the one and lonely
Image Sensor Lexicon

a collection of terms and abbreviations related to image sensing

1.75T and 1.5T pixels
Are "shared" pinned photodiode pixels (see 4T) organized in groups of typically 2 or 4, whereby the floating diffusion is common. E.g. a group of 4 pixels, having 4 transfer gates, and 1 reset, 1 source follower and 1 column switch, have 7/4= 1.75 transistors per pixel.
1/f noise
Temporal noise with dominantly low frequency content. In this context its physical origin is typically in MOS or MOSFET interface states, known as the "McWhorter model". Synonym of flicker noise.
1T pixel
Consisting of one photodiode and one access MOSFET, the simplest passive pixel.
2T pixel
Two 2T pixels have had some limited success in the past
- Hitachi's 2T pixel is a variant of the passive 1T pixel, with two switches in series, which allows a faster readout and a better FPN cancellation
- Toshiba's 2T pixel is a variant of the 3T active pixel, not needing a select switch. Row selection is done by the supply line to the source follower transistor.
3D imaging
3D imaging is synonym of distance ranging. Severla methosd apply: TOF, stereovision, patterned light imaging etc.
3D integration
Reaching outside the 2D plane as in classic ICs. Routes use waferbonding, TSV, etc.
3T pixel
Most classic and most straightforward active pixel, having three (3) transistors (T) and one photoreceptor. One MOSFET resets the photoreceptor; the second is a source follower sensing and buffering the photoreceptor node voltage; the third is the row selection switch.
4T pixel
There exist several types of pixels with 4 transistors.
The best known 4T pixel is also known as the pinned diode pixel. Take a 3T pixel, and extend the photodiode/floating diffusion node with a transfer gate and a pinned photodiode. Invented by Paul Lee (Kodak) in 1995.
5T amplifier
The ubiquitous CMOS differential pair amplifier having 5 transistors. Called "OTA" by some.
5T pixel
There exists many types of pixels with 5 transistors. Yet in most cases the 5T pixel is the 4T pinned photodiode pixel, extended with a 2nd "flush" (transfer-) gate that serves as electronic shutter and adjustable anti-blooming.
6T pixel
Many pixel topologies with 6 transistors can be devised. Yet this denomination is typically given to a charge domain global shutter (GS) pixels, containing 3 transfer gates (a global TG1 and a rolling TG2, with a memory node in between, and a "flush gate"), and 3 "normal" nMOSFETs for reset, selection and source follower.
absorption depth (~length)
Light, as all electro-magnetic radiation, is absorbed (a necessary condition for being detected!) in Silicon over a characteristic 'absorption' depth. Blue light is absorbed in about 0.5 to 1 µm; green light in a few µm; red light in a layer over 5 to 10 µm thick. Infrared light is absorbed in deeper layers. Ultraviolet light is typically absorbed (thus not detected!) in the covering dielectric (typically SiO2 and SiN) layers.
active pixel
Pixel, containing an active (= power dissipating) element. In most cases the active element is a MOSFET in an amplifying or buffering configuration. The presence of that one MOSFET acting as a switch does not make a pixel 'active'.
active reset
Methods to reset a pixel that result in kTC noise reduction, based on sensing and feeding back to the sense node the pixel?s output voltage during the reset operation.
Analog to Digital Converter: an electronic circuit that converts an analog voltage, as comes out of an imager core, into a digital signal.
alchemy or black magic
The part of our science that nobody really understands, but that seems to work well until someone changes a tiny detail in some arcane procedure.
Anna Karenina-effect (the~)
The observation that one cannot make one real general purpose image sensor (or anything else) that is "good" for all specifications. One-size-fits-all does not work as so easily a spec will fail.
In the novel by Tolstoy, the opening sentence claims that there is only one type of happy (ideal) family, and innumerable ways to be an unhappy family.
The p-terminal of a (photo-) diode.
Properties of image sensors that are inspired by, or similar to, properties of the human (- eye). Examples: logarithmic response, RGB sensitivity, and log-polar geometry.
A feature in CCD and CMOS pixels that counteracts "blooming".
Avalanche Photo Diode.
Photo diode constructed such that it can be operated in "Geiger mode", i.e. it can be biased beyond its breakdown voltage, and breakdown will only happen triggered by the absorption of a photon. This breakdown can be used in photon counting. See also SPAD.
APS (1)
Active Pixel Sensor: Image sensor using active pixels. See also MAPS
APS (2)
Advanced Photo System: small format film, 30.2 x 16.7 mm.
Anti-Reflective Coating: Dielectric layers on top of the receptor with specific thickness and refractive index, so that only a minimal fraction of the light impinging on the receptor is reflected.
area sensor
Imager with a two dimensional array, or matrix, of pixels.
auto-saturation time
The average time for a pixel to saturate due to dark current alone, i.e. non-illuminated. The absolute upper limit for useful integration time.
Bayer pattern
A popular type of Red-Green-Blue CFA, invented by Brice E. Bayer (Kodak).
Or "charge binning"
A mode of operation that is available only in certain types of CCD (FTCCD) and some shared pixels. The charge of multiple pixels is accumulated and read in a single operation. This type of binning has no noise penalty. Binning is sometimes emulated in passive pixels, active pixels (voltage binning) or in the digital domain. But here the noise advantage is less prominent.
black shoe under the table -test (the~)
Quick image sensor test done by hasty procurement officers at camera system companies to evaluate the low-light capabilities of a camera or sensor. In an office, with a comfortable 200 to 1000 lux illumination, the darkest spot is under the table, the darkest object readily available there is a black shoe. Does it image well?
blinking pixelpixel that has a dark current that varies significantly over time, typically as RTS.
