In electronics Electronics is the branch of science and technology which makes use of the controlled motion of electrons through different media and vacuum. The ability to control electron flow is usually applied to information handling or device control. Electronics is distinct from electrical science and technology, which deals with the generation, and especially synchronous In an ideal synchronous circuit, every change in the logical levels of its storage components is simultaneous. These transitions follow the level change of a special signal called the clock. Ideally, the input to each storage element has reached its final value before the next clock occurs, so the behaviour of the whole circuit can be predicted digital circuits Digital electronics are systems that represent signals as discrete levels, rather than as a continuous range. In most cases the number of states is two, and these states are represented by two voltage levels: one near to zero volts and one at a higher level depending on the supply voltage in use. These two levels are often represented as "Low&, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome A metronome is any device that produces regular, metrical ticks . These ticks represent a fixed, regular aural pulse; some metronomes also include synchronized visual motion (e.g. pendulum-swing). The metronome dates back to the early 19th century. Though the metronome was conceived as a tool for music, some musicians consider it to be a highly to coordinate actions of circuits An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electrical current can flow. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified,. Although the word signal has a number of other meanings, the term is here used for "transmitted energy that can carry information".
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 A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels with a 50% duty cycle In telecommunications and electronics, the duty cycle is the fraction of time that a system is in an "active" state. In particular, it is used in the following contexts:, 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.
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Digital circuits
Most integrated circuits In electronics, an integrated circuit is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material. Integrated circuits are used in almost all electronic equipment in use today and have revolutionized the (ICs) of sufficient complexity use a clock signal in order to synchronize different parts of the circuit and to account for propagation delays Propagation delay is a technical term that can have a different meaning depending on the context. It can relate to networking, electronics or physics. In general it is the length of time taken for the quantity of interest to reach its destination. As ICs become more complex, the problem of supplying accurate and synchronized clocks to all the circuits becomes increasingly difficult. The preeminent example of such complex chips is the microprocessor A microprocessor incorporates most or all of the functions of a computer's central processing unit on a single integrated circuit (IC, or microchip). The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic in 4-bit words. Other embedded uses of 4-bit and 8-bit, the central component of modern computers, which relies on a clock from a crystal oscillator A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time , to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for. The only exceptions are asynchronous circuits An asynchronous circuit is a circuit in which the parts are largely autonomous. They are not governed by a clock circuit or global clock signal, but instead need only wait for the signals that indicate completion of instructions and operations. These signals are specified by simple data transfer protocols. This digital logic design is contrasted such as asynchronous CPUs An asynchronous circuit is a circuit in which the parts are largely autonomous. They are not governed by a clock circuit or global clock signal, but instead need only wait for the signals that indicate completion of instructions and operations. These signals are specified by simple data transfer protocols. This digital logic design is contrasted.
A clock signal might also be gated, that is, combined with a controlling signal that enables or disables the clock signal for a certain part of a circuit. This technique is often used to save power by effectively shutting down portions of a digital circuit when they are not in use.
In some early microprocessors such as the National Semiconductor National Semiconductor is a semiconductor manufacturer, specializing in analog devices and subsystems, headquartered in Santa Clara, California, USA. The products of National Semiconductor include power management circuits, display drivers, audio and operational amplifiers, communication interface products and data conversion solutions. National's IMP-16 family, a multi-phase The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0. Phase is a frequency domain or Fourier transform domain concept, and as such, can be readily understood in terms of simple harmonic motion. The same concept applies to wave motion, clock was used. In the case of the IMP-16, the clock had four phases, each 90 degrees apart, in order to synchronize the operations of the processor core and its peripherals. The MOS Technology 6502 The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. When it was introduced, it was the least expensive full-featured microprocessor on the market by a considerable margin, costing less than one-sixth the price of competing designs from larger companies such as Motorola had 2 clock phases. Some ICs use four-phase logic. Most modern microprocessors and microcontrollers A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to use a single-phase clock, however.
Many modern microcomputers A microcomputer is a computer with a microprocessor as its central processing unit. They are physically small compared to mainframe and minicomputers. Many microcomputers are also personal computers (in the generic sense) use a "clock multiplier" which multiplies a lower frequency external clock to the appropriate clock rate The clock rate is the rate in cycles per second for the frequency of the clock in any synchronous circuit (such as a CPU). For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry (AD Converter) into a corresponding of the microprocessor. This allows the CPU to operate at a much higher frequency than the rest of the computer, which affords performance gains in situations where the CPU does not need to wait on an external factor (like memory or input/output In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it. The term can also be used as part of an action; to &).
