-motion video. While CMOS sensors excel in the capture of outdoor pictures on sunny days, they suffer in low light conditions. Their sensitivity to light is decreased because part of each photosite is covered with circuitry that filters out noise and performs other functions. The percentage of a pixel devoted to collecting light is called the pixel’s fill factor. CCDs have a 100% fill factor but CMOS cameras have much less. The lower the fill factor, the less sensitive the sensor is and the longer exposure times must be. Too low a fill factor makes indoor photography without a flash virtually impossible. To compensate for lower fill-factors, micro-lenses can be added to each pixel to gather light from the insensitive portions of the pixel and "focus" it down to the photosite. In addition, the circuitry can be reduced so it doesn't cover as large an area.   Fill factor refers to the percentage of a photosite that is sensitive to light. If circuits cover 25% of each photosite, the sensor is said to have a fill factor of 75%. The higher the fill factor, the more sensitive the sensor. Courtesy of Photobit. CMOS sensors have a higher noise level than CCDs so the processing time between pictures is higher as these sensors use digital signal processing (DSP) to reduce or eliminate the noise. The DSP is one early camera (the Svmini), executes 600,000,000 instructions per picture. IMAGE SIZES The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

Although slant polarization should theoretically cause a 3-dB (half-power) reduction in link budget caused by polarization mismatch, multipath propagation has the effect of restoring it because polarization is no longer purely horizontal/vertical and at a ±45-degree slant. The result is typically only about a 1-dB reduction in link budget.

CMOSfull form

CCD vs. CMOS IMAGE SENSORS Until recently, CCDs were the only image sensors used in digital cameras. Over the years they have been well developed through their use in astronomical telescopes, scanners, and video camcorders. However, there is a new challenger on the horizon, the CMOS image sensor that may eventually play a significant role in some parts of the market. Let's compare these two devices.

Slant polarization appears to be able to withstand the effects of fading caused by reflections better than horizontal/vertical polarization, and some sources cite its ability to reduce interference where there are many simultaneous emitters. Finally, received signals typically appear at the receiving end more vertically than horizontally polarized, creating an unequal relationship, as vertical polarization often delivers a stronger signal than its horizontal counterpart at the receive location. Slant polarization can minimize this issue by equalizing the signal levels from both orientations.

Figure 1. The basic orientation of electromagnetic waves, whose polarization is either horizontal or vertical in relation to the Earth’s surface.

Figure 3. Three main signal propagation environments, including near line of sight. The Fresnel zone is the volume within which signals are diffracted from solid objects in their path.