Background Limited Integrated Performance: camera operation in a condition where the noise is dominated by the inherent shot noise in the background illumination level. Term used in IR imaging.
Radiation detector sensor/pixel based on the change of temperature due to radiation absorption. The change in temperature is sensed and readout through a strongly temperature dependent resistance.
Backside illumination and backside thinning.
An imager can be illuminated from the backside, if the silicon can be uniformly thinned to a few micrometers. If successful, there is no obstruction of the light by metallization and dielectric layers, and the fill factor and UV sensitivity can be very high.
Bulk or Substrate (see SUB). With MOSFETs, bulk or substrate is labeled B.
bulk effect
Normally the source-drain current through a MOSFET is controlled by the gate potential. Nevertheless, the bulk potential has a generally unwanted parasitic effect too.
buried channel
Similar to a MOSFET inversion layer, but by the proper game of implantations the charge is separated from the interface.
The better "buried channel" CCDs store and transfer their charge in a buried channel under the electrodes.
buried diode
Photo diode which by an additional junction/implant is separated from the Si-SiO2 interface. This implant ?pins? the interface potential to a fixed value, likely the substrate potential. Its main effect is a reduced dark current, as it electrically separates the interface dark current generation centers from the collecting junction. See also pinned diode.
Caeleste CVBA, "beyond state of the art" image sensor developer and supplier, specialized in high-end space, medical and industrial image sensors. For the origin of the name, see
a historic serial communication protocol and cable format designed for computer vision applications. Successors to CameraLink are GigE, 10GigE, HDBaseT, emcore, CoaxPress, LAG, USB3
The n-terminal of a (photo-) diode
Charge Coupled Device: Originally the name of a structure invented in 1970 of adjacent MOS gates ("electrodes") that allows both confinement (storage) and transport of free charge. Later the name of the modified MOS technology in which the device is made. Even later the name of image sensors based on the CCD principle. And finally, sometimes, the generic name of a solid state image sensor.
Correlated Double Sampling:
A method to read the differential magnitude of a charge packet as the difference between a "signal" and a "reset" sample, thereby canceling a source of FPN, as well as the kTC noise that is caused by the reset of the capacitance holding the charge packet.
Estimating the position of the center of a light spot with a finer resulting than the pixels pitch. A form of super-resolution.
Charge feedback amplifier, a synonym of CTIA
Color Filter Array: the mosaic of color filters overlaid on the pixel array.
CFD [fF]
Floating diffusion capacitance.
Contrast Transfer Function: MTF multiplied by S/N. An attempt to define an image sensor quality factor that favors both sharpness and contrast.
charge skimming
Also named "direct injection", is a technique to sense charge with a high charge-to-voltage conversion ratio. The photodiode (or photo resistor) is at the source of a DC-biased MOSFET. The charge is integrated at the drains side of the MOSFET. Is used in the classic 4T pixel.
cheerleader effect
A classic misconception that nature systematically compensates bonuses by flaws. e.g. that beautiful girls must be dumb; that smart people must be nerds or socially inapt; that CMOS image sensors must be low end.
See "die"
Charge Injection Device: CCD-based technique and image sensor using this technique. Detection based on local charge transfers only and non-destructive read out.
CIE diagram
Two-dimensional [x,y] representation of [X,Y,Z] color space. It can represent all physical colors (and even more!). I.e. any combination of monochromatic wavelengths, which is much more than what can be generated with a set of three primaries (typically R,G,B). All colors that can be generated by the linear combination of such primaries form a color triangle. CIE = Commission Internationale de l' Eclairage
CMOS Image Sensor
Charge Modulation Device: Image sensor technology based on the detection and charge sensing in isolated bulk (B) node of a (buried channel) MOSFET.
Complementary MOS: The mainstream mass manufacturing Silicon technology. Characterized by the fact that both nMOSFETs and pMOSFETs ("complementary" pairs) can be manufactured on the same wafers.
Correlated Multiple Sampling:
The same as CDS, yet each of the reset and signal samples are themselves the average of multiple sampled values. It improves on CDS by further reducing noise contributions.
Chip On Board: Mounting the image sensor chip directly on the PCB, without package. Cheap but a bit fragile, unless well protected.
Answer to the question: shouldn't we put a larger part of the system (digital or analog) on the same chip as the analog imager core?
human subjective experience of pure or a mixture of monochromatic wavelengths.
color reconstruction
(or "demosaicing"). The raw image from an imager with CFA has only one color component per pixel. Trivial or cleverer reconstruction algorithms must restore the missing color components for every pixel.
column amplifier
Charge amplifier or voltage amplifier that is located at the edge of columns of pixels. Serves to buffer or sense the signal of one, selected, pixel in the column. Typically, the signals of the column amplifiers are multiplexed to one imager core output.
"Conservation of Misery". When you improve on one parameter (say, noise), you will inevitably sacrifice another parameter (say power, area, speed, design time, profit, salary?). It does not work the other way around: when you deliberately worsen say, noise or power, speed or your salary will not improve. Has some affinity with the Laws of Thermodynamics (conservation of entropy), the Law of Murphy and the Anna Karenina effect (see above).
cosmetic defect
As a spot or a mark in the face. Small defects, localized non-uniformities, unwanted patterns, blemishes, dust particles, etc. that degrade the image quality.
cosmic radiation
A mix of high energy radiation coming from outer space, and in majority emanating from the sun. The charged particles (H+, e-, ions) are stopped by the Van Allen belts and the upper atmosphere; photons and neutral particles (neutrons, muons?) may penetrate the atmosphere.
Chief ray angle: angle under which the "chief" (central, main, average) rays hit the imager surface.