Dynamic frequency change
The vast majority of digital devices do not require a clock at a fixed, constant frequency. As long as the minimum and maximum clock times are respected, the time between clock edges can vary widely from one edge to the next. Such digital devices work just as well with a clock generator that dynamically changes its frequency, such as spread-spectrum clock generation Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference and, PowerNow! PowerNow! is speed throttling and power saving technology of AMD's processors used in laptops. The CPU's clock speed and VCore are automatically decreased when the computer is under low load or idle, to save battery power, reduce heat and noise. The lifetime of the CPU is also extended because of reduced electromigration, which varies, Cool'n'Quiet, SpeedStep SpeedStep is a trademark for a series of dynamic frequency scaling technologies built into some Intel microprocessors that allow the clock speed of the processor to be dynamically changed by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw and heat, etc. Devices that use static logic do not even have a maximum clock time; such devices can be slowed down and paused indefinitely, then resumed at full clock speed at any later time.
Other circuits
Some sensitive mixed-signal circuits A mixed-signal integrated circuit is any integrated circuit that has both analog circuits and digital circuits on a single semiconductor die, such as precision analog-to-digital converters An analog-to-digital converter is a device which converts continuous signals to discrete digital numbers. The reverse operation is performed by a digital-to-analog converter (DAC), use sine waves The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields. Its most basic form as a function of time is: rather than square waves as their clock signals, because square waves contain high-frequency harmonics A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental frequency, therefore the sum of harmonics is also periodic that can interfere with the analog circuitry and cause noise Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects. Thermal noise and shot noise are inherent to all devices, while other types depend mostly on manufacturing quality and semiconductor. Such sine wave clocks are often differential signals, because this type of signal has twice the slew rate In electronics, the slew rate represents the maximum rate of change of a signal at any point in a circuit. Limitations in slew rate capability can give rise to non linear effects in electronic amplifiers. For a sinusoidal waveform not to be subject to slew rate limitation, the slew rate capability at all points in an amplifier must satisfy the, and therefore half the timing uncertainty, of a single-ended signal with the same voltage range. Differential signals radiate less strongly than a single line. Alternatively, a single line shielded by power and ground lines can be used.
In CMOS circuits, gate capacitances are charged and uncharged continually. A capacitor does not dissipate energy, but energy is wasted in the driving transistors. In reversible computing, inductors An inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries. Typically an inductor is a conducting wire shaped as a coil, the loops helping to create a strong can be used to store this energy and reduce the energy loss, but they tend to be quite large. Alternatively, using a sine wave clock, CMOS transmission gates and energy-saving techniques, the power requirements can be reduced.[citation needed]
Distribution
The most effective way to get the clock signal to every part of a chip that needs it, with the lowest skew, is a metal grid. In a large microprocessor, the power used to drive the clock signal can be over 30% of the total power used by the entire chip.[1] The clock signal must be propagated with a clock distribution network. This is often done with a recursive H tree. The whole structure with the gates at the ends and all amplifiers in between have to be loaded and unloaded every cycle. To save energy, unused parts of the tree may be temporarily cut off (clock gating).
See also
- Self-clocking signal
- Four-phase logic
- Jitter Jitter in technical terms is the deviation in or displacement of some aspect of the pulses in a high-frequency digital signal. As the name suggests, jitter can be thought of as shaky pulses. The deviation can be in terms of amplitude, phase timing, or the width of the signal pulse. Another definition is that it is "the period frequency
- Programmable Interval Timer
- Synchronous circuit In an ideal synchronous circuit, every change in the logical levels of its storage components is simultaneous. These transitions follow the level change of a special signal called the clock. Ideally, the input to each storage element has reached its final value before the next clock occurs, so the behaviour of the whole circuit can be predicted
- Clock rate The clock rate is the rate in cycles per second for the frequency of the clock in any synchronous circuit (such as a CPU). For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry (AD Converter) into a corresponding
References
- ^ "Intel's Atom Architecture: The Journey Begins" by Anand Lal Shimpi, 2008
Categories: Clock signal
