|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Optical fiber lines and communication. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony In this regard, the infrastructure of communications through which data is transmitted is rapidly developing. In support of these words, the following figures can be cited - for the period from 1993 to 1998, the number of pages on the Internet increased from 50 to 50 million. In three years, from 1998 to 2001, the number of users connected to the Web increased from 143 to 700 million people. The growth of the computer park and the increase in the power of personal computer processors created a demand for large volumes of data transmission both over the Internet and over traditional communication lines: videophone, telephone, fax services. MAXIM's receiver/transmitter chipset that supports the above requirements allows optical/electrical conversions in SDH/SONET optical transmission systems. SDH is the European standard for high speed fiber optics. SONET is a standard that defines speeds, signals, and interfaces for synchronous data transmission at rates greater than one gigabit/sec. over a fiber-optic network. Network equipment manufacturers supply new products with improved parameters to the market. But the need for devices with higher data transfer performance is increasing. The speed of data transmission over copper wires has reached its limit, and a further increase is due to fiber optic cables. The physical nature of fiber optic cables can significantly expand the range of data transfer rates. Opportunities of fiber optic lines are used both in local networks and in extensive data networks between countries. Further expansion of these networks is expected to meet consumer demands for high-speed and high-quality information transmission. To transmit data through optical channels, the signals must be converted from electrical to optical, transmitted over a communication line, and then converted back to electrical at the receiver. These conversions take place in the transceiver device, which contains electronic components along with optical components. Fiber optic transceivers A time division multiplexer (TDM) widely used in transmission technology (a device that divides the access time to a high-speed channel between low-speed lines connected to the multiplexer), allows you to increase the transmission rate up to 10 Gb / s. Modern high-speed fiber optic systems offer the following transmission speed standards.
New methods of wavelength division multiplexing (WDM) or spectral division multiplexing make it possible to increase the data transmission density. To do this, multiple multiplex information streams are sent over a single fiber optic channel using each stream's transmission at different wavelengths. The electronic components in the WDM receiver and transmitter are different from those used in a time division system. Consider the operation of transceivers in an optical transmission system with time division TDM. Optical receivers Optical receivers detect the signals transmitted over the fiber optic cable and convert it into electrical signals, which then amplify and further reshape them, as well as clock signals. Depending on the baud rate and system specifics of the device, the data stream can be converted from serial to parallel. On fig. 1 shows the conversion, transmission and reception of a signal by a transceiver in serial or parallel form, as well as the formation of a clock signal.
A PIN photodiode (PIN) or an avalanche photodiode (APD) receive a light signal and, by modulating the electrical conductivity or changing the potential, make it possible to convert the received light signal into an electrical one. The PIN photodiode is a relatively cheap device and operates with the same supply voltage as the entire electronic device. However, its sensitivity is much less than that of an avalanche photodiode. Therefore, the distance between transmitter and receiver based on APD can be increased. Of course, all this is not free - APD photodiodes require (depending on the type) a supply voltage of 30 to 100 volts. In addition, the APD generates more noise, costs more than a PIN photodiode, and requires cooling. The signal from the photodetector is fed to a current controlled voltage amplifier (transimpedance amplifier - TIA). The asymmetric voltage received in the TIA is amplified and converted into a differential signal necessary for the operation of subsequent stages. The TIA must provide both high overload capacity and high input sensitivity (high dynamic range). Optical signals can be attenuated due to transmitter aging or a long communication link. Therefore, in order to increase the sensitivity of the TIA to a minimum, the self-noise must be reduced. On the other hand, a high overload capacity is required to avoid bit errors due to distortion from strong optical signals. The maximum achievable transconductance of the TIA amplifier depends on the operating frequency. In order to guarantee stability and the required bandwidth, the gain can only be optimized within a narrow range. With a low power optical signal, this limitation can make the output signal of the amplifier insufficient for further processing. In order to amplify small voltages in the range of 1 h 2 mV, another amplifier is placed after the TIA amplifier, which in most cases is a limiting amplifier (LA). This amplifier also includes a low signal indicator that alerts you when the incoming signal falls below a user-defined externally set threshold. So that when the signal is close to the threshold, the indicator flag does not change its value, the comparator is performed