Cathode Ray Tube: the ancient display device, used in TV and computer monitors. Now largely replaced by LCD or OLED displays.
Charge Trans-Impedance amplifier. Amplifier, not in the sense of voltage multiplier, but in the sense of translating the signal to a different domain, in casu, charge to voltage domain. A "charge-to-voltage" amplifier thus. The classic full-bred CTIA is an inverting amplifier with a capacitor in the feedback (also called CFA charge feedback amplifier); but simply storing a charge on a (parasitic) capacitance, and reading the voltage with a source follower, as in the 3T pixel, is also a CTIA in principle.
cushion effect, cushioning
Light flux projected through a lens is more attenuated at the sides and corners of the image. The response over the image area has the shape of a pillow / cushion. The effect is caused by the reduced angle of incidence away from the image center, and by the non-Lambertian absorption of the imager. Is modeled by cos2 to cos4 laws.
Extreme cushioning is called "vignetting". Sometimes also pincushion- or barrel distortion is called cushioning.
Charge to voltage conversion ratio [µV/electron]
Conversion gain [µV/electron]
Specific detectivity. A figure of merit for the capability of a receptor or receptor technology, which is invariant for area and integration time. Used in IR vision.
Digital to Analog Converter: as ADC, but read the explanation back to front.
Shorthand for "demonstration effect" (or ?demolition-effect??). An empirical law stating that nice setups fail at or just before an important person comes to see it. See also CoM.
See color reconstruction
"Detecting" apparatus. Most people don't tell the difference with "sensor". Sounds more "active" than "sensor" - or does it sound more expensive? The nuclear physics community considers a detector as the bigger apparatus containing many smaller "sensors". In hybrid FPAs the detector is the non-Silicon part of the (image-) sensor.
Dividing a wafer into dice by scribing/breaking or sawing
die (plural: dice): rectangular piece of semiconductor material, thus more or less a synonym for ?chip?. A die or chip may contain one or more (!) ICs.
dielectric layers
Insulating, transparent (?) layers on top of the IC. Typically SiO2, SiN. Recently "low-k" dielectrics (polymers, black diamond, porous materials) are being introduced to lower the inter-metal capacitance for high speed and RF applications.
Electronic device with two terminals that conducts the current in only one direction. Originally a two-terminal vacuum tube, discovered by Edison in 1880. Nowadays it consists of a p-n junction, the juxtaposition of an n-type semiconductor and a p-type semiconductor, typically on the same substrate.
Disneyland set (the~)
Yes! There exists a publicly accessible calibrated scene for camera evaluation that does not look like a nearly bankrupt furry animal and grocery shop: Disneyland under a blue sky. Make a set of pictures of your kid in every attraction while your boss signs the expense note.
double slope integration
Method to extend the dynamic range of a normally linear-transfer imager, by combining the images taken with a long and a short integration time into one image. The resulting electro-optical transfer curve is bi-linear.
Detective quantum efficiency [%]. Quality factor used of X-ray detectors, combining the absorption, S/N ratio and MTF.
Dynamic range.
ratio of highest non-saturating optical flux on the smallest detectable flux for a sensor. Is equal to the SNRmax if and when the sensor features a linear transfer curve, see here.
Dark signal. The signal due to dark current Idark, expressed in [V/s].
Double Sampling or Uncorrelated Double Sampling: A method to read the magnitude of a charge packet, canceling a main source of FPN, but not the kTC noise.
Differential or incremental or "AC" S/N ratio. Similar to S/N *but* the signal is considered explicitly as the small signal fit to the non-linear S/P (signal/power, or response) curve. dSNR is a lower number than SNR when considering the typical non-linearities seen in real systems.
Dark Signal Non Uniformity, expressed in [V/s]RMS or VRMS. The spatial noise due to the pixel-to-pixel non-uniformity of the dark current.
Digital Signal Processor: software-programmed or hardwired logic device, specialized in performing many calculations at high speed on a signal. The raw image coming from an imager can be/needs to be post-processed in the digital domain.
dummy pixels
A pixel array features some rows/columns of real but unused pixels at its perimeter, thus ensuring that the "useful" pixels are not affected by peripheral circuitry. Also called ?guard pixels?.
Elementary particle with negative unit charge.
Electroniad or Electroniade
Electronics quiz and championship, organized by Caeleste on 14 October 2016 in Technopolis, Mechelen. See . The second Electroniade was organized by EASICS in Leuven on 15 September 2017.
electronic shutter
A method to operate an electronic image sensor in a way that the effective integration or exposure time (shutter time) is variable. The result is the same as that of the mechanical shutter found on the classical photo camera.
Electro-Magnetic radiation: Visible light is just one small part of the huge EM spectrum.
Electro-Magnetic Compliance: the property to emit no (or little) radio wave EM radiation, or to be insensitive for spurious EM radiation or EMI.
Electron-multiplying CCD
Electro-Magnetic Interference; various types of system level noise entering the IC via the air, IO wires and supply/ground wires.
Epitaxial layer or wafer. Most CMOS image sensors need processing on highly doped wafers with on top a few microns thick "epitaxially grown? layer of lowly doped silicon.
Interference pattern at the NIR side of the Silicon spectrum due to multiple reflections between the two parallel interfaces in (e.g.) a BSI wafer.
excess noise
Noise exceeding the theoretical PSN, as caused by electron and hole multiplication in Si, as in APD, SPAD or EMCCD.
I many cases still the standard by definition in electronic vision. Giant imperfections conveniently hidden by the huge image correction engine behind it.
floating diffusion.
