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Self-clocking
In telecommunications and electronics, a self-clocking signal is one that can be decoded without the need for a separate clock signal or other source of synchronization. This is usually done by including embedded synchronization information within the signal, and adding constraints on the coding of the data payload such that false synchronization can easily be detected. Most line codes are designed to be self-clocking. Isochronicity and anisochronicity If a clock signal is embedded in the data transmission, there are two possibilities: the clock signals are sent at the same time as the data (isochronous), or at a different time ( anisochronous). Isochronous self-clocking signals If the embedded clock signal is isochronous, it gets sent simultaneously with the data. Below is an example signal, in this case using the Manchester code self-clocking signal. The data and clock cycles can be thought of as "adding up" to a combination, where both the clock cycle and the data can be retr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Manchester Code
In telecommunication and data storage, Manchester code (also known as phase encoding, or PE) is a line code in which the encoding of each data bit is either low then high, or high then low, for equal time. It is a self-clocking signal with no DC component. Consequently, electrical connections using a Manchester code are easily galvanically isolated. Manchester code derives its name from its development at the University of Manchester, where the coding was used for storing data on the magnetic drums of the Manchester Mark 1 computer. Manchester code was widely used for magnetic recording on 1600 bpi computer tapes before the introduction of 6250 bpi tapes which used the more efficient group-coded recording. Manchester code was used in early Ethernet physical layer standards and is still used in consumer IR protocols, RFID and near-field communication. Features Manchester coding is a special case of binary phase-shift keying (BPSK), where the data controls the pha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Delay Insensitive Circuit
A delay-insensitive circuit is a type of asynchronous circuit which performs a digital logic operation often within a computing processor chip. Instead of using clock signals or other global control signals, the sequencing of computation in delay-insensitive circuit is determined by the data flow. Data flows from one circuit element to another using "handshakes", or sequences of voltage transitions to indicate readiness to receive data, or readiness to offer data. Typically, inputs of a circuit module will indicate their readiness to receive, which will be "acknowledged" by the connected output by sending data (encoded in such a way that the receiver can detect the validity directly), and once that data has been safely received, the receiver will explicitly acknowledge it, allowing the sender to remove the data, thus completing the handshake, and allowing another datum to be transmitted. In a delay-insensitive circuit, there is therefore no need to provide a clock signal to deter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-synchronizing Code
In coding theory, especially in telecommunications, a self-synchronizing code is a uniquely decodable code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a valid code word. Put another way, a set of strings (called "code words") over an alphabet is called a self-synchronizing code if for each string obtained by concatenating two code words, the substring starting at the second symbol and ending at the second-last symbol does not contain any code word as substring. Every self-synchronizing code is a prefix code, but not all prefix codes are self-synchronizing. Other terms for self-synchronizing code are synchronized codeBerstel et al (2010) p. 137 or, ambiguously, comma-free code.Berstel & Perrin (1985) p. 377 A self-synchronizing code permits the proper framing of transmitted code words provided that no uncorrected errors occur in the symbol stream; external synchronization is not required. Se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bit Slip
In digital transmission, bit slip is the loss or gain of a bit or bits, caused by clock drift – variations in the respective clock rates of the transmitting and receiving devices. One cause of bit slippage is overflow of a receive buffer that occurs when the transmitter's clock rate exceeds that of the receiver. This causes one or more bits to be dropped for lack of storage capacity. One way to maintain timing between transmitting and receiving devices is to employ an asynchronous protocol such as start-stop. Alternatively, bit slip can be prevented by using a self-clocking signal (such as a signal modulated using OQPSK) or using a line coding such as Manchester encoding. Another cause is "losing count", as on a hard drive: if a hard drive encounters a long string of 0s, without any 1s (or a string of 1s without 0s), it may lose track of the frame between fields, and suffer bit slip. When a pulse of N consecutive zero bits are sent, clock drift may cause the hardware to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
4B5B
In telecommunication, 4B5B is a form of data communications line code. 4B5B maps groups of 4 bits of data onto groups of 5 bits for transmission. These 5-bit words are pre-determined in a dictionary and they are chosen to ensure that there will be sufficient transitions in the line state to produce a self-clocking signal. A collateral effect of the code is that 25% more bits are needed to send the same information. An alternative to using 4B5B coding is to use a scrambler. Some systems use scramblers in conjunction with 4B5B coding to assure DC balance and improve electromagnetic compatibility. Depending on the standard or specification of interest, there may be several 5-bit output codes left unused. The presence of any of the unused codes in the data stream can be used as an indication that there is a fault somewhere in the link. Therefore, the unused codes can be used to detect errors in the data stream. Applications 4B5B was popularized by fiber distributed data interfa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasible with the human voice, but with a similar scale of expediency; thus, slow systems (such as postal mail) are excluded from the field. The transmission media in telecommunication have evolved through numerous stages of technology, from beacons and other visual signals (such as smoke signals, semaphore telegraphs, signal flags, and optical heliographs), to electrical cable and electromagnetic radiation, including light. Such transmission paths are often divided into communication channels, which afford the advantages of multiplexing multiple concurrent communication sessions. ''Telecommunication'' is often used in its plural form. Other examples of pre-modern long-distance communication included audio messages, such as coded drumb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anisochronous
