A comb generator is a
signal generator
A signal generator is one of a class of electronic devices that generates electrical signals with set properties of amplitude, frequency, and wave shape. These generated signals are used as a stimulus for electronic measurements, typically used i ...
that produces multiple
harmonics of its input signal. The appearance of the output at the
spectrum analyzer
A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal that most co ...
screen, resembling teeth of a
comb
A comb is a tool consisting of a shaft that holds a row of teeth for pulling through the hair to clean, untangle, or style it. Combs have been used since prehistoric times, having been discovered in very refined forms from settlements dating ba ...
, gave the device its name.
Comb generators find wide range of uses in
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
technology. E.g., synchronous signals in wide frequency bandwidth can be produced by a comb generator. The most common use is in broadband
frequency synthesizer
A frequency synthesizer is an electronic circuit that generates a range of frequencies from a single reference frequency. Frequency synthesizers are used in many modern devices such as radio receivers, televisions, mobile telephones, radiotelephon ...
s, where the high frequency signals act as stable references correlated to the lower energy references; the outputs can be used directly, or to synchronize
phase-locked loop
A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. There are several different types; the simplest is an electronic circuit consisting of a ...
oscillators. It may be also used to generate a complete set of substitution channels for testing, each of which carries the same baseband audio and video signal.
Comb generators are also used in
RFI testing of
consumer electronics
Consumer electronics or home electronics are electronic ( analog or digital) equipment intended for everyday use, typically in private homes. Consumer electronics include devices used for entertainment, communications and recreation. Usuall ...
, where their output is used as a simulated
RF emissions, as it is a stable broadband noise source with repeatable output. It is also used during compliance testing to various government requirements for products such as medical devices (FDA), military electronics (
MIL-STD-461
MIL-STD-461 is a United States Military Standard that describes how to test equipment for electromagnetic compatibility
Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their electr ...
), commercial avionics (Federal Aviation Administration), digital electronics (Federal Communications Commission), in the USA.
An optical comb generator can be used as generators of
terahertz radiation
Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency
(THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of fre ...
. Internally, it is a
resonant electro-optic modulator, with the capability of generating hundreds of
sideband
In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands c ...
s with total span of at least 3 terahertz (limited by the
optical dispersion
In optics, and by analogy other branches of physics dealing with wave propagation, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency; sometimes the term chromatic dispersion is used for specificity to o ...
of the
lithium niobate
Lithium niobate () is a non-naturally-occurring salt consisting of niobium, lithium, and oxygen. Its single crystals are an important material for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linea ...
crystal) and frequency spacing of 17 GHz. Other construction can be based on erbium-doped
fiber laser or
Ti-sapphire laser
Ti:sapphire lasers (also known as Ti:Al2O3 lasers, titanium-sapphire lasers, or Ti:sapphs) are tunable lasers which emit red and infrared, near-infrared light in the range from 650 to 1100 nanometers. These lasers are mainly used in scientific res ...
often in combination with
carrier envelope offset control.
See also
*
Comb filter
In signal processing, a comb filter is a filter implemented by adding a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly space ...
*
Frequency comb In optics, a frequency comb is a laser source whose spectrum consists of a series of discrete, equally spaced frequency lines. Frequency combs can be generated by a number of mechanisms, including periodic modulation (in amplitude and/or phase) of a ...
References
{{Reflist
External links
Yet another comb generatorCom-Power Corporation
Laboratory equipment
Electronic test equipment
Signal processing
Terahertz technology