Circuit technique for the conversion of (photo) charge to a voltage, on a (not tied to a DC voltage, thus "floating") junction (junctions were historically created by impurity diffusion). Used in most CCDs and APSs. Invention attributed to Walter Kosonocky, but disputed to have been conceived already by Noble.
Field Emission Array: Micro-machined silicon device that combines the light detecting mechanism of a Vidicon tube and the circuit possibilities of an integrated circuit.
Front-end electronics.
The driving electronics that reside close to the FPA.
Full Frame CCD: A FT CCD lacking storage area. Needs an external shutter.
fframe [Hz]
Frame rate, the frequency at which frames are acquired
fill factor
FF: ratio [%] of the light sensitive area of a pixel on its total area. Should be quoted in conjunction with spectral response.
Light power per unit area [W/m2]. Light intensity. Irradiance.
(sometimes written as f# or f/#) Ratio between the opening (diameter) of the lens and its focal length. A high f-number means a large attenuation of the light power. A low f number is beneficial for low light imaging, but low f-numbers have also low depth of focus and are vulnerable to lens imperfections:
Focal Plane Array.
The image sensor as placed in the focal plane of a telescope.
Fixed Pattern Noise, or spatial noise. Is the unwanted static (DC) variation of the response of all pixels in the image. Expressed as an offset in volts or in ADC bits.
Fixed pattern non-uniformity, identical to FPN, but this term makes it more explicit not to be ?N? or temporal noise, conformant to PRNU and DSNU. Caeleste coined term.
The electronic form of one image.
Frame Transfer CCD.
Control terminal of a MOSFET. In a CCD the gates are called "electrodes".
Response correction in cameras originally introduced to counteract the non-linear response of CRTs. The typical gamma correction takes the signal - or each of the R, G, B components - to the power of 0.45.
gamma rays
see X-rays
Ground. The zero reference voltage in most electronic circuits. In our science it is typically defined as equal to the substrate voltage, sometimes simplistically called substrate potential.
Graceful degradation
When going outside its specified operation domain (temperature, supplies, signal quality?) a device should not suddenly fail, rather gradually ("gracefully") degrade, thereby remaining as operational as possible.
gray [Gy]
SI unit of radiation dose, used in X-ray and particle imaging. A dose of 1Gy corresponds to a radiation energy of 1J deposited in 1kg of material (body tissue). For a relation between dose in Gy see here.
grey world
A simple and generic approach to white balancing: the average response of R, G and B is equal, as if the scene (world) is grey.
Global shutter. See synchronous shutter
Hue. A quantity indicating the spectral component of a color. The "H" in LHS. Scalar number indicating the spectral component continuously from read-yellow-green-cyan-blue-magenta-red.
Hole Accumulation Diode. Trademark of Sony. Sony reports a very good CCD or CMOS photodiode, very similar to what is otherwise known as a PPD.
Motion blur due to the shaking of the hand of the photographer.
Feature of many transmission protocols, for establishing the data channel or to acknowledge correct receipt.
High dynamic range
"high resistivity", in this context very lowly doped wafers or epi-layers, allowing deep depletion layers, typical for enhanced QE for NIR, X-ray and particles.
In a semiconductor the local absence of a bound electron, acting to all intents and purposes as a free charged particle with positive unit charge, and thus opposite of a negatively charged free electron. A hole is absolutely not the same as a positron, the anti-electron, which also has a positive unit charge, but which is a real physical (but rare, and thus expensive) particle.
horror vacui
Fear of emptiness (Latin). The natural fear of an image sensor designer for empty silicon, and her/his insuppressible desire to fill this space with circuits, test structures, yield killers, logos, etc.
Imager consisting of a CMOS readout array chip and a separate detector chip.
Intrinsic or i-type.
Undoped Silicon has (in theory) a low concentration of both holes and electrons. To distinguish it from n- or p- type, it is indicated by "i". The "I" in PIN (see there).
Integrated circuit
An electronic circuit manufactured on one piece of semiconductor. There may be one or more ICs on a single die or chip.
dark current
The parasite of photocurrent. In the absence of light, a non-zero current will flow in the photodiode, spoiling the image and adding its own shot noise. Typically expressed in [pa/cm2], in [electrons/second] or in [V/s] (see dark signal).
InterLine (transfer) CCD.
Combination of the words image and sensor.
imager core
The essential part of an image sensor chip. Nothing more than the pixel array and the immediate peripheral circuits required to operate the pixel array.
intelligent image sensor
Smart sensor.
The real question is: what is "intelligent"? The first image sensor that can give an answer to that question is really intelligent.
Radiative power per unit area; flux. Expressed in [W/m2] or [lx] (see luminance)
interface (1)
In this science (CMOS technology) the border between Silicon and whatever is on top. The favorite meeting place for embarrassing things like dark current generation centers and 1/f noise sources.
interface (2)
At system level it usually is the hardware/software entity that links camera or camera chip to a system. Examples: video (PAL, NTSC), FireWire, USB3, CameraLink, CoaxPress...
In the CCIR (PAL) and EIA (NTSC) video formats, the image information was divided in odd and even (sub) frames. Alternating frames contain only the odd or even lines. Imagers for these formats should read their lines in the same sequence. Interlacing is a completely useless feature. It is/was maintained because of the historical way video standards have grown. Present day formats use ?progressive scan? without interlacing.
inversion layer
Under the influence of an electric field an n-type material can contain a majority of holes, and thus "invert" effectively to p-type, or vice versa. The inversion layer under a MOSFET gate is the conducting path of the MOSFET.
Image Processing: Digital domain operations in hardware or software on images or image sequences.
· "early" operators are intended to convert the raw image from the imager to a "nicer" image.
