In electronics and especially synchronous digital circuits, a clock signal is a signal used to coordinate the actions of two or more circuits. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical A synchronous circuit is a Digital circuit in which the parts are synchronized by a Clock signal. Digital electronics are Electronics systems that use Digital signals Digital electronics are representations of Boolean algebra also see In Telecommunication, signalling (UK spelling or signaling (US spelling has the following meanings The use of signals for controlling communications An electronic circuit is a closed path formed by the interconnection of Electronic components through which an Electric current can flow 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. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states In Telecommunications and Electronics, the term duty cycle is used to describe the fraction of time that a system is in an "active" state A square wave is a kind of Non-sinusoidal waveform, most typically encountered in Electronics and Signal processing. 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. DDR SDRAM ( double data rate synchronous dynamic random access memory) is a class of memory Integrated circuit used in Computers It achieves nearly twice
Contents |
Digital circuits
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. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Networking Propagation delay is defined as how long it takes for a certain amount of bytes to transfered over a medium 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. A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated A crystal oscillator is an Electronic circuit that uses the mechanical Resonance of a vibrating Crystal of piezoelectric material to create an
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. National Semiconductor ( is a Semiconductor manufacturer specializing in analog devices and subsystems headquartered in Santa Clara, California, 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 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. A microcontroller (also MCU or µC is a functional Computer system-on-a- chip.
Many modern microcomputers utilize a "clock multiplier" which multiplies a lower frequency external clock to the appropriate clock rate of the microprocessor. microcomputer is a Computer with a Microprocessor as its Central processing unit. The clock multiplier (or CPU multiplier or bus/core ratio) is the ratio of the internal CPU Clock rate to the frequency of its external address/data bus 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 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 (such as a Computer) and the outside
Other circuits
Some sensitive mixed-signal circuits, such as precision analog-to-digital converters, use sine waves rather than square waves as their clock signals, because square waves contain high-frequency harmonics that can interfere with the analog circuitry and cause noise. A mixed-signal Integrated circuit combines Analog circuits, used for analog signal processing with Digital signal processing (DSP circuits on a single An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic integrated circuit which converts continuous signals to In Acoustics and Telecommunication, the harmonic of a Wave is a component Frequency of the signal that is an Integer In Science, and especially in Physics and Telecommunication, noise is fluctuations in and the addition of external factors to the stream of target 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. Differential signaling is a method of transmitting Information electrically by means of two complementary Signals sent on two separate wires In Electronics, the slew rate represents the maximum rate of change of a signal at any point in a circuit Single-ended signalling is the simplest commonly used method of transmitting Electrical signals over Wires One wire carries a varying Voltage that represents 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. Inductors can be used to store this energy and reduce the energy loss, but they tend to be quite large. An inductor is a passive electrical component designed to provide Inductance in a circuit Alternatively, using a sine wave clock, CMOS transmission gates and energy-saving techniques, the power requirements can be reduced. A transmission gate is an electronic element It is a good non-mechanical Relay, built with CMOS technology
Distribution
The clock signal must be propagated with a clock distribution network. In a synchronous digital system, the Clock signal is used to define a time reference for the movement of data within that system This is often done with a recursive 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 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
- Programmable Interval Timer
- Synchronous circuit
- Clock rate
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic