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A frequency-locked loop is an example of a control system using negative feedback. Frequency-lock loops are used in radio, telecommunications, computers and other electronic applications to generate stable frequencies, or to recover a signal from a noisy communication channel.
Injection pulling and injection locking can be observed in numerous physical systems where pairs of oscillators are coupled together. Perhaps the first to document these effects was Christiaan Huygens, the inventor of the pendulum clock, who was surprised to note that two pendulum clocks which normally would keep slightly different time nonetheless became perfectly synchronized when hung from ...
A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is fixed relative to the phase of an input signal. Keeping the input and output phase in lockstep also implies keeping the input and output frequencies the same, thus a phase-locked loop can also track an input frequency.
A frequency synthesizer may use the techniques of frequency multiplication, frequency division, direct digital synthesis, frequency mixing, and phase-locked loops to generate its frequencies. The stability and accuracy of the frequency synthesizer's output are related to the stability and accuracy of its reference frequency input.
Floyd M. Gardner introduced "a lock-in range concept" for PLLs and posed the problem on its formalization (known as the Gardner problem on the lock-in range [5] [6]).In the 1st edition of his book he introduced a lock-in frequency concept for the PLL in the following way: [1]: 40 "If, for some reason, the frequency difference between input and VCO is less than the loop bandwidth, the loop will ...
Direct digital synthesis (DDS) is a method employed by frequency synthesizers used for creating arbitrary waveforms from a single, fixed-frequency reference clock. DDS is used in applications such as signal generation , local oscillators in communication systems, function generators , mixers, modulators , [ 1 ] sound synthesizers and as part of ...
Schematic of PDH servo loop to lock the frequency of a laser (top left) to a Fabry–Perot cavity (top right). Light from the laser is sent through a phase-modulator and is then directed upon the cavity.
The loop may not lock within one beat note, but the VCO frequency will be slowly tuned toward the reference frequency (acquisition process). This effect is also called a transient stability. The pull-in range is used to name such frequency deviations that make the acquisition process possible (see, for example, explanations in Gardner (1966 , p.