· "later" or "smart" operators do something with the image contents.

Typical "early" image processing operators are: spatial and temporal filtering, non-uniformity calibration, defect corrections, offset and gain correction, gamma correction, color reconstruction, demosaicing, white balance, saturation and hue correction, ?matrixing?.

Amongst "smart" operators are: image compression, code recognition, image interpretation, segmentation, correlation, feature recognition, automatic measurements, demodulation, time gating, distance ranging, ...
?Intellectual property?. In the IC design context often means re-usable standalone major sub circuits, such as ADC, memories etc. that are obtained from 3rd parties, or by extension self-developed.
Infra-Red: EM radiation with wavelengths longer than the visible light. The following names are often used to denominate IR bands:
NIR: near infra-red, 700-1100 nm ("Silicon" NIR), or 700-2000 (spectroscopy NIR) SWIR: short wave infrared: As NIR, but without the Silicon part, say 1200..2500nm. MIR: mid infra-red, 3.5-5 µm, the first atmospheric thermal window TIR: thermal infra-red, 8-14 µm, the second atmospheric thermal window, including the peak emission of blackbodies at ambient temperature. FIR: far infrared, 14-1000 µm, only of scientific interest. Terahertz waves / ~imaging: EM radiation 1-10 THz or 30-300µm Sub-millimeter waves / ~imaging: 300GHz-1THz or 300µm-1mm Millimeter waves: 30GHz-300GHz, or 1-10mm
IR cut-off filter
Silicon photodiodes are sensitive for light with wavelengths between 350 and 1100 nm. The human eye sees light with wavelengths between 350 and 750 nm (the "visible spectrum"). An IR cut-off filter is a piece of special glass, or another material, put in front of the image sensor and absorbing or reflecting the light outside the visible spectrum. Necessary for color sensitive imagers.
Empirical measure of the light sensitivity or speed of photographic film. Transferring this to an electronic image sensor spec is a real shot in the dark. See ISO standard 12232.
Imager system on chip
Integrate-then-read, often a synonym for sequential or triggered synchronous shutter
jello effect
Motion artifact observed in rolling shutter imagers
The place where a two materials join. In semiconductor diodes: the border between the p- and the n- material.
knife edge method
A method to obtain the LSF, hence the MTF, by illuminating a pixel over a sharp edge, as that of a knife.
Boltzmann?s constant * absolute temperature * capacitance. The thermodynamic uncertainty on the amount of charge left on a capacitor after disconnecting it from a DC voltage source. kTC noise is sometimes called "reset noise".
The human vision spectrally weighted "light intensity" or "black&white" component of a color image, or of a color video signal. The "L" in LHS, the "Y" in YUV. Carries sharpness, contrast, dynamic, dark/light/grayscale. Luminance is proportional to light power. The CIE notion "lightness" (L*) is a non-linear perceptual derivate of luminance. The notion "Luma" (Y') is a video-technique non-linear look-alike of luminance.
Liquid Crystal Display: One type of flat panel display, based on the light polarizing capabilities of so called liquid crystals in an electric field.
luminance - hue - saturation: an alternate way to represent colors in a 3 dimensional space. Is more suitable for certain image processing algorithms than the RGB space.
Light-radar. Distance ranging using light. A synonym of TOF.
linear response
a light power (P) to voltage (V) conversion that can be approximated by a linear relation as: V = something * P.
linear sensor
Image sensor with a one-dimensional array of pixels, i.e. one or a few rows of pixels. Don't confuse it with a linear response image sensor.
logarithmic response
A light power P to signal voltage V conversion that can be approximated by a logarithmic relation as: V = something * log(P).
log-polar geometry
Arrangement of pixels, organized in concentric circles, with a constant number of pixels per circle. The pixel size is smallest in the center (pole) and grows exponentially (1/log) towards the edges. This mimics the human retina.
Line Spread Function: the Point Spread Function (PSF, see there) projected on one dimension. MTF is the Fourier transform of the LFS or PSF.
lux [lx]
Human eye equivalent (i.e. subjective) of the objective light flux measured in W/m2. As the spectral sensitivities of the eye and Silicon are not matched, there is no general conversion factor between lx and W/m2. As a rule of thumb, consider 1W/m2 = 100lx (visible white light) to 250lx (visible + NIR).
Monolithic active pixel sensor
Early image processing operator that can be described as a 3x3 matrix operation on the R, G and B color channels. It implies white balancing and hue/saturation correction.
micro lenses
Technique to increase the fill factor of pixels by giving each pixel a tiny individual lens that converges all light on the even-tinier photodiode below it.
Metal Oxide Semiconductor: In medieval times MOSFETs were made as a stack of Aluminum (metal) on SiO2 (oxide) on Silicon (semiconductor). Today the gate metal is in most cases replaced with Polysilicon or Silicide Polysilicon, but the name persisted. (yet in deep-deep-submicron processes, metal gates or fully silicided gates reappear again).
MOS Field Effect Transistor: transistor type based on the MOS layer structure. The current between source (S) and drain (D) passes through the inversion layer that is controlled by the voltage at the gate (G).
Motion blur
Unsharpness in an image causes by the object, the scene, or the camera moving during the integration time.
Modulation Transfer Function: Ratio between the amplitudes of a sinusoidal pattern in the optical image and the resulting electronic image. A measure for a pixel's / sensor's inherent sharpness of focus.
multiple slope operation
as double slope, with more than 2 slopes.
