History of Image Sensor Technology:
– In 1969, Boyle and Smith invented the charge-coupled device (CCD) based on MOS technology.
– RCA proposed a solid-state image sensor with thin-film transistors in 1969.
– A low-resolution NMOS imager was demonstrated in 1981.
– Hybrid infrared focal plane arrays were developed in the mid-1980s.
– The pinned photodiode (PPD) was invented in 1980 and later incorporated into CCD and CMOS sensors.
– The precursor to APS was the passive-pixel sensor (PPS), proposed in 1968.
– Passive-pixel sensors used simple switches for readout and suffered from noise and scalability issues.
Evolution and Development of Active-Pixel Sensors (APS):
– APS contains MOSFET amplifiers per pixel to convert charge to voltage and reduce noise.
– Active-pixel concept was proposed by Peter Noble in 1968.
– The first MOS APS was fabricated by Olympus in 1985.
– Japanese companies developed CMD and BASIS sensors in the late 1980s.
– American companies like Texas Instruments developed practical MOS APS in the early 1990s.
– APS pixels solve speed and scalability issues of passive-pixel sensors.
– APS sensors consume less power, have less image lag, and require less specialized manufacturing facilities compared to CCDs.
CMOS Sensors and HV-CMOS Technology:
– CMOS sensors emerged as an alternative to CCD sensors by the mid-2000s.
– CMOS sensors are widely used in digital cameras, cell phone cameras, web cameras, and DSLRs.
– CMOS sensors use MOSFETs as amplifiers and are more common than NMOS APS.
– CMOS sensors use a pinned photodiode structure for improved performance.
– HV-CMOS devices are used in high-voltage applications like CERN Large Hadron Collider.
– HV-CMOS sensors are specialized for detecting high-energy particles.
Comparison of CMOS and CCD Sensors:
– CMOS sensors are typically less expensive to produce than CCD sensors.
– CMOS sensors have better control of blooming and the ability to reverse the addressing of sensor elements.
– CMOS sensors eventually achieved imaging performance on par with CCD sensors.
– CMOS sensors may exhibit distortion caused by a rolling shutter effect.
– CCD sensors have lower temporal noise and fixed-pattern noise compared to CMOS sensors.
Pixel and Array Design in Image Sensors:
– CMOS APS pixel includes a photodetector, floating diffusion, and a 4T cell with transistors.
– Pixels in a row share reset lines for simultaneous resetting.
– Different pixel designs like 3T and 4T offer varying levels of complexity and functionality.
– Lateral APS structures simplify fabrication processes.
– Thin-film transistors (TFTs) can be used in APS architecture for applications like X-ray imaging.
An active-pixel sensor (APS) is an image sensor, which was invented by Peter J.W. Noble in 1968, where each pixel sensor unit cell has a photodetector (typically a pinned photodiode) and one or more active transistors. In a metal–oxide–semiconductor (MOS) active-pixel sensor, MOS field-effect transistors (MOSFETs) are used as amplifiers. There are different types of APS, including the early NMOS APS and the now much more common complementary MOS (CMOS) APS, also known as the CMOS sensor. CMOS sensors are used in digital camera technologies such as cell phone cameras, web cameras, most modern digital pocket cameras, most digital single-lens reflex cameras (DSLRs), mirrorless interchangeable-lens cameras (MILCs),[citation needed] and lensless imaging for cells.
CMOS sensors emerged as an alternative to charge-coupled device (CCD) image sensors and eventually outsold them by the mid-2000s.
The term active pixel sensor is also used to refer to the individual pixel sensor itself, as opposed to the image sensor. In this case, the image sensor is sometimes called an active pixel sensor imager, or active-pixel image sensor.