There are two basic kinds of CMOS image sensors—passive and active. Passive-pixel sensors (PPS) were the first image-sensor devices used in the 1960s. In passive-pixel CMOS sensors, a photosite converts photons into an electrical charge. This charge is then carried off the sensor and amplified. These sensors are small—just large enough for the photosites and their connections. The problem with these sensors is noise that appears as a background pattern in the image. To cancel out this noise, sensors often use additional processing steps. Active-pixel sensors (APSs) reduce the noise associated with passive-pixel sensors. Circuitry at each pixel determines what its noise level is and cancels it out. It is this active circuitry that gives the active-pixel device its name. The performance of this technology is comparable to many charge-coupled devices (CCDs) and also allows for a larger image array and higher resolution. Inexpensive CMOS chips are being used in low-end digital cameras. There is a consensus that while these devices may dominate the low-end of the camera market, more expensive active-pixel sensors will become dominant in niches.   Toshiba Corporation fabricates a 1,300,000 pixel complementary metal oxide semiconductor (CMOS) image sensor. Courtesy of Toshiba. CMOS image sensor facts Here are some things you might like to know about CMOS image sensors: CMOS image sensors can incorporate other circuits on the same chip, eliminating the many separate chips required for a CCD. This also allows additional on-chip features to be added at little extra cost. These features include anti-jitter (image stabilization) and image compression. Not only does this make the camera smaller, lighter, and cheaper; it also requires less power so batteries last longer.   It is technically feasible but not economic to use the CCD manufacturing process to integrate other camera functions, such as the clock drivers, timing logic, and signal processing on the same chip as the photosites. These are normally put on separate chips so CCD cameras contain several chips, often as many as 8, and not fewer than 3. CMOS image sensors can switch modes on the fly between still photography and video. However, video generates huge files so initially these cameras will have to be tethered to the mothership (the PC) when used in this mode for all but a few seconds of video. However, this mode works well for video conferencing although the cameras can't capture the 20 frames a second needed for full-motion video. While CMOS sensors excel in the capture of outdoor pictures on sunny days, they suffer in low light conditions. Their sensitivity to light is decreased because part of each photosite is covered with circuitry that filters out noise and performs other functions. The percentage of a pixel devoted to collecting light is called the pixel’s fill factor. CCDs have a 100% fill factor but CMOS cameras have much less. The lower the fill factor, the less sensitive the sensor is and the longer exposure times must be. Too low a fill factor makes indoor photography without a flash virtually impossible. To compensate for lower fill-factors, micro-lenses can be added to each pixel to gather light from the insensitive portions of the pixel and "focus" it down to the photosite. In addition, the circuitry can be reduced so it doesn't cover as large an area.   Fill factor refers to the percentage of a photosite that is sensitive to light. If circuits cover 25% of each photosite, the sensor is said to have a fill factor of 75%. The higher the fill factor, the more sensitive the sensor. Courtesy of Photobit. CMOS sensors have a higher noise level than CCDs so the processing time between pictures is higher as these sensors use digital signal processing (DSP) to reduce or eliminate the noise. The DSP is one early camera (the Svmini), executes 600,000,000 instructions per picture. IMAGE SIZES The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

Inexpensive CMOS chips are being used in low-end digital cameras. There is a consensus that while these devices may dominate the low-end of the camera market, more expensive active-pixel sensors will become dominant in niches.