Vnoise Qnoise
A word with many meanings. In our science it is the unwanted fluctuation, or measurements error, of the signal of one pixel over time. To differentiate from spatial/static noise it is sometimes called "temporal noise" (N, Vnoise [VRMS] or Qnoise [electronsRMS])
Numerical aperture. 2NA = 1/f#
Non-Destructive Readout. Mode of operation of CCDs and CMOS image sensors, where the size of a charge packet is read, without resetting it. This information can thus be read several times (oversampled), so as to improve the S/N of the reading operation.
Called "Fowler sampling" by the US IR community, although the method was in use @ ESA before the 1990 Fowler publication. See e.g. [D. Engemann & al. 'Infrared detector arrays with multiplexing cryogenic read-out electronics for ISO'. 4th International Conference on Infrared Physics, Zurich 11-11-1988. Published in Infrared Physics, vol.29, no.2-4, pp.235-241 (1989).] Hence the method should be called 'Engemann sampling'.
Noise Equivalent Power. In [W] or [WRMS]
Near InfraRed: EM radiation between 750 and 1100 nm, invisible for the eye, but still visible for Silicon. For non-Silicon guys, NIR means 750-2000nm. See also SWIR.
Non-linearity, in image sensors meaning the non-linearity of the PR
Non-linearity non-uniformity (Caeleste coined term). The variability, over the pixels, of the NL.
n-type MOSFET, a MOSFET in which the conduction between n-type source and drain happens by electrons.
Under zero electric field and equilibrium an n-type semiconductor contains a majority of electrons and few holes. n-type Silicon is usually obtained by doping with donor ions.
Nyquist limit
The Nyquist limit (fNyquist) equals to the spatial frequency 1/(2 x pixel pitch) of a pixel array. Image information beyond this limit is "aliased" to lower spatial frequencies. In practice this aliasing appears as Moiré effects and color artifacts.
optical cross talk
Light impinging on a pixel can influence the signal of neighboring pixels through various mechanisms: diffraction of light, diffusion of photo charge towards the neighbor, or plain electrostatic cross talk. Together these make up optical crosstalk.
passive pixel
Pixel not containing an active element, so essentially a photodiode with access switches. The most obvious passive pixel is the 1T pixel.
photo diode
All silicon diodes or p-n junctions are sensitive to light. A diode that explicitly is designed for detecting light is a photo diode.
photo gate
Light receptor made as a MOS structure. Can be understood as a p-n photo diode, where one of the parts is the inversion layer under the MOS.
photo receptor
or light receptor. The light sensitive device in a pixel (in this science). Typically a photodiode, a photo transistor or a photo resistor.
photodiode array
Image sensor consisting of an array of passive pixels, where the passive pixels contain only a photodiode and a multiplexing switch.
photoelectric effect
The basic mechanism of light detection in any solid state (and other) imager. A quantum of energy from the impinging EM radiation (a photon) excites a bound electron to an unbound state.
The light quantum. The unit of energy exchanged in a single interaction between EM radiation and a charged particle.
"Mr. Dierickx, I don't believe in photons. I only believe in things that I can see with my own eyes."
photon counting
Detecting individual photons and counting these events.
PIN diode
p-n diode with a relatively important lowly doped (intrinsic) layer "i" sandwiched between the p-type and n-type regions. Due to its deep collecting volume suitable for IR and X-ray detection. Due to its thick depletion layer having a low capacitance.
From picture + element. Originally the atom of a photograph, of an electronic image, of an electronic display. In our profession the atom of an image sensor. Minimally contains a receptor and elementary means to feed the information to the outside world.
p-type MOSFET, a MOSFET in which the conduction in the inversion layer between p-type source and drain happens by holes.
pinned diode
Pinned (photo-)diode: buried (photo-)diode with the additional feature that it can be completely depleted, and thus emulate complete charge transfer as in a CCD.

photo response, response, (photo-) responsivity. What an image sensor or pixel really does: to respond with a 'signal' (typically a signal is a voltage [V] or a voltage slope [V/s]) as a response to light ('photo') (typically expressed in W, W/m2, lx). The usual units of responsivity are thus V/W, (V/s)/(W/m2), (V/s)/lx, and alike.
Click here for a view on the contributors to photo response.
(see also "Trappist") due to the proliferation of non-alcoholic image sensor designers in Caeleste, the alternative reward for finding an error.
preview mode
Mode of operation of a large, slow-scan, imager: It is read at high frame rate but at reduced resolution. "Video mode".
Photo Response Non-Uniformity
non-uniformity in the slope of the photo-electric transfer curve between pixels. Also see spatial noise.
Position Sensitive Device: A solid state optical sensor that outputs analog signals that are measures of the position of a light spot on the sensor.
pseudo-random CFA
mosaic color filter array, where the colors are attributed to pixels in a (pseudo) random way. The purpose is to suppress color-moiré or color-aliasing. There is some anthropomorphic aspect in it too.
Point Spread Function.
The "effective shape" of a photodiode. MTF is the Fourier transform of the LFS or PSF.
Photon shot noise.
The fundamental statistical uncertainty on the amount of photoelectrons that are generated by light falling on a photoreceptor.
Under zero electric field and equilibrium a p-type semiconductor contains a majority of holes and few electrons. p-type Silicon is usually obtained by doping with acceptor ions.
push broom imager
A linear imager scanning a two-dimensional scene. Often used for earth imaging.
quantum efficiency
Ratio [%] between the number of generated electrons and the number of impinging photons. Closely related to spectral response.
QFW, Qsat
?Full well? (or ?saturation?) charge, a term persisting from the CCD era: the maximum charge a pixel can contain and readout. Used as a synonym is saturation charge, the charge at which the pixel saturates.
Noise charge, generally expressed in ?noise electrons? [e-RMS]
random addressing
A mode of operation of an image sensor, where pixels are addressed and read individually and randomly, like a RAM or ROM.