with hysteresis. The key component that follows the limiting amplifier in the receiver is the clock and data recovery (CDR) circuitry. The CDR performs the timing, decides on the amplitude level of the incoming signal, and outputs the time - and amplitude - of the recovered data stream. There are several ways to maintain the synchronization recovery function (external SAW filter, external control clock signal, etc.), but only an integrated approach can reduce both the cost and the amount of work. The International Telecommunication Union - Telecommunication standards sector (ITU - T) defines restrictions on admission, transmission and generation of oscillation. The signal quality at the output of the limiter amplifier is usually poor, mainly due to imperfect components in the optical transmission system. Because the CDR scheme must accept a certain amount of jitter in the input data to achieve normal, error-free operation, all receiver devices must comply with the ITU-T guidelines for jitter tolerance. In addition to jitter effects, noise and pulse distortion also reduce the phase of the control margin. This complicates the synchronization of the received information and reading the logic level of each bit. The use of a phase locked loop (PLL) system is an essential part in synchronizing the clock to the data stream to ensure that the clock signal is aligned with the middle of the information word. In order to further optimize the error bit rate (BER) for asymmetric rise and fall of received data signal transitions, the system must include a selection of clock-to-data phase control. The serial stream of recovered data and clocks from the CDR usually enters the serial-to-parallel conversion unit (deserializer). Its conversion speed depends on the bit rate and compatibility (in terms of speed) with CMOS system components. Optical transmitter An optical transmitter in a fiber optic system converts the electrical data sequence supplied by the CMOS components of the system into an optical data stream. As shown in fig. 1, the transmitter consists of a parallel-to-serial converter with a clock synthesizer (which depends on the system setting and bit rate), a driver, and an optical signal source. For the transmission of information over a fiber optic channel, two important wavelength ranges are used: 1000 h 1300 nm, called the second optical window, and 1500 h 1800 nm, known as the third optical window. On these ranges - the smallest signal loss in the line per unit cable length (dB / km). Various optical sources can be used for optical transmission systems. For example, light emitting diodes (LEDs) are often used in low cost local area networks for short distance communications. However, a wide spectral bandwidth and the impossibility of working in the wavelengths of the second and third optical windows do not allow the use of the LED in telecommunication systems! Unlike an LED, an optically modulated laser transmitter with high spectral purity can operate in a third optical window. Therefore, for ultra long distance and WDM transmission systems, where cost is not the main consideration, but high performance is a must, a laser optical source is used. For optical communication links, various types of direct-simulated semiconductor laser diodes have an optimal cost/performance ratio for short, medium and long transmissions. The devices can operate in both the second and third optical windows. All semiconductor laser diodes used for direct modulation typically have a DC bias current requirement to set the operating point and modulation current for signal transmission. The amount of bias current and modulation current depends on the characteristics of the laser diode and may differ from type to type and from each other within the same type. The range of these characteristics over time and temperature must be taken into account when designing the transmitter unit. This is especially true for economically more profitable uncooled types of semiconductor lasers. It follows that the laser driver must provide a bias current and modulation current in a range sufficient to allow different optical transmitters with a wide choice of laser diodes to operate for a long time and at different temperatures. To compensate for the deteriorating performance of the laser diode, an automatic power control (APC) device is used. It uses a photodiode that converts the light energy of the laser into a proportional current and supplies it to the laser driver. Based on this signal, the driver outputs a bias current to the laser diode so that the light output remains constant and matches the original setting. This maintains the "amplitude" of the optical signal. The photodiode found in the APC circuit can also be used in automatic modulation control (AMC). In addition to these functions, the system must be able to stop laser transmissions by blocking the driver, but the reception of data at the input must not be interrupted. By adding a flip-flop or latch (as part of a laser driver or parallel-to-serial converter), oscillation efficiency can be improved by re-timing this data stream before it reaches the output of the laser diode driver. Clock recovery and serialization require clock pulses to be synthesized. This synthesizer can also be integrated into a parallel-to-serial converter and usually includes a phase locked loop circuit. The synthesizer must guarantee data transmission with as little jitter as possible. As a result, the synthesizer plays a key role in the transmitter of an optical communication system. On fig. 2 and 3 show the synchronous transport modules (STM4) of the receiver and transmitter, respectively.