CCD technology is now about 25 years old. Using a specialised VLSI process, a very closely packed mesh of polysilicon electrodes is formed on the surface of the chip. These are so small and close that the individual packets of electrons can be kept intact whilst they are physically moved from the position where light was detected, across the surface of the chip, to an output amplifier. To achieve this, the mesh of electrodes is clocked by an off-chip source. It is technically feasible but not economic to use the CCD process to integrate other camera functions, like the clockdrivers, timing logic, signal processing, etc. These are therefore normally implemented in secondary chips. Thus most CCD cameras comprise several chips, often as many as 8, and not fewer than 3.  Apart from the need to integrate the other camera electronics in a separate chip, the achilles heel of all CCD's is the clock requirement. The clock amplitude and shape are critical to successful operation. Generating correctly sized and shaped clocks is normally the function of a specialised clock driver chip, and leads to two major disadvantages; multiple non-standard supply voltages and high power consumption. It is not uncommon for CCD's to require 5 or 6 different supplies at critical and obscure values. If the user is offered a simple single voltage supply input, then several regulators will be employed internally to generate these supply requirements.  On the plus side, CCD's have matured to provide excellent image quality with low noise.CCD processes are generally captive to the major manufacturers. History The CCD was actually born for the wrong reason. In the 1960s there were computers but the inexpensive mass-produced memory they needed to operate (and which we take for granted) did not yet exist. Instead, there were lots of strange and unusual ways being explored to store data while it was being manipulated. One form actually used the phosphor coating on the screen of a display monitor and wrote data to the screen with one beam of light and read it back with another. However, at the time the most commonly used technology was bubble memory. At Bell Labs (where bubble memory had been invented), they then came up with the CCD as a way to store data in 1969. Two Bell Labs scientists, Willard Boyle and George Smith, "started batting ideas around," in Smith's words, "and invented charge-coupled devices in an hour. Yes, it was unusual—like a light bulb going on." Since then, that "light bulb" has reached far and wide. Here are some highlights: In 1974, the first imaging CCD was produced by Fairchild Electronics with a format of 100x100 pixels. In 1975,the first CCD TV cameras were ready for use in commercial broadcasts. In 1975, the first CCD flatbed scanner was introduced by Kurzweil Computer Products using the first CCD integrated chip, a 500 sensor linear array from Fairchild. In 1979, an RCA 320x512 Liquid Nitrogen cooled CCD system saw first light on a 1-meter telescope at Kitt Peak National Observatory. Early observations with this CCD quickly showed its superiority over photographic plates. In 1982, the first solid state camera was introduced for video-laparoscopy. CMOS Image Sensors Image sensors are manufactured in wafer foundries or fabs. Here the tiny circuits and devices are etched onto silicon chips. The biggest problem with CCDs is that there isn't enough economy of scale. They are created in foundries using specialized and expensive processes that can only be used to make CCDs. Meanwhile, more and larger foundries across the street are using a different process called Complementary Metal Oxide Semiconductor (CMOS) to make millions of chips for computer processors and memory. This is by far the most common and highest yielding process in the world. The latest CMOS processors, such as the Pentium III, contain almost 10 million active elements. Using this same process and the same equipment to manufacturer CMOS image sensors cuts costs dramatically because the fixed costs of the plant are spread over a much larger number of devices. (CMOS refers to how a sensor is manufactured, and not to a specific sensor technology.) As a result of this economy of scale, the cost of fabricating a CMOS wafer is lower than the cost of fabricating a similar wafer using the more specialized CCD process.   VISION's 800 x 1000 color sensor provides high resolution at lower cost than comparable CCDs. Image courtesy of VISION. Passive- and Active-pixel sensors There are two basic kinds of CMOS image sensors—passive and active. Passive-pixel sensors (PPS) were the first image-sensor devices used in the 1960s. In passive-pixel CMOS sensors, a photosite converts photons into an electrical charge. This charge is then carried off the sensor and amplified. These sensors are small—just large enough for the photosites and their connections. The problem with these sensors is noise that appears as a background pattern in the image. To cancel out this noise, sensors often use additional processing steps. Active-pixel sensors (APSs) reduce the noise associated with passive-pixel sensors. Circuitry at each pixel determines what its noise level is and cancels it out. It is this active circuitry that gives the active-pixel device its name. The performance of this technology is comparable to many charge-coupled devices (CCDs) and also allows for a larger image array and higher resolution. Inexpensive CMOS chips are being used in low-end digital cameras. There is a consensus that while these devices may dominate the low-end of the camera market, more expensive active-pixel sensors will become dominant in niches.   Toshiba Corporation fabricates a 1,300,000 pixel complementary metal oxide semiconductor (CMOS) image sensor. Courtesy of Toshiba. CMOS image sensor facts Here are some things you might like to know about CMOS image sensors: CMOS image sensors can incorporate other circuits on the same chip, eliminating the many separate chips required for a CCD. This also allows additional on-chip features to be added at little extra cost. These features include anti-jitter (image stabilization) and image compression. Not only does this make the camera smaller, lighter, and cheaper; it also requires less power so batteries last longer.   It is technically feasible but not economic to use the CCD manufacturing process to integrate other camera functions, such as the clock drivers, timing logic, and signal processing on the same chip as the photosites. These are normally put on separate chips so CCD cameras contain several chips, often as many as 8, and not fewer than 3. CMOS image sensors can switch modes on the fly between still photography and video. However, video generates huge files so initially these cameras will have to be tethered to the mothership (the PC) when used in this mode for all but a few seconds of video. However, this mode works well for video conferencing although the cameras can't capture the 20 frames a second needed for full-motion video. While CMOS sensors excel in the capture of outdoor pictures on sunny days, they suffer in low light conditions. Their sensitivity to light is decreased because part of each photosite is covered with circuitry that filters out noise and performs other functions. The percentage of a pixel devoted to collecting light is called the pixel’s fill factor. CCDs have a 100% fill factor but CMOS cameras have much less. The lower the fill factor, the less sensitive the sensor is and the longer exposure times must be. Too low a fill factor makes indoor photography without a flash virtually impossible. To compensate for lower fill-factors, micro-lenses can be added to each pixel to gather light from the insensitive portions of the pixel and "focus" it down to the photosite. In addition, the circuitry can be reduced so it doesn't cover as large an area.   Fill factor refers to the percentage of a photosite that is sensitive to light. If circuits cover 25% of each photosite, the sensor is said to have a fill factor of 75%. The higher the fill factor, the more sensitive the sensor. Courtesy of Photobit. CMOS sensors have a higher noise level than CCDs so the processing time between pictures is higher as these sensors use digital signal processing (DSP) to reduce or eliminate the noise. The DSP is one early camera (the Svmini), executes 600,000,000 instructions per picture. IMAGE SIZES The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

In addition, slant polarization can minimize some of the effects of signal variability, reduce interference between antennas and increase the signal-to-noise ratio (SNR). These benefits apply to any operating scenario and especially to urban and other environments where signals are scattered, reducing their strength in a given location.

CMOSvs CCD

The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

Horizontal and vertical dual polarization was used for many years in wireless systems but has mostly been replaced by slant polarization (see Figure 4) in which two linearly polarized antennas radiate at 45-degree angles (+45 degrees and −45 degrees) from horizontal and vertical — that is, midway between the two fundamental polarization angles. Polarization slants don’t have to be 45 degrees, and in some applications including satellite communications systems they’re not, for reasons specific to their operating environments. Of course, the wireless industry could have chosen a variant other than 45 degrees, but having done so, manufacturers increasingly supported it, ensuring its longevity.

Hurdling propagation problems has become more and more important as wireless services employ new modulation techniques, operate at higher frequencies and deploy large numbers of small cells to provide extremely high data rates and low latency. Polarization diversity employing slant polarization along with the innovative use of MIMO-enabled radios are playing a central role in making these possible — and further advances are sure to come.

The model KP-900-DPOMA-45 (see Figure 5) is an example of an omnidirectional ±45-degree slant-polarized antenna for operation between 824 MHz and 928 MHz. It provides 360-degree coverage with minimal azimuth ripple and 10 dBi signal gain. The antenna supports any 900-MHz radio, including the popular Cambium® model PMP450i™. KP Performance Antennas also makes omnidirectional antennas for other bands, including the four-port model KP-25DOMNI-HV that covers the 2300 MHz to 2700 MHz and the band from 5150 MHz to 5850 MHz with a gain of 12 dBi and supports 2×2 MIMO on both bands.

Dual polarization offers other benefits not related to signal propagation but nevertheless potentially beneficial when attempting to receive local approval for antenna installations. It results from having the two antennas together in a single housing, eliminating more than one enclosure. In addition to reduced visual effect, this approach also has little effect on wind loading and adds minimal additional weight.

Fill factor refers to the percentage of a photosite that is sensitive to light. If circuits cover 25% of each photosite, the sensor is said to have a fill factor of 75%. The higher the fill factor, the more sensitive the sensor. Courtesy of Photobit. CMOS sensors have a higher noise level than CCDs so the processing time between pictures is higher as these sensors use digital signal processing (DSP) to reduce or eliminate the noise. The DSP is one early camera (the Svmini), executes 600,000,000 instructions per picture. IMAGE SIZES The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

The third common type of polarization is the generalization of circular polarization, known as elliptical polarization. It occurs when the electric field’s two linear perpendicular components are 90 degrees out of phase and have unequal magnitude. Like circular polarization, an elliptically polarized antenna can be either right- or left-hand polarized. Circular and elliptical polarizations are shown in Figure 2.

