I2C Bus History

I2C bus history was started in 1992, when Philips company released its first specification version 1.0. This specification precluded the setting of the slave device address programmatically as the most difficult procedure. Along with the standard mode data transfering rates of 100 kbit/s (low-speed), fast transfer mode (fast-speed) was introduced with speeds up to 400 kbit/s. 1O-bit addressing mode has been appeared also.
Version 2.0 was released in 1998 and introduced a high-speed bus specification mode (Hs-mode) with a transfer rate up to 3.4 Mbit/s. And there were requirements for compatibility with low-speed and fast-speed modes. By the time when version 2.0 has been appeared, I2C bus has been spread worldwide, becoming an international standard. There were developed more than 1000 integrated circuits, the official license for using specifications, was acquired by more than 50 companies. Version 2.1, which is dated by 2000, includes minor modifications which are not reflected in version 2.0. At the time of this writing, version 2.1 is the latest valid version released by Phillips.

Signal Transmission Devices Review. Prt.6 Telephone lines and computer networks

Telephone lines has been used as a TV-signals transfer medium for a long time. This type of system works on the slow-scan television principle with the use of sender-receiver modems. Because of the low possibilities of the telecommunication line pass band (just 3 kHz), the telecommunication line The signal is wrote down to the buffer at the receiving part of the system and then read line by line and transmitted to the channel. That is why the signal gets to the receiver part slowly and it is absolutely impossible to transfer in real time. There are some devices which increase the transfer speed of shots – special modems and TV images hardware compression devices. It is possible to reduce the transfer speed of shots with a keyframe transfer slowing and a quick transferring of a frame-to-frame difference. This principle is usually used in observation systems. The signal on-line transferring with a quite good image quality is possible, thanks to the software compression methods, which are developed now.

Local computer networks are also wide used to transfer video signals. In this type of data transmission systems digital cameras with built in modems and mini-servers are used. File creating proceeds by modern compressing methods. These systems are used for closed-circuit television systems, where it is necessary to display images from all watching cameras on a screen in on-line mode. A special software allows to regulate the speed of shot transferring and to set the image resolutions.

Signal Transmission Devices Review. Prt.5 Wireless links

Sometimes, the laying of signal transmitting terrestrial channel is too difficult, and in some instances (at the uplands or at sparsely neighboured places, for example) it is economically unviable.

In these cases, radio relay equipment is the best solving. The requirement of it is an optical visibility of a receiving antenna and a transmitting antenna. The transmission range depends on its frequency: more higher frequency – the less of a range.

A radio relay equipment package usually includes a frequency-division multiplex module, which allows a transmission of a few signals in one communication line.

If the transmission range is small enough, it is possible to use atmospheric optical lines. A TV-signal, transformed by transmission equipment, transforms in a powerful luminous flux, which comes on the receiving equipment through the atmosphere.

The concept is looks like a FOCL concept. But a high-precise optics is used here to form a straight optic beam. It allows to make the receiving leaks lower. The transmission range of this system is not so big – 1500 m, and the operational reliability absolutely depends on atmospheric phenomenons.

That is why the signal may disappear if there is a thick fog.

Signal Transmission Devices Review. Prt.4 Fiber-optic cable (FOC)

This type of cables is the most effective transmission media. Comparably to other communication lines. FOC has some advantages:

vast signal transmitting distance, low leakage;

broad signal transmitting frequency band;

freedom from electromagnetic noise;

ground loop has no effect on it;

protected from external access;

high level of safe use in rooms with risk of fire and explosion based on its physical structure.

Fiber-optic communication lines allow to create multitasking nets and can be used for varied aims: as a system of data transferring in the cable television, in telephony, in guard systems.

FOC consists of a central load-bearing member, around which optical fiber located. It is sheathed and has load-bearing unit. Installing FOC can take place at different conditions, so that different constructive variants of FOC exist:

ropes are used for air lines;

armored cables are used for underlaying of cable;

moistureproof FOC – for cable laying in the water.

It is also necessary to meet technical requirements that are described in the FOC-manufacturer instruction during the installation and construction work, especially point about a cable bend radius and maximum cable stretching.

Optical fiber has a central light conductor with high refraction index. The conductor is enclosed from outside, and the shell has a low refraction index. It helps the light ray to reflect from the shell without getting out from it. According to the refraction index optical fiber can be divided in two main groups: multimode and monomode cables. Several rays of light pass through the inner conductor in one time. The rays reflect from the outer conductor at various angles. The monomode cable inner conductor has a small diameter, which is commensurable with the transmitted wave length. That is why the light rays passing along the led lamp longitudinal axis and have no reflection from outer conductor.

Every fiber-optic information transfer scheme consists of next elements:

signal source;

modulator-amplifier in conjunction with laser and photodiode emitter. LED radiates a wide spectrum light at a wide angle in several different directions . It is used in multimode cables. The laser emitter has a high power, a tight angle of light feeding and generates a one-length wave light;

fiber-optic cable as a signal transmission medium;

an photodiode at the receiving side and a booster;

The monomode cable has the balance of advantage over the multimode cable. Its service band is twice wider, higher transmission range and less of losses. Though the price of the facility is much more higher, so it’s recommended to use multimode cable at the FOCL sections, with the length less than 10 km. It is necessary to remember about the losses at the supply splits and optical splices during the cable tracks design calculations, because the every jointing brings a signal attenuation, the rate of which depends on professionalism of the staff. The fiber has a heterogeneous structure, which is also needed to be taken into account when the distance calculating.

