The noise present in a sensor (detector) independent of the signal strength or ambient temperature. Normally caused by thermal, generation-recombination characteristics or 1/f effects.
A detector is referred to as BLIP (background limited) when its detectivity D* is limited by the noise associated with the photons from the background radiation and not by intrinsic detector noise.
Complementary Metal Oxide Semiconductor (CMOS)
Semiconductor manufacturing technology in which a silicon wafer is etched with small circuits that allow for signal processing. This technology is used in FPA manufacture and is integrated in most of today's IR imaging systems.
Pertaining to extreme cold. A cryogen is a material which will create extremely cold conditions. Cryogenics is the study of extreme cold. In infrared terminology, cryogenics usually refers to the means used to reduce the detector temperature to a useful value. Temperatures less than 200 K could be considered cryogenic.
The current flowing through a photodiode when a specific reverse bias voltage is applied, with no incident radiant power. Also referred to as Reverse Current.
A parameter used to compare the performances of various detector types. D* is the signal-to-noise ratio at a particular electrical frequency, and in a 1 Hz bandwidth when 1 Watt of radiant power is incident on a 1 cm² active area detector. The higher D*, the better the detector. D* is normally expressed either as a black-body D* or as a peak-wavelength D* within the practical operating frequency of the detector. The units of D* are centimeter-square root hertz per watt.
Field of View (FOV)
The total field measured in an angle within which objects can be imaged or measured and displayed by an infrared system.
Term to measure the FPA performance, which determines how much of the total FPA is sensitive to IR energy. Because the FPA is made of numerous individual detector cells, the total sensitivity is measured by the pathways used to separate the cells and transmit signals. The higher the fill factor, the higher the ratio of sensitivity.
Focal Plane Array (FPA)
A matrix of detector cells attached to a semiconductor chip. The detector cells are responsive in IR wavelengths, in which they absorb IR radiation, convert it into electrons, and output a voltage signal in response to form an image. Technically, FPAs operate much like a charge-coupled device (CCD), which is used in the visible light portion of the spectrum and is found in video cameras. IR imaging FPA detector cells are composed of materials sensitive to IR radiation.
Full Well Capacity
Is the maximum number of carriers that can be accumulated in one detector pixel during one read-out cycle of the detector.
FPAs in a hybrid configuration have an IR-sensitive detector-cell material on one layer, and the signal transmitting circuitry on another layer. Each layer is bonded by a process known as Indium Bump Bonding. The hybrid configuration increases the fill factor and overall sensitivity of the FPA.
A measure of FPA detector performance over the range of temperatures to be observed. The ability of a detector to measure small temperature differences is often referred to as its linearity. Typical testing includes response of the detector from 40 to 50 degrees Celsius (°C) and 490 to 500°C.
FPAs of monolithic configuration have the IR-sensitive material (such as PtSi) and the signal transmission paths (which separate the material's detector cells) on the same surface layer. This technology has its benefits and drawbacks: Although it may be easier to manufacture, a lower fill factor results.
Noise Equivalent Temperature Difference (NETD)
The noise rating of an IR FPA detector specifies the amount of radiation required to produce an output signal equal to the detectors own noise (due to inner component heat). Thus, it specifies the minimum detectable temperature difference. In general, detector cooling is required to limit the detector's own noise and to improve the NETD.
Non Uniformity of Response
The non-uniformity of the electrical characteristics of in-pixel read-out circuitry, as well as of readout components like column amplifiers, endow the final IR image with a static, fixed offset pattern. This pattern has to be removed from each image to yield a useable result. This subtraction of a reference background image can be done off-line, either in the digital or in the analogue domain, both methods requiring an image-sized memory. Alternatively, there are readout techniques for integrating imagers that implicitly remove some non-uniformities. Two of them are double sampling and correlated double sampling (CDS).
Quantum Efficiency (QEA)
Measurement of FPA sensitivity. Quantum efficiency refers to the relative efficiency in which IR energy is collected and converted to an electrical signal. Quantum efficiency is the photon-to-electron conversion efficiency of a photoelectric detector.
Indicates the spectrally active range of an IR detector (given in Hz).