LBCAST
Encyclopedia
LBCAST is a type of photo sensor which the manufacturer claims is simpler and thus smaller and faster than CMOS sensors. It was developed over ten years by Nikon
, in parallel with other manufacturer's development of CMOS, and resulted in shipping product in 2003.
Both CMOS and LBCAST technologies branched from researchers discussions of "amplifying sensors" as a way to develop an imaging sensor with lower power requirements than the already-existing CCD
sensor technology, for use in portable devices such as DSLR cameras.
From the Nikon Website:
and the D2Hs were the only publicly available cameras known to carry the sensor. Nikon has opted to use CCDs sourced from Sony in most of their low and mid range cameras and used a CMOS sensor in the flagship D2Xs/D2x. The LBCAST sensor in the D2Hs has remained at 4.1MP.
With the advent of the D3, D700 and D300 cameras in 2007 and 2008, all featuring CMOS sensor technology, it is unknown whether LBCAST plays a part in the design of the CMOS sensor of either, since Nikon's implementation of LBCAST is an adaptation of CMOS, and it is therefore not technically incorrect to refer to the known instances of LBCAST as CMOS, Nikon has not been forthcoming to requests for specific information on the D3 sensor and Nikon have claimed in the past that LBCAST would be further developed.
Nikon
, also known as just Nikon, is a multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging. Its products include cameras, binoculars, microscopes, measurement instruments, and the steppers used in the photolithography steps of semiconductor fabrication, of which...
, in parallel with other manufacturer's development of CMOS, and resulted in shipping product in 2003.
Both CMOS and LBCAST technologies branched from researchers discussions of "amplifying sensors" as a way to develop an imaging sensor with lower power requirements than the already-existing CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
sensor technology, for use in portable devices such as DSLR cameras.
From the Nikon Website:
- "In July 2003, Nikon introduced LBCAST- a completely new type of image sensor, different from CCD and CMOS, that is a high-speed, power-efficient, low-noise device to be installed in Nikon's flagship camera, the D2Hs."
- "... Compared with conventional sensors, it saves more power and achieves less dark noise. (Dark noise is a phenomenon in which randomly spaced bright pixels appear in images due to the heat from the image device during shooting). Also, LBCAST increases image processing speed and improves sensitivity, contrast and color reproduction."
Comparison between LBCAST and CMOS photo sensors
The main differences between LBCAST and CMOS-based sensors appear to be those given below:- LBCAST divides the photosites to be read out into two channels by colour, redRedRed is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
and blueBlueBlue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...
photosites—making up 50% of the total number of photosites between them, as in CMOS and CCD colour sensors—accumulate using one read-channel, while green photosites—which make up the other 50% of total pixels, as in CMOS and CCD—accumulate in a dedicated channel.
- This division is to speed reading, and the separation of green pixels, to which the human eyeHuman eyeThe human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
is most sensitive, reduces noise artifacts which might otherwise be introduced by residual electrical charge in the accumulation circuitElectronic circuitAn electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...
ry, acquired previously from reading a pixel of a different colour.
- Red and blue are significantly less important in human sight, and so presumably a decision was made not to keep separate read channels for the two colours, in order to simplify the circuit design for practical use -- at least in the described version of LBCAST technology.
- Each photosite in LBCAST uses a single JFETJFETThe junction gate field-effect transistor is the simplest type of field-effect transistor. It can be used as an electronically-controlled switch or as a voltage-controlled resistance. Electric charge flows through a semiconducting channel between "source" and "drain" terminals...
transistorTransistorA transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
in place of two MOSFETMOSFETThe metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
transistors used for the separate tasks of photosite read-out selection and signal amplification, in CMOS technology. In total, CMOS uses four transistors per photosite, where LBCAST manages with three.
- Charge to be (re-)distributed between components in the sensor during use are channeled via the LBCAST lower layers, where CMOS channels this charge over the surface layer. This difference is also claimed to reduce the presence of noise artifacts.
- The simpler circuitry required translates into more space for lightLightLight or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
to be received, since wiring and opaque masking takes less space.
- The simpler circuitry required translates into fewer layers of material in the silicon chipSilicon ChipSilicon Chip is an Australian electronics magazine. It was started in November, 1987 by Leo Simpson. Following the demise of Electronics Australia, it is the only hobbyist-related electronics magazine remaining in Australia.- Magazine :...
meaning that tangential light requires less correction in order to traverse to the depth at which the photons result in signalSignal (electrical engineering)In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time-varying or spatial-varying quantity....
, simplifying the need for lensingMicrolensA microlens is a small lens, generally with a diameter less than a millimetre and often as small as 10 micrometres . The small sizes of the lenses means that a simple design can give good optical quality but sometimes unwanted effects arise due to optical diffraction at the small features...
at each pixel or photosite, and therefore theoretically, attaining greater image uniformity.
Uses of LBCAST sensors
As at end 2006, the Nikon D2HNikon D2H
The Nikon D2H is a professional-grade digital single-lens reflex camera introduced by Nikon Corporation on July 22, 2003. It uses Nikon's own JFET-LBCAST sensor with a 4.1 megapixel resolution, and is optimised for sports and action shooting that require a high frame rate. In 2005, the D2H was...
and the D2Hs were the only publicly available cameras known to carry the sensor. Nikon has opted to use CCDs sourced from Sony in most of their low and mid range cameras and used a CMOS sensor in the flagship D2Xs/D2x. The LBCAST sensor in the D2Hs has remained at 4.1MP.
With the advent of the D3, D700 and D300 cameras in 2007 and 2008, all featuring CMOS sensor technology, it is unknown whether LBCAST plays a part in the design of the CMOS sensor of either, since Nikon's implementation of LBCAST is an adaptation of CMOS, and it is therefore not technically incorrect to refer to the known instances of LBCAST as CMOS, Nikon has not been forthcoming to requests for specific information on the D3 sensor and Nikon have claimed in the past that LBCAST would be further developed.
Criticisms of LBCAST sensors
The following weaknesses have been cited as affecting the Nikon D2H, although whether these issues have origins specific to LBCAST, and whether LBCAST necessitates these problems, is not known.- Colour castColour castA colour cast is a tint of a particular colour, usually unwanted, which affects the whole of a photographic image evenly.Certain types of light can cause film and digital cameras to have a colour cast...
-- generally (and by definition) colour correction is a fundamental requirement of imaging in any medium where incident light quality is variable, including unaided human vision, and so this possibly a software issue.
- Infra-red pollution—incident infra-red light is usually filtered on image sensors, using a specific thin film dedicated to this task (but which may serve an additional purpose in protecting the relatively much more expensive sensor component from contamination and damage), and so this issue, if truly the result of ir pollution, may be a problem which is independent of the LBCAST technology of the sensor.
- Low resolution -- it is not known whether the relatively low resolution of the D2H and D2Hs in comparison with other professional cameras of the day is a technological limitation of LBCAST, a business management or marketingMarketingMarketing is the process used to determine what products or services may be of interest to customers, and the strategy to use in sales, communications and business development. It generates the strategy that underlies sales techniques, business communication, and business developments...
decision, or whether it has other causes such as gradual ramping-up of manufacturing capability of a new technology by Nikon, who did not appear previously to have the capacity to have novel sensors manufactured to their specification. It is known that there is a market for high-speed, power efficient cameras where higher resolution is not required, for example newspaper journalismPhotojournalismPhotojournalism is a particular form of journalism that creates images in order to tell a news story. It is now usually understood to refer only to still images, but in some cases the term also refers to video used in broadcast journalism...
.