The generic name of an elementary radiation sensitive device. Photodiodes, film grains, eye cones and rods are examples of light receptors.
rel DE pixel R*
Magnitude of the responsivity of a pixel referred to the threshold of nominal light detectivity. Is a measure for the capabilities of a specifications writer. Introduced by Joel "Noise" Neys of FillFactory in 2002.
Reset pixel control. In the imager context, reset means clearing or emptying the charge contents of a pixel to the initial dark value.
Red Green Blue: In most color cameras light is separated in 3 components labeled red, green and blue. This matches the 3-color sensitivity of the human eye and the 3 phosphor emission of color TV displays.
Alternative, complementary, colors are sometimes used: Ye (yellow), Cy (cyan) and Ma (magenta). The choice is not even limited to these 6 colors.
Region of interest. See Windowing.
Read out IC: the (almost always CMOS) readout part of a hybrid image sensor.
Rolling shutter. Also curtain shutter, blade shutter. Moving slit mechanical shutter as used in SLR photo cameras. Ubiquitous type of electronic shutter which does not expose all of the image's pixels in the same period of time. Contrary of synchronous shutter. Btw rolling shutter on its own is a completely useless feature. It exists because it is suitable for the classic 3T and 4T pixels.
Random Telegraph Signal. The noise of a single trap or interface state, seen in
(1) stepwise two-level variation of MOSFET Vth. Is of the same origin as MOSFET 1/f noise, presumably interface charge traps modulate the conductivity of part of the nearby MOSFET channel.
(2) stepwise variations of rate of a generation center. This is seen in pixels with a random on/off keying of the dark current. the origin seems to be a geometrically close pair of a generation center and a coulomb trap. The coulomb trap's state modulates the generation center's rate. Are often seen as the result of displacement damage by proton or other heavy particle radiation. See "blinking pixel"
Read while integrate
Pipelined synchronous shutter
Signal. The output of a pixel or image sensor, usually in volts [V], or in ADC counts
Source. One of the terminals of a MOSFET.
saturation (1)
The light level (the input quantity) or voltage (the output quantity) at which the pixel has received so much light that its differential response drops to zero.
saturation (2)
Property of a color, more or less synonym to spectral purity. unsaturated colors are pale or greyish. Back, white and grey have zero saturation. Maximal saturation occurs for pure spectral colors. The "S" in LHS.
Schottky diode
A heterojunction diode between a semiconductor and a metal (or metal-like substance). Several Si-metal diodes have a lower forward voltage than a Si p-n diode, and a related longer optical cut-off wavelength.
Material in which X- (also γ and UV-) photons convert into a visible light flash, which are subsequently detected in an underlying image sensor.
scribe lane/line
Area between chips/dice on a wafer, intended to be scribed or sawed. These ~100µm waste gaps are often used for in-process or process validation test structures.
Single event
Single event effect
Single event latch-up
Single event upset
The desired property of a good sensor. The semantic difference with detectivity and responsivity is not clear. Often sensitivity is intended to express the ratio between voltage signal (V, V/s) versus light flux (W/m2, lx), resulting in units as [V/lx.s] or [V.m2/W.s].
"sensing" apparatus.
In our world, a circuit that in some way is able to sense the amount of incoming electromagnetic radiation. Most people don't sense a difference with "detector".
Digital circuit that generates the pulse trains that are necessary for the proper operation of an analog imager core.
Source follower.
Near unity gain buffer amplifier very frequently used in CMOS pixels and CCD, whereby the output is the MOSFET source, following the input on the MOSFET gate.
Single Lens Reflex (-camera)
DSLR: Digital SLR
smart pixel
Pixel with built-in intelligence, which can be analog or digital operators, event triggering, event counters, smart reset, systolic arrays, ADC-in-pixels, etc.
smart sensor
Imager combined with logic, on one chip. The chip should interpret, rather than just output, the image contents.
Storage node, or memory node of a charge domain global shutter pixel
snapshot shutter
See synchronous shutter; ITR
Signal to noise ratio: Ratio between the signal (in volts) and the noise level (in voltsRMS). By default, it is understood that S and N are considered in the same operation point, but often, marketing oriented people use S at large signal and N at low signal.
Maximum SNR, whereby the S is taken at or near saturation, and N in the dark.
Single Photon Avalanche Diode. See APD. The same as an APD in ?Geiger? mode.
spatial noise
The generic description of static (non-temporal) non uniformity or variability in the imager. The three most prominent components are FPN, PRNU and DSNU. See under these entries.
Spectral Response. Response of a photoreceptor as function of wavelength. In most cases the ratio between the photocurrent and the light power (or: photo current density and light flux). Expressed in [A/W].
lithographical composition of a large area image sensor by many exposures of smaller entities
storage gate
MOSFET gate or CCD electrode that stores charge in the inversion layer or buried channel underneath.
(1) year ring -like modulation of dopant concentration in grown crystals and thus in wafers. Can sometimes become visible in an image sensor's image, as offset variations (FPN), as PRNU, or as dark current variations.
(2) radial lithographical faults due to photoresist hindered by the wafer topography during spinning.
Substrate. The bulk of the integrated circuit. The "useful" circuits normally lie only on or just below the surface.
Mode of operation of an image sensor. Pixels are read sequentially, but not contiguously. I.e. some pixels are skipped, to obtain an image with lower resolution, and perhaps at a higher frame rate.
Extracting positional information from an image by exploiting knowledge about the object. Examples: centroiding, unmixing
Swank noise
Temporal noise due to the randomness of the number of secondary electrons or photons from the detection of a high-energy photon or particle.