Image sensors are manufactured in wafer foundries or fabs. Here the tiny circuits and devices are etched onto silicon chips. The biggest problem with CCDs is that there isn't enough economy of scale. They are created in foundries using specialized and expensive processes that can only be used to make CCDs. Meanwhile, more and larger foundries across the street are using a different process called Complementary Metal Oxide Semiconductor (CMOS) to make millions of chips for computer processors and memory. This is by far the most common and highest yielding process in the world. The latest CMOS processors, such as the Pentium III, contain almost 10 million active elements. Using this same process and the same equipment to manufacturer CMOS image sensors cuts costs dramatically because the fixed costs of the plant are spread over a much larger number of devices. (CMOS refers to how a sensor is manufactured, and not to a specific sensor technology.) As a result of this economy of scale, the cost of fabricating a CMOS wafer is lower than the cost of fabricating a similar wafer using the more specialized CCD process.

Circular polarization is mathematically defined as a linear combination of equal magnitude horizontally and vertically polarized waves that are 90 degrees out of phase. This equates to a wave rotating in time at a steady rate that is either left-hand or right-hand polarized (i.e., spinning in opposite directions) and includes the horizontal and vertical planes and all planes in between. Compared with two linearly polarized antennas of the same orientation and forward gain, having one circularly polarized antenna and one linearly polarized antenna will reduce the link’s range because the circularly polarized antenna splits its power equally across two planes, reducing the system gain by 3 dB. Although this scenario does reduce link budget, circularly polarized antennas are beneficial when the opposite antenna’s linear polarization is not known, or fixed.

cmossensor vs full-frame

Ideally, the transmitting and receiving antennas should have identical polarization because signal strength decreases in direct proportion to how far they stray from that relationship. This is termed polarization mismatch, and the loss in signal strength is calculated in dB as , where, in an ideal scenario, is the angle between the receive and transmit antennas.

Figure 4. At left is horizontal/vertical polarization with respect to the horizon, and at right the depiction is polarized ±45 degrees. The electric and magnetic fields are shown in blue and brown.

All this being said, once an antenna launches a radio wave, the wave’s characteristics continuously change. So, once the wave reaches the receiving antenna, the result is typically the initial polarization modified by fading, reflections, multipath interference, changes in phase and many other factors specific to the operating environment (urban or rural, for example) that affect the received signal strength. These factors can significantly degrade the signal in both strength and quality, and this is where the challenges begin for any type of system.

MIMO communications requires polarization diversity (the use of antennas with different polarizations), one of which is ±45-degree slant polarization. One approach, employed by Mimosa®, combines spatial multiplexing and polarization diversity to allow two data streams to maintain their separation in a way that allows them to arrive with high isolation between them.

Antennas can mitigate some of these problems using various techniques, the most common being polarization diversity. It is used in all types of wireless applications including cellular and the fixed wireless access (FWA) systems used in rural areas to deliver residential broadband service. Polarization diversity is basically the use of antenna systems that radiate signals in more than one polarization, such as horizontal and vertical.