As mentioned above, all components of an optical system for telecommunications must comply with ITU - T recommendations. The chipset produced by MAXIM allows designers to develop competitive transceiver devices. All products are based on high-speed bipolar technology, when the transmission frequency for p-n-p transistor is 6,4 GHz, and for n-p-n - 8,7 GHz. For a submicron bipolar process, the transmission frequency of the npn transistor is 27 GHz. The ICs for STM 4 that are being produced use +3,3V power supplies. Preamp The TIA amplifier (MAX 3664) converts the asymmetric current from the photodiode sensor into an asymmetric voltage, which is amplified and converted into a differential signal. With an input current of 100 A (p-p), the output has differential oscillations of up to 900 mV (p-p). Low input noise is achieved by careful IC design and by limiting the bandwidth to 590 MHz with an input capacitance of 1,1 pF. When using a single low noise pin diode, typical input sensitivity corresponds to -32 dBm optical power. With a 3,3 V supply, the power consumption is only 85 mW. Data synchronization and recovery (CDR) The MAX 3675 chip must recover the clock signals from the received data stream and their clocking. The two ICs MAX 3664 and MAX 3675 form the basis of the receiver's optoelectronic module, while power consumption is less than 300mW at 3,3V. The analog input sensitivity is 3 mV peak-to-peak. The blocking loss alarm function and the input signal power sensor are combined with the limiting amplifier. The power sensor on the RSSI pin - an indicator of the strength of the received signal - outputs a voltage proportional to the input power. The phase-locked loop circuitry required for clock recovery is also fully integrated into the MAX 3675 and does not require an external clock reference. Serial to Parallel Conversion Unit (DEMUX) To work with various system interface schemes, MAXIM offers the MAX 3680 and MAX 3681 serial-to-parallel converters. The MAX 3680 converts a 622 Mbps serial data stream to a 78 Mbps eight-bit word stream. Data and clock output is TTL compatible. Power consumption - 165 mW when powered by 3,3V. The MAX 3681 converts a serial data stream (622 Mbps) to a 155 Mbps four-bit word stream. Its differential data and clock support have a low voltage differential signal (LVDS). Power consumption - 265 mW at 3,3V supply. By driving through the SINC pin, you can slightly tune the data output relative to the clock signal. Parallel to Serial Converter (MUX) The MAX3691 chip converts four 155 Mbps LVDS data streams to a 622 Mbps serial stream. The necessary transmit clock is synthesized using an onboard phase locked loop including a voltage controlled oscillator, a loop filter amplifier and a phase detector that requires only external clock references. With a power supply of 3,3V, the power consumption is 215 mW. The serial data output is provided by positive emitter-coupled logic differential level (PECL) signals. Laser shaper (LD) The main task of the LD (MAX 3667) is to supply bias current and modulating current for direct modulation of the laser diode. For flexibility, the differential inputs accept PECL data streams as well as differential voltage swings up to 320mV peak-to-peak at Vcc = 0,75V. By changing the external resistor between the BIASSET pin and ground, the bias current can be adjusted from 5 to 90 mA, and the modulation current can be adjusted from 5 to 60 mA by changing the resistor between the MODSET pin and ground. An internal, temperature-stabilized voltage reference guarantees stable bias and modulation currents. To avoid damaging the MAX 3667, the BIASSET, MODSET, and APCSET pins must not be grounded. An internal safety circuit limits the total output current to approximately 150 mA. The MAX 3667 requires a single 3,3V power supply to operate. As an alternative to the MAX 3667, the MAX 3766 five-volt laser driver is available with data rates from 155 Mbps to 1,25 Gbps. The MAX 3766 includes all the attributes mentioned for the MAX 3667 but with a wider bandwidth. This IC has extended laser safety conditions, and with a single external resistor, "optical amplitude" is maintained as temperature and laser slope change. This article presents a comprehensive solution by MAXIM for an optical transceiver. You can view the range of manufactured devices for optical / electrical assemblies and their characteristics at maxim-ic.com. There you can also get acquainted with the technical parameters of 98 basic devices used in electronic units of fiber optic communication. A fairly detailed selection of materials in Russian about the products manufactured by MAXIM can be found on the website rtcs.ru, Rainbow Technologies, the official distributor of MAXIM in the CIS countries. Author: A. Shitikov, ashitikov@rainbow.msk.ru; Publication: radioradar.net
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Drugs will be tested on a human simulator ▪ Implementation of the C-V2X vehicular communication system
▪ site section Frequency synthesizers. Selection of articles ▪ Philistine article. Popular expression ▪ Article Lovage officinalis. Legends, cultivation, methods of application ▪ article at the end. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page