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Encyclopedia > Clock signal

In electronics and especially synchronous digital circuits, a clock signal is a signal used to coordinate the actions of two or more circuits. A clock signal oscillates between a high and a low state, normally with a 50% duty cycle, and is usually in the form of a square wave. Circuits using the clock signal for synchronization may become active at either the rising edge, falling edge, or both edges of the clock cycle; for example, DDR SDRAM is activated by both edges. This article is about the engineering discipline. ... A synchronous circuit is a digital circuit in which the parts are synchronized by a clock signal. ... Digital circuits are electric circuits based on a number of discrete voltage levels. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes. ... Oscillation is the variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. ... In telecommunication and electronics, the term duty cycle has the following meanings: The duty cycle D is defined as the ratio between the pulse duration () and the period (T) of a rectangular waveform In a periodic phenomenon, the ratio of the duration of the phenomenon in a given period to... A square wave is a kind of basic waveform. ... DDR SDRAM or double-data-rate synchronous dynamic random access memory is a type of memory integrated circuit used in computers. ...

## Contents

Most integrated circuits (ICs) of sufficient complexity utilize a clock signal in order to synchronize different parts of the circuit and to account for propagation delays. 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, the central component of modern computers, which relies on a clock from a crystal oscillator. Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... In computer science, the propogation delay is the amount of time starting from when the input to a logic gate becomes stable and valid to the time that the output of that logic gate is stable and valid. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... 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. ...

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 IMP-16 family, a multi-phase 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. Most modern microprocessors and microcontrollers use a single-phase clock, however. Categories: Electronics companies of the United States | Companies based in California | Corporation stubs ... This article is about a portion of a periodic process. ... It has been suggested that this article or section be merged with embedded microprocessor. ...

Many modern microcomputers utilize a "clock multiplier" which multiplies a lower frequency external clock to the appropriate clock rate 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). The Commodore 64 was one of the most popular microcomputers of its era, and is the best selling model of home computer of all time. ... The clock rate is the fundamental rate in cycles per second (measured in hertz) at which a computer performs its most basic operations such as adding two numbers or transferring a value from one processor register to another. ... Energy Input: The energy placed into a reaction. ...

## Other circuits

In CMOS circuits, gate capacitances are charged and uncharged continually. A capacitor does not dissipate energy, but energy is wasted in the driving transistors. Inductors 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. An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... CMOS Transmission Gate A transmission gate is an electronic element. ...

## Distribution

The clock signal must be propogated 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). In a synchronous digital system, the clock signal is used to define a time reference for the movement of data within that system. ... The first ten levels of an H tree The H tree (so called because its first two steps resemble the letter H) is a family of fractal sets whose Hausdorff dimension is equal to 2. ... Results from FactBites:

 Clock - Wikipedia, the free encyclopedia (1424 words) Clocks are in homes and offices; smaller ones (watches) are carried; larger ones are in public places, e.g. A clock is a recurrent, periodic process and a counter. A clock face is the part of an analog clock that tells time through the use of a fixed numbered dial or dials and moving hand or hands.
 Clock signal - Wikipedia, the free encyclopedia (302 words) A clock signal oscillates between a high and a low state, normally with a 50% duty cycle, and is usually a square wave. The circuits using the clock signal for synchronization may become active at either the rising or falling edge, or both (see for example DDR SDRAM), of the clock signal. Such sine wave clocks are often differential signals, because this type of signal has twice the slew rate, and therefore half the timing uncertainty, of a single-ended signal with the same voltage range.
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