CMOSsensor

The CCD shifts one whole row at a time into the readout register. The readout register then shifts one pixel at a time to the output amplifier. CCD technology is now about 25 years old. Using a specialised VLSI process, a very closely packed mesh of polysilicon electrodes is formed on the surface of the chip. These are so small and close that the individual packets of electrons can be kept intact whilst they are physically moved from the position where light was detected, across the surface of the chip, to an output amplifier. To achieve this, the mesh of electrodes is clocked by an off-chip source. It is technically feasible but not economic to use the CCD process to integrate other camera functions, like the clockdrivers, timing logic, signal processing, etc. These are therefore normally implemented in secondary chips. Thus most CCD cameras comprise several chips, often as many as 8, and not fewer than 3.  Apart from the need to integrate the other camera electronics in a separate chip, the achilles heel of all CCD's is the clock requirement. The clock amplitude and shape are critical to successful operation. Generating correctly sized and shaped clocks is normally the function of a specialised clock driver chip, and leads to two major disadvantages; multiple non-standard supply voltages and high power consumption. It is not uncommon for CCD's to require 5 or 6 different supplies at critical and obscure values. If the user is offered a simple single voltage supply input, then several regulators will be employed internally to generate these supply requirements.  On the plus side, CCD's have matured to provide excellent image quality with low noise.CCD processes are generally captive to the major manufacturers. History The CCD was actually born for the wrong reason. In the 1960s there were computers but the inexpensive mass-produced memory they needed to operate (and which we take for granted) did not yet exist. Instead, there were lots of strange and unusual ways being explored to store data while it was being manipulated. One form actually used the phosphor coating on the screen of a display monitor and wrote data to the screen with one beam of light and read it back with another. However, at the time the most commonly used technology was bubble memory. At Bell Labs (where bubble memory had been invented), they then came up with the CCD as a way to store data in 1969. Two Bell Labs scientists, Willard Boyle and George Smith, "started batting ideas around," in Smith's words, "and invented charge-coupled devices in an hour. Yes, it was unusual—like a light bulb going on." Since then, that "light bulb" has reached far and wide. Here are some highlights: In 1974, the first imaging CCD was produced by Fairchild Electronics with a format of 100x100 pixels. In 1975,the first CCD TV cameras were ready for use in commercial broadcasts. In 1975, the first CCD flatbed scanner was introduced by Kurzweil Computer Products using the first CCD integrated chip, a 500 sensor linear array from Fairchild. In 1979, an RCA 320x512 Liquid Nitrogen cooled CCD system saw first light on a 1-meter telescope at Kitt Peak National Observatory. Early observations with this CCD quickly showed its superiority over photographic plates. In 1982, the first solid state camera was introduced for video-laparoscopy. CMOS Image Sensors Image sensors are manufactured in wafer foundries or fabs. Here the tiny circuits and devices are etched onto silicon chips. The biggest problem with CCDs is that there isn't enough economy of scale. They are created in foundries using specialized and expensive processes that can only be used to make CCDs. Meanwhile, more and larger foundries across the street are using a different process called Complementary Metal Oxide Semiconductor (CMOS) to make millions of chips for computer processors and memory. This is by far the most common and highest yielding process in the world. The latest CMOS processors, such as the Pentium III, contain almost 10 million active elements. Using this same process and the same equipment to manufacturer CMOS image sensors cuts costs dramatically because the fixed costs of the plant are spread over a much larger number of devices. (CMOS refers to how a sensor is manufactured, and not to a specific sensor technology.) As a result of this economy of scale, the cost of fabricating a CMOS wafer is lower than the cost of fabricating a similar wafer using the more specialized CCD process.   VISION's 800 x 1000 color sensor provides high resolution at lower cost than comparable CCDs. Image courtesy of VISION. Passive- and Active-pixel sensors There are two basic kinds of CMOS image sensors—passive and active. Passive-pixel sensors (PPS) were the first image-sensor devices used in the 1960s. In passive-pixel CMOS sensors, a photosite converts photons into an electrical charge. This charge is then carried off the sensor and amplified. These sensors are small—just large enough for the photosites and their connections. The problem with these sensors is noise that appears as a background pattern in the image. To cancel out this noise, sensors often use additional processing steps. Active-pixel sensors (APSs) reduce the noise associated with passive-pixel sensors. Circuitry at each pixel determines what its noise level is and cancels it out. It is this active circuitry that gives the active-pixel device its name. The performance of this technology is comparable to many charge-coupled devices (CCDs) and also allows for a larger image array and higher resolution. Inexpensive CMOS chips are being used in low-end digital cameras. There is a consensus that while these devices may dominate the low-end of the camera market, more expensive active-pixel sensors will become dominant in niches.   Toshiba Corporation fabricates a 1,300,000 pixel complementary metal oxide semiconductor (CMOS) image sensor. Courtesy of Toshiba. CMOS image sensor facts Here are some things you might like to know about CMOS image sensors: CMOS image sensors can incorporate other circuits on the same chip, eliminating the many separate chips required for a CCD. This also allows additional on-chip features to be added at little extra cost. These features include anti-jitter (image stabilization) and image compression. Not only does this make the camera smaller, lighter, and cheaper; it also requires less power so batteries last longer.   It is technically feasible but not economic to use the CCD manufacturing process to integrate other camera functions, such as the clock drivers, timing logic, and signal processing on the same chip as the photosites. These are normally put on separate chips so CCD cameras contain several chips, often as many as 8, and not fewer than 3. CMOS image sensors can switch modes on the fly between still photography and video. However, video generates huge files so initially these cameras will have to be tethered to the mothership (the PC) when used in this mode for all but a few seconds of video. However, this mode works well for video conferencing although the cameras can't capture the 20 frames a second needed for full-motion video. While CMOS sensors excel in the capture of outdoor pictures on sunny days, they suffer in low light conditions. Their sensitivity to light is decreased because part of each photosite is covered with circuitry that filters out noise and performs other functions. The percentage of a pixel devoted to collecting light is called the pixel’s fill factor. CCDs have a 100% fill factor but CMOS cameras have much less. The lower the fill factor, the less sensitive the sensor is and the longer exposure times must be. Too low a fill factor makes indoor photography without a flash virtually impossible. To compensate for lower fill-factors, micro-lenses can be added to each pixel to gather light from the insensitive portions of the pixel and "focus" it down to the photosite. In addition, the circuitry can be reduced so it doesn't cover as large an area.   Fill factor refers to the percentage of a photosite that is sensitive to light. If circuits cover 25% of each photosite, the sensor is said to have a fill factor of 75%. The higher the fill factor, the more sensitive the sensor. Courtesy of Photobit. CMOS sensors have a higher noise level than CCDs so the processing time between pictures is higher as these sensors use digital signal processing (DSP) to reduce or eliminate the noise. The DSP is one early camera (the Svmini), executes 600,000,000 instructions per picture. IMAGE SIZES The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

