Editing Signal generator

{{Short description|Electronic devices that generate electronic signals}}
{{redirect|Tone generator|an electronic musical instrument|Sound module}}
A '''signal generator''' is one of a class of [[Electronics|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 in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices, though it often has artistic uses as well. <ref>{{cite web |title=What is a Signal Generator? |url=https://www.tek.com/learning/signal-generator-tutorial |website=Tektronix}}</ref>

There are many different types of signal generators with different purposes and applications and at varying levels of expense. These types include [[function generator]]s, RF and microwave signal generators, pitch generators, [[arbitrary waveform generator]]s, [[digital pattern generator]]s, and frequency generators. In general, no device is suitable for all possible applications.

A signal generator may be as simple as an oscillator with calibrated  frequency and amplitude. More general-purpose signal generators allow control of all the characteristics of a signal.  Modern general-purpose signal generators will have a microprocessor control and may also permit control from a personal computer. Signal generators may be free-standing self-contained instruments, or may be incorporated into more complex automatic test systems.

==History==
In June 1928, the [[General Radio]] 403 was the first commercial signal generator ever marketed. It supported a frequency range of 500&nbsp;Hz to 1.5&nbsp;MHz.<ref>{{cite web |last1=Burke |first1=Charles |title=The Standard-Signal Method of Measuring Receiver Characteristics |url=https://www.ietlabs.com/pdf/GR_Experimenters/1930/GenRad_Experimenter_March_1930.pdf |publisher=[[General Radio]] |archive-url=https://web.archive.org/web/20181218110326/https://www.ietlabs.com/pdf/GR_Experimenters/1930/GenRad_Experimenter_March_1930.pdf |archive-date=December 18, 2018 |date=March 1930 |quote=Experimenter - Issue Vol. IV, No. 10 |url-status=live}}</ref>  Also, in April 1929, the first commercial frequency standard was marketed by General Radio with a frequency of 50&nbsp;KHz.<ref>{{cite web |last1=Thiessen |first1=Arthur |title=A History of the General Radio Company 1915-1965 |url=http://www.ietlabs.com/pdf/GR_books/AET%20GR%20History%201915%20to%201965.PDF |publisher=[[General Radio]] |archive-url=https://web.archive.org/web/20181218051337/http://www.ietlabs.com/pdf/GR_books/AET%20GR%20History%201915%20to%201965.PDF |archive-date=December 18, 2018 |date=1965 |url-status=live}}</ref>

== General-purpose signal generators ==

=== Function generator ===
[[File:Leader LSG-15 signal generator.jpg|thumb|350px|[[Leader Instruments]] LSG-15 signal generator]]
{{main|Function generator}}

A [[function generator]] is a device which produces simple repetitive [[waveform]]s. Such devices contain an [[electronic oscillator]], a [[Electronic circuit|circuit]] that is capable of creating a repetitive [[waveform]]. (Modern devices may use [[digital signal processing]] to synthesize waveforms, followed by a [[digital-to-analog converter]], or DAC, to produce an analog output.) The most common waveform is a [[sine wave]], but [[sawtooth wave|sawtooth]], step ([[pulse (signal processing)|pulse]]), [[Square wave (waveform)|square]], and [[triangle wave|triangular]] waveform oscillators are commonly available as are [[arbitrary waveform generator]]s (AWGs). If the oscillator operates above the human hearing range (>20&nbsp;[[kHz]]), the generator will often include some sort of [[modulation]] function such as [[amplitude modulation]] (AM), [[frequency modulation]] (FM), or [[phase modulation]] (PM) as well as a second oscillator that provides an [[audio frequency]] modulation waveform.

=== Arbitrary waveform generator ===
{{main|Arbitrary waveform generator}}

An arbitrary waveform generator (AWG or ARB) is a sophisticated signal generator that generates arbitrary waveforms within published limits of [[frequency]] range, accuracy, and output level. Unlike a function generator that produces a small set of specific waveforms, an AWG allows the user to specify a source waveform in a variety of different ways. An AWG is generally more expensive than a function generator and often has less bandwidth. An AWG is used in higher-end design and test applications.