Signal Transmission Devices Review. Prt.3 Crossover cable

The concept of signal transmission by crossover cable consists in asymmetrical signal to symmetrical one transformation and bidirectional signal transmitting.

The symmetrical transmission method consists in equalization equipment installation at the receiving site. This receiver modifies an asymmetric signal into symmetric one, that allows to increase the noise security level during the transmission of a few different signal types by one multi-pair cable. For example, audio and video signals transmitting, telephony, etc. Opposite to coaxial cable, in crossover cables the external electromagnetic noise effects on both conductors at the same time. As is well known, the received signal is antipodal, and the interference is inphase, that is why the interference is automatically suppressed by a signal booster, which is equipped with differential input. It stands to mention, that it is much more cheaper to install and support systems, where multi-pair cable are used, in opposite to similar projects, based on coaxial cables. The labour intensity is much more lower in this case. In addition, the cable system of crossover type is not so cluttered, pawn elements have tinner sectional view, less wiring ducts are needed.

It is possible to create a project with an overcapacity: just leave spare wires in multi-pair and use it as and when necessary. There is a wide variety of TV-signal transfer devices by crossover cable and cross-functional kits, which can conform to every length an type of communication lines. It is necessary to remember, that the unshielded twisted pair is more effective, because the shielded cable is very exposed to the influence of a shield parasitic capacitance, which decrease maximum range of TV-signal transmission in twice.

The most important moment of TV-signal transmission by crossover cables is a fine-tuning of transmitter-receiver equipment, which is the thing the receivable signal quality depends on. A special television signal test-generator, which forms a test card (also known as a test pattern). It helps to adjust the amplitude-frequency characteristic of crossover cable and to remove the frequency distortions.

It is necessary to remember about a built lightning guard while choosing the TV-signal transmitter-receiver equipment. Output stages of transmitting sets and input stages of receiving sets may break down because of electric impulse leakage. That’s why the lightning guard is a necessary factor to avoid permanent repairs of burned-out facility. To tap-off static discharges it is necessary to connect the receiver and transmitter to a ground component, while the grounding system installing.

Signal Transmission Devices Review. Prt.2 Coaxial cables

Background interference is not the only trouble for the coaxial cable. In case of thunderhead, static discharges can appear in the shield or the center conductor. The difference of potentials between a metallic elements of transmission and receiving equipment and a cable armour comes up to a value of a few hundreds volts. Though this effect is short-run, it can disable the equipment, which costs a lot of money. To prevent this situation, it is necessary to implement the lightning guard systems. They are installed on transmitting and receiving cable sides and acts as a ground shunt for spurious pulses, which appear appear in the shield or the center conductor.

During the signal transmitting through the long mileage coaxial cable, amplitude-phase frequency distortions appear. The distortion level depends on the cable characteristic. Summary ohmic resistor of the center conductor and its shield makes the cable exit-signal amplitude decrease. This and the influencing of the capacitive component of coaxial cable leads to the substantial decrease of a signal on a high frequency. Besides, capacitance components of a cable impedance lead to the signal phase distortion at the cable output. As a result, the image definition and contrast are decrease, the color rendering is distorted and a color even can absolutely disappear. It is possible, that the signal will be distorted, because electromagnetic fields and noises can take an effect if a long mileage coaxial cable is used. It is impossible to do without extra equipment in this case. For example, the boosters, which compensate the signal losses and correct the amplitude-frequency and phase-frequency response characteristics.

Signal Transmission Devices Review. Prt.1 Coaxial Cables

Selection of TV signals transmission lines is very important in realizations of diverse projects, because the quality of receivable TV image depends on the communication lines specifications. There are several signal transfer mediums: twisted cables, coaxial and fiber-optic cables, wireless and telephone communication lines, computer networks. Each one will be overviewed.

Coaxial Cable

Coaxial cable is the most widespread transmission facility of TV signals. It belongs to the nonsymmetrical communication line category and contains a center conductor, dielectric material and armour. The signal transmitted over the central conductor, and the armour is a shield. External interferences, induced by the armour, are grounded. This way, the level of cables external interferences amenability depends on the armour stiffness. Coaxial cables armour can be twisted or foiled. The cable with twisted shield usually used in security and video control systems, because it is more resistant to external interferences.

Foiled coaxial cable doesn’t used in the security TV, so it is susceptible to low-frequency interferences. This kind of cables are wide used in cable TV, where the signal transmits by subcarrier frequency. During a coaxial cable assembly, it is necessary to remember about a probability of leakages appearance in places, where the electric cables lay close enough. It is also needed to take into account that the foreign ground currents may appear while signals passing through the center conductor. It happens when the receiving and transmitting equipments are connected to diverse electric supply phases or grounding points. This problem comes out in image deformation as a consequence of background interferences attack. There also may be an image loss of synchronization.