Justin G. Pollock, Ph.D., is a senior antenna engineer at KP Performance Antennas and RadioWaves, which are brands of Alive Telecom. He is the technical lead on the product development of industry-leading antenna technologies. He has co-authored refereed journal, conference and white papers for leading publications in the field of RF and microwave engineering, antennas, physics and optics.

Another technique for reducing the losses associated with polarization mismatch is MIMO communications, whose best-known benefit is dramatically increasing link performance and capacity by simultaneously sending and receiving multiple data streams. It also exploits the normally detrimental effects of multipath propagation. Even a minimal 2×2 MIMO approach can effectively double the maximum data rate of a communications channel.

Toshiba Corporation fabricates a 1,300,000 pixel complementary metal oxide semiconductor (CMOS) image sensor. Courtesy of Toshiba. CMOS image sensor facts Here are some things you might like to know about CMOS image sensors: CMOS image sensors can incorporate other circuits on the same chip, eliminating the many separate chips required for a CCD. This also allows additional on-chip features to be added at little extra cost. These features include anti-jitter (image stabilization) and image compression. Not only does this make the camera smaller, lighter, and cheaper; it also requires less power so batteries last longer.   It is technically feasible but not economic to use the CCD manufacturing process to integrate other camera functions, such as the clock drivers, timing logic, and signal processing on the same chip as the photosites. These are normally put on separate chips so CCD cameras contain several chips, often as many as 8, and not fewer than 3. CMOS image sensors can switch modes on the fly between still photography and video. However, video generates huge files so initially these cameras will have to be tethered to the mothership (the PC) when used in this mode for all but a few seconds of video. However, this mode works well for video conferencing although the cameras can't capture the 20 frames a second needed for full-motion video. While CMOS sensors excel in the capture of outdoor pictures on sunny days, they suffer in low light conditions. Their sensitivity to light is decreased because part of each photosite is covered with circuitry that filters out noise and performs other functions. The percentage of a pixel devoted to collecting light is called the pixel’s fill factor. CCDs have a 100% fill factor but CMOS cameras have much less. The lower the fill factor, the less sensitive the sensor is and the longer exposure times must be. Too low a fill factor makes indoor photography without a flash virtually impossible. To compensate for lower fill-factors, micro-lenses can be added to each pixel to gather light from the insensitive portions of the pixel and "focus" it down to the photosite. In addition, the circuitry can be reduced so it doesn't cover as large an area.   Fill factor refers to the percentage of a photosite that is sensitive to light. If circuits cover 25% of each photosite, the sensor is said to have a fill factor of 75%. The higher the fill factor, the more sensitive the sensor. Courtesy of Photobit. CMOS sensors have a higher noise level than CCDs so the processing time between pictures is higher as these sensors use digital signal processing (DSP) to reduce or eliminate the noise. The DSP is one early camera (the Svmini), executes 600,000,000 instructions per picture. IMAGE SIZES The quality of any digital image, whether printed or displayed on a screen, depends in part on the number of pixels it contains. More and smaller pixels add detail and sharpen edges.

