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A clock generator is an
electronic oscillator An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating ...
that produces a
clock signal 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 si ...
for use in synchronizing a circuit's operation. The signal can range from a simple symmetrical
square wave A square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same duration at minimum and maximum. In an ideal square wave, the transitions b ...
to more complex arrangements. The basic parts that all clock generators share are a resonant circuit and an amplifier. The resonant circuit is usually a
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...
piezo-electric
oscillator Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
, although simpler
tank circuit An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit, is an electric circuit consisting of an inductor, represented by the letter L, and a capacitor, represented by the letter C, connected together. The circuit can ac ...
s and even
RC circuit A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. It may be driven by a voltage or current source and these will produce different responses. A first order RC ...
s may be used. The
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...
circuit usually inverts the signal from the oscillator and feeds a portion back into the oscillator to maintain oscillation. The generator may have additional sections to modify the basic signal. The 8088 for example, used a 2/3
duty cycle A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a form ...
clock, which required the clock generator to incorporate logic to convert the 50/50 duty cycle which is typical of raw oscillators. Other such optional sections include frequency divider or
clock multiplier In computing, the clock multiplier (or CPU multiplier or bus/core ratio) sets the ratio of an internal CPU clock rate to the externally supplied clock. A CPU with a 10x multiplier will thus see 10 internal cycles (produced by PLL-based frequency ...
sections. Programmable clock generators allow the number used in the divider or multiplier to be changed, allowing any of a wide variety of output frequencies to be selected without modifying the hardware. The clock generator in a motherboard is often changed by computer enthusiasts to control the speed of their
CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...
, FSB, GPU and RAM. Typically the programmable clock generator is set by the BIOS at boot time to the selected value; although some systems have dynamic frequency scaling, which frequently re-programs the clock generator.


Timing-signal generators (TSGs)

TSGs are
clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and ...
s that are used throughout service-provider networks, frequently as the building integrated timing supply ( BITS) for a central office. Digital switching systems and some transmission systems (e.g., SONET) depend on reliable, high-quality synchronization (or timing) to prevent impairments. To provide this, most service providers utilize interoffice synchronization distribution networks based on the stratum hierarchy and implement the BITS concept to meet intraoffice synchronization needs. A TSG is clock equipment that accepts input timing reference signals and generates output timing reference signals. The input reference signals can be either DS1 or composite-clock (CC) signals, and the output signals can also be DS1 or CC signals (or both). A TSG is made up of the six components listed below: # An input timing interface that accepts DS1 or CC input signals. # A timing-generation component that creates the timing signals used by the output timing-distribution component. # An output timing distribution component that utilizes the timing signals from the timing-generation component to create multiple DS1 and CC output signals. # A performance-monitoring (PM) component that monitors the timing characteristics of the input signals. # An alarm interface that connects to the central-office (CO) alarm-monitoring system. # An operations interface for local crafts person use and communications with remote operations systems.


See also

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External links


Datasheets of clock generators from Nuvoton / Winbond

Datasheets of clock generators from IDT

Datasheets of clock generators from Realtek

Datasheets of clock generators from Pericom Semiconductor
{{DEFAULTSORT:Clock generator Clock signal Electronic oscillators