|
An image sensor or imaging sensor is a sensor that detects and conveys the information that constitutes an image. It does so by converting the variable attenuation of waves (as they pass through or reflect off objects) into signals, the small bursts of current that convey the information. The waves can be light or other electromagnetic radiation. Image sensors are used in electronic imaging devices of both analog and digital types, which include digital cameras, camera modules, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, digital imaging tends to replace analog imaging. Early analog sensors for visible light were video camera tubes. Currently, used types are semiconductor charge-coupled devices (CCD) or active pixel sensors in complementary metal–oxide–semiconductor (CMOS) or N-type metal-oxide-semiconductor (NMOS, Live MOS) technologies. Analog sensors for invisible radiation tend to involve vacuum tubes of various kinds. Digital sensors include flat panel detectors. ==CCD vs CMOS technology== Today, most digital still cameras use a CMOS sensor because CMOS sensor technology in recent years has leapfrogged CCDs. CCD is still in use for cheap low entry cameras, but weak in burst mode.〔(【引用サイトリンク】title=Casio Exilim EX-H50 First Impressions Review )〕 Both types of sensor accomplish the same task of capturing light and converting it into electrical signals. Each cell of a CCD image sensor is an analog device. When light strikes the chip it is held as a small electrical charge in each photo sensor. The charges are converted to voltage one pixel at a time as they are read from the chip. Additional circuitry in the camera converts the voltage into digital information. A CMOS imaging chip is a type of active pixel sensor made using the CMOS semiconductor process. Extra circuitry next to each photo sensor converts the light energy to a voltage. Additional circuitry on the chip may be included to convert the voltage to digital data. Neither technology has a clear advantage in image quality. On one hand, CCD sensors are more susceptible to vertical smear from bright light sources when the sensor is overloaded; high-end CMOS sensors in turn do not suffer from this problem. On the other hand, cheaper CMOS sensors are susceptible to undesired effects that come as a result of rolling shutter. CMOS sensors can potentially be implemented with fewer components, use less power, and/or provide faster readout than CCD sensors. CCD is a more mature technology and is in most respects the equal of CMOS.〔(dalsa.com - CCD vs CMOS ) from Photonics Spectra 2001〕〔(dpreview.com - Sensors ) By Vincent Bockaert〕 CMOS sensors are less expensive to manufacture than CCD sensors. Another hybrid CCD/CMOS architecture, sold under the name "sCMOS," consists of CMOS readout integrated circuits (ROICs) that are bump bonded to a CCD imaging substrate – a technology that was developed for infrared staring arrays and now adapted to silicon-based detector technology.〔(scmos.com ), home page〕 Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology. This can be achieved by separating individual poly-silicon gates by a very small gap. These hybrid sensors are still in the research phase and can potentially harness the benefits of both CCD and CMOS imagers.〔(ieee.org - CCD in CMOS ) Padmakumar R. Rao et al., "CCD structures implemented in standard 0.18 µm CMOS technology"〕 The newer sensor technology is Back-side illuminated CMOS (BSI-CMOS) which uses less electricity than traditional CMOS with better performance than CCD, so lower-end cameras still use CCD sensors such as those implemented by Fujifilm in its Bridge cameras. CCD sensors are rarely used in new models, except for very high pixel count, big sensor cameras which still use CCDs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「image sensor」の詳細全文を読む スポンサード リンク
|