In antenna design, the horizontal and vertical polarizations often have unequal patterns and gain due to the physical asymmetries of the antenna’s construction. This can be readily observed in each polarization’s patterns, in which the beam width of the vertical polarization is narrower than the horizontal beam width. As a result, the gain of the vertical signal is weaker near the sector edges, which causes a chain imbalance. In a ±45-degree slant configuration, there are no physical asymmetries in the antenna and each polarization has nearly identical patterns that equalize the signal strength of both polarizations.

Cmos on cameraiphone

Charge-coupled devices (CCDs) capture light on the small photosites on their surface and get their name from the way that charge is read after an exposure. To begin, the charges on the first row are transferred to a read out register. From there, the signals are then fed to an amplifier and then on to an analog-to-digital converter. Once a row has been read, its charges on the read-out register row are deleted. The next row then enters the read-out register, and all of the rows above march down one row. The charges on each row are "coupled" to those on the row above so when one moves down, the next moves down to fill its old space. In this way, each row can be read—one row at a time.

CMOSimage sensor

Optimizing signal propagation over wireless transmission paths has never been easy, hindered as it is by obstructions, fading, multipath propagation and various other impediments between the transmitted signal and its intended recipient. Fortunately, there are ways to mitigate some of these factors, ranging from antenna designs and polarization schemes, as well as multiple-input multiple-output (MIMO) communications technology. To understand how these schemes deliver their benefits, it’s first important to cover the basics.

The non-line-of-sight (NLOS) scenario is far more common and presents challenges for all types of wireless systems, especially those in which one end of the link is mobile. When there is no clear line of sight, degradation will result from reflections, refraction, diffraction, scattering and atmospheric absorption. The multiple signals created by these factors will then arrive at the receiving antenna at different times, from different paths and with different strengths. The result will be a reduced link margin and decreased throughput, and in a worst-case scenario, make communications impossible.

Various studies have determined that this ±45-degree slant configuration can provide benefits that H and V configurations do not. Dual-slant polarization is midway between horizontal and vertical and signals from the two antennas combine into a linearly polarized transmitted wave, therefore reception can be improved over pure H or V. Slant polarization has also proven its ability to provide signal improvement through foliage as well as in NLOS conditions.

Figure 5. The model KP-900-DPOMA-45 omnidirectional, ±45-degree slant-polarized antenna for 824 MHz to 928 MHz operation.

There are three general types of antenna polarization: linear, circular and elliptical. An antenna is linearly polarized when it radiates RF energy on a single plane, either horizontal or vertical in relation to the Earth’s surface (see Figure 1) or some angle between both. Radiation from horizontally polarized antennas parallels the Earth’s surface; vertically polarized antennas radiate energy on a plane perpendicular to it.