Background interferences can be removed in a very easy way – by isolation transformer installation. It is set into a coaxial line break on the receiving side. The effect evolves because of a break in a interference circuit in the center conductor and a shielded part. Foreign ground current discontinues and background interferences disappear. Though, the isolation transformers have a disadvantage: the signal bandwidth is unsteady. That’s why the most effective way of the frequency interference removing is galvanic isolation devices installing, which are used on the base of an optoelectronic transducer. Besides, the devices enable to neutralize electromagnetic blasts with network wide frequency of 50 Hz.

About FOCL And Analog Transmission Prt.4

Fiber absorption loss. It is connected with transformation of one type of energy to another. Electromagnetic wave with defined length cause the changing of electron orbit in some chemical elements, and that leads to the fiber heating. Obviously, the wave absorption process as fast, as the wave is short and the fiber material is pure.

Dispersion losses. The cause of the signal power loss is that a part of a light flux comes out of a wave-propagating system. It is based on imperfections of the material refraction index. The dispersion losses increase when the the wavelength decrease.

In theory, it is possible to reach better rates of common attenuation at the intersection of absorption and spreading curves. The reality is more complicated and connected with the chemical composition of the environment. In quartz fiber (SiO2) silicon and oxygen become active when the length of the wave reaches defined value and very impair the transmission capacity.

As a result, three low-loss transmission windows appear , where the attenuation has the minimal value. The most common values of wavelength is: 0.85; 1.3; 1.55; mkm.

For the analog transmission use waves with length 850 and 1310 mkm.

Special heterojunction laser was created for these diapasons, and modern FOCL are based on it.

Nowadays, fiber-optic with such specifications is considered to be out-dated. The output of AllWave ZWP fiber-optic has been mastered long time ago. In this fiber-optic type hydroxyl ions were removed from the silica glass composition. This glass has not a window, but an aperture with diapason 1300 – 1600 nm.

All the low-loss transmission windows are laying in infra-red, i.e. the light, which is transmitted in the FOCL, is invisible for the men’s eye. It is worth noting that it is possible to add visible light into the standard fiber-optic. Small blocks, which can be found in some reflectometer, are used for this reason. Also, a little converted laser pointer can be used for the same thing. With the help of these devices it is possible to find cord breaks. At the place, where the fiber-optic is broken, will be a bright shine. This kind of light is usable in a short distances (1 km maximum) because it is fading fast in the fiber.

About FOCL And Analog Transmission Prt.3

Physical Properties of Optical Fiber

All common types of fibers are characterized by two the most important properties: attenuation and dispersion.

There are modal and material dispersion – distortion of a signal, which caused by specialty of light-wave propagation.

Material dispersion appears because of the speed difference between waves with diverse length, which is based on specialty of physical structure of fiber. This effect particularly noticeable while singlemode optical fiber using. Reduction of emission bandwidth of the source and optimal wave-length selection decrease the material dispersion.

Modal dispersion appears in multimode fiber because of different length of the path, that the various mod light rays go through. Reduction of the fiber core diameter and mode numbers, using fiber with gradient profile help to reduce this dispersion.

An attenuation of the signal in the fiber optic cable depends on the material properties and environments. Attenuation characterizes the power loss of transmitted signal over defined distance. It is measured in dB/km, where decibel is a logarithmic relation expression of power, that comes out from source P1, to power, that comes into receiver P2, dB=10*log(P1/P2). The leak of 3 dB means that the half of power is lost. The leak of 10 dB means that only 1/10 of source power gets to the receiver.

Usually, fiber-optic lines can normally work with leak of 30 dB (taking 1/1000 of power).

There are two radically different physical mechanisms, which lead to this effect: fiber absorption loss and dispersion loss. The effects will be describe in the next article.


About FOCL And Analog Transmission Prt.2

How FOCL Works

The fiber-optics is a technology, in which light is used as a data medium and it doesn’t matter what kind of information it is: analog or digital one. The infra-light is used in it, and the communication environment is a fiberglass.

Fiber-optic facilities can be used for different types analog or digital signals transmitting.

In the most simple form the fiber-optic line consists of three components:

– fiber-optic transmitter is for incoming electrical signal from a source to modulated light conversion

– fiber-optic line, which broadcast signals to the receiver

– fiber-optic receiver, which converse signals into electrical (almost identical to the source signal)

The source of fiber-optic inside light is LED (or LD). A special receiving detector one the opposite end of cable converses light signals into electrical.

The fiber-oprics is based on a special effect – deflection with maximum angle of incidence, when a pure reflection takes place. This effect appears when a ray of light comes out from a dense medium and gets into a less dense medium in a defined angle. Inner conductor of a fiber optic cable has a higher refractive index than the cable sheath. This way the ray of light, that coming through the inner conductor, can’t gets out of the conductor because of the pure reflection effect (pic.1). As a result, a transmitted signal moves inside of a closed environment and travels form a transmitter to a receiver.

Pic.1 Pure reflection effect

Others components of the cable protect the brittle fiber from a damage that hostile environment can bring.