In telecommunication, the term anisochronous refers to a periodic signal, pertaining to transmission in which the time interval separating any two corresponding transitions is not necessarily related to the time interval separating any other two transitions. It can also pertain to a data transmission in which there is always a whole number of unit intervals between any two significant instants in the same block or character, but not between significant instants in different blocks or characters. In practice, anisochronous typically means that data packets are not arriving in the same order they were transmitted, thus dramatically altering the quality of a multimedia transmission (e.g. voice, video, music), or after processing to restore isochronicity, have had significant amounts of latency added. Isochronous and anisochronous are characteristics, while synchronous Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clock Drift
Clock drift refers to several related phenomena where a clock does not run at exactly the same rate as a reference clock. That is, after some time the clock "drifts apart" or gradually desynchronizes from the other clock. All clocks are subject to drift, causing eventual divergence unless resynchronized. In particular, the drift of crystal-based clocks used in computers requires some synchronization mechanism for any high-speed communication. Computer clock drift can be utilized to build random number generators. These can however be exploited by timing attacks. In non-atomic clocks Everyday clocks such as wristwatches have finite precision. Eventually they require correction to remain accurate. The rate of drift depends on the clock's quality, sometimes the stability of the power source, the ambient temperature, and other subtle environmental variables. Thus the same clock can have different drift rates at different occasions. More advanced clocks and old mechanical clocks ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quadrature Modulation
Quadrature may refer to: In signal processing: *Quadrature amplitude modulation (QAM), a modulation method of using both an (in-phase) carrier wave and a 'quadrature' carrier wave that is 90° out of phase with the main, or in-phase, carrier *Quadrature phase, oscillations that are said to be ''in quadrature'' if they are separated in phase by 90° (/2, or /4) * Quadrature filter, the analytic signal of a real-valued filter *Quadrature phase-shift keying (QPSK), a phase-shift keying of using four quadrate points on the constellation diagram, equispaced around a circle In mathematics: * Quadrature (mathematics), drawing a square with the same area as a given plane figure (''squaring'') or computing that area ** Quadrature of the circle * Numerical integration is often called 'numerical quadrature' or simply 'quadrature' ** Gaussian quadrature, a special case of numerical integration * Formerly, a synonym for "integral" ** Integral ** Antiderivative * Addition in quadrature, combini ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polar Modulation
Polar modulation is analogous to quadrature modulation in the same way that polar coordinates are analogous to Cartesian coordinates. Quadrature modulation makes use of Cartesian coordinates, ''x'' and ''y''. When considering quadrature modulation, the ''x'' axis is called the ''I'' (in-phase) axis, and the ''y'' axis is called the ''Q'' (quadrature) axis. Polar modulation makes use of polar coordinates, ''r'' (amplitude) and ''Θ'' (phase). The quadrature modulator approach to digital radio transmission requires a linear RF power amplifier which creates a design conflict between improving power efficiency or maintaining amplifier linearity. Compromising linearity causes degraded signal quality, usually by adjacent channel degradation, which can be a fundamental factor in limiting network performance and capacity. Additional problems with linear RF power amplifiers, including device parametric restrictions, temperature instability, power control accuracy, wideband noise and prod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clock Pulse
In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits. A clock signal is produced by a clock generator. Although more complex arrangements are used, the most common clock signal is in the form of a square wave with a 50% duty cycle, usually with a fixed, constant frequency. Circuits using the clock signal for synchronization may become active at either the rising edge, falling edge, or, in the case of double data rate, both in the rising and in the falling edges of the clock cycle. Digital circuits Most integrated circuits (ICs) of sufficient complexity use a clock signal in order to synchronize different parts of the circuit, cycling at a rate slower than the worst-case internal propagation delays. In some cases, more than one clock cycle is required to perform a predictable action. As ICs become more ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. The carrier is higher in frequency than the modulation signal. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency-division multiplexing (FDM). For example in cable television which uses FDM, many carrier signals, each modulated with a different television channel, are transported through a sing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