Short wavelength infrared
synchronous shutter
Also called global shutter. A type of electronic shutter, where all pixels in the imager are sensitivity to light during exactly the same time span. Differs from the rolling shutter, where the instant of light sensitivity depends on the pixel's position in the image. further definitions:
pipelined, full, or true synchronous shutter, RWI: where the next image can be integrated during the readout of the previous one. snapshot, triggered or sequential synchronous shutter, ITR: where the light integration and readout are separated (alternating) in time.
Time Delay Integration: Mode of operation of an area CCD to obtain very high sensitivity when used as line scan device..
Frame time (1/fframe)
Transfer Gate. MOSFET gate or CCD electrode that acts as a switch preventing or allowing the transfer of (photo-) charge.
Total ionizing dose
integration time
Exposure time or electronic shutter time. The time span during which light is being converted to charge and accumulated in a pixel.
tape-out. In earlier days the (CAD-) design file was sent to the foundry or the mask shop on a magnetic tape. Today this goes via email or FTP.
Time of Flight: a nickname for ?distance ranging? or ?3D? cameras based on the capability of each pixel to measure the distance from the [camera + laser source] to any point in the scene by the time the light needs to travel form source via object to the imager. Often synonym of LIDAR.
Triple redundancy. Technique to make digital circuits SEU-hard
Benedictine monk, following the rule of the abbey of La Trappe. Later the beer brewed by these monks. Later the reward for finding a fatal error in the design of a CMOS image sensor. Later the name of such an error. . See also ?praline?
twin well
In a twin well CMOS process, there is of course the "real" well, but also an implant of opposite type to increase the doping level of the substrate. All recent CMOS processes are twin well. A ?triple well? is a twin well combination embedded in a lower doped ?tub?.
Uncorrelated Double Sampling, as opposed to CDS. See DS.
Image processing, typically on geographical images, estimating borders between homogenous colored patches, to a greater detail than the pixel resolution. A form of ?super-resolution?
Ultra Violet, EM radiation with wavelengths shorter than the visible light, typically the range 10nm to 400nm. In dermatology, the following sub-classification applies:
UVA: 315-400 nm UVB: 280-315 nm UVC: 100-280 nm
In astronomy and meteorology following terms have some traditional meaning:
XUV: 1-10 nm (X-ray UV) EUV: 10-100 nm (extreme UV) VUV: 100-200 nm (vacuum UV) DUV: less than 300 nm (deep UV)
Supply voltage of the polarity associated with "D", the drain of nMOSFETs. The general supply voltage of an integrated circuit. Typically 5, 3.3, 2.5, 1.8, 1.2, 1.0 and even lower volts referred to VSS. Alternatively the term VCC is used.
depletion voltage. The theoretical voltage that one would measure inside a pinned photodiode (PPD), at the point of full depletion, i.e. when the PPD is empty. Also called Vpinning.
Vacuum tube (CRT-) based image sensor.
Electrostatic Potential (-difference), but corrected for the material's work function and diffusion potentials, and is thus identical to the ?Fermi potential?. Is measured with a voltmeter. Reference, assigned to the value 0 V, is typically called ?ground? (GND).
pinning voltage
Other term for depletion voltage Vdep. See there.
Supply voltage of the polarity associated with "S", the source of nMOSFETs. Typically equal to GND. Also the term VEE is sometimes used.
Disk of silicon, sawn from an ?ingot? or monocrystal, on which ICs are fabricated.
Wafer Petanque
Sports discipline, created at the 1st Electroniad on 14 October 2016. Ressembles classic Petanque, yet is played by rolling wafers instead of throwing balls.
wavefront coding
Spatially/optically modulate the phase in the wavefront. In particular, the technique pioneered by CDM-optics to create TrueFocus, a technique that blurs the image with a constant amount irrespective the depth of field. After a subsequent digital sharpening step, the depth-of-field dependent unsharpness is absent. Thus creating an extended depth of focus/field in exchange of the S/N loss in de sharpening operation.
In Complementary MOS (CMOS), nMOSFETs and pMOSFETs cannot be placed in the same substrate. One of them must reside in an area of the opposite type as the substrate. In a p-type wafer the nMOSFETs are in the p-type substrate, and the pMOSFETs are in the n-type (n-)well.
A mode of operation of an image sensor, where only the pixels within a region of interest (ROI) are read out.
wonderbra image sensor
Sales demonstration of a mediocre quality image sensor, where the quality of the resulting images are "pushed up" by external means like image post-processing, defect hiding, etc.
In general the electromagnetic radiation with a wavelength (roughly) shorter than 1 nm. More specifically the radiation emerging from deceleration of electrons (Bremsstrahlung), which is the key difference with gamma rays (originating from nuclear reactions) or cosmic radiations (originating from astronomical objects).
Luma. As in YUV. See Luminance.
The ?Y? word, the key specification of any electronic (and other) component. The ratio of devices in spec (or actually used) over devices manufactured.
Scene illumination in [lx] whereby SNR=10:1, as measured on the Y (luma) channel.
Silent assumptions: after RGB demosaicing; smoothing and image processing not allowed; the scene is a large, homogenous, grey 18% reflectivity patch; the illuminant is a 6000K blackbody; the lens is a perfect f-number 2.8 lens.
Zero point something. Term used by Caeleste for pixels or image sensors that have a read noise far below 1 electronsRMS.
Electrostatic potential, [unit is J or eV]. Local property of a position in space. Energy that must be given to or taken from a hypothetical free unit charge to be stable at that certain position. The unit is [eV]. Is a relative measure, thus it must be referred to some "reference". In absence of any reference the reference is the potential in vacuum at an infinite distance. Ever tried?