=== RF and microwave signal generators ===
[[Radio frequency|RF (radio frequency)]] and [[microwave]] signal generators are used for testing components, receivers and test systems in a wide variety of applications including cellular communications, [[WiFi]], [[WiMAX]], [[Global Positioning System|GPS]], audio and video broadcasting, satellite communications, [[radar]] and [[electronic warfare]]. RF and microwave signal generators normally have similar features and capabilities, but are differentiated by frequency range. RF signal generators typically range from a few kHz to 6&nbsp;GHz, while microwave signal generators cover a much wider frequency range, from less than 1&nbsp;MHz to at least 20&nbsp;GHz. Some models go as high as 70&nbsp;GHz with a direct coaxial output, and up to hundreds of GHz when used with external waveguide multiplier modules. RF and microwave signal generators can be classified further as analog or vector signal generators.

==== Analog signal generators ====
[[File:E8257D PSG Analog Signal Generator.jpg|right|400px|thumb|An analog RF signal generator]]
Analog signal generators based on a sine-wave oscillator were common before the inception of digital electronics, and are still used. There was a sharp distinction in purpose and design of radio-frequency and audio-frequency signal generators.

;RF
RF signal generators produce [[continuous wave]] radio frequency signals of defined, adjustable,  amplitude and frequency. Many models offer various types of analog modulation, either as standard equipment or as an optional capability to the base unit. This could include [[Amplitude modulation|AM]], [[Frequency modulation|FM]], [[Phase modulation|ΦM (phase modulation)]] and [[pulse modulation]]. A common feature is an [[Attenuator (electronics)|attenuator]] to vary the signal’s output power. Depending on the manufacturer and model, output powers can range from −135 to +30&nbsp;dBm. A wide range of output power is desirable, since different applications require different amounts of signal power. For example, if a signal has to travel through a very long cable out to an antenna, a high output signal may be needed to overcome the losses through the cable and still have sufficient power at the antenna. But when testing receiver sensitivity, a low signal level is required to see how the receiver behaves under low signal-to-noise conditions.

RF signal generators are available as benchtop instruments, rackmount instruments, embeddable modules and in card-level formats. Mobile, field-testing and airborne applications benefit from lighter, battery-operated platforms.  In automated and production testing, web-browser access, which allows multi-source control, and faster frequency switching speeds improve test times and throughput.

RF signal generators are required for servicing and setting up [[radio receiver]]s, and are used for professional RF applications.

RF signal generators are characterized by their frequency bands, power capabilities (−100 to +25&nbsp;dBc), single side band phase noise at various carrier frequencies, spurs and harmonics, frequency and amplitude switching speeds and modulation capabilities.

;AF
Audio-frequency signal generators generate signals in the audio-frequency range and above. An early example was the [[HP200A]] audio oscillator, the first product sold by the [[Hewlett-Packard|Hewlett-Packard Company]] in 1939. Applications include checking frequency response of audio equipment, and many uses in the electronic laboratory.

Equipment [[distortion]] can be measured using a very-low-distortion audio generator as the signal source, with appropriate equipment to measure output distortion harmonic-by-harmonic with a [[Spectrum analyser|wave analyser]], or simply [[total harmonic distortion]]. A distortion of 0.0001% can be achieved by an audio signal generator with a relatively simple circuit.<ref>[http://www.waynekirkwood.com/Images/pdf/Cyril_Bateman/Bateman_Notes_Cap_Sound_1.pdf Capacitor Sounds 1 - Low Distortion (sub 1PPM ) 1 kHz Test Oscillator, C Bateman, Electronics World July 2002, expanded March 2003]. Description, measurements, circuit, and PCB layout</ref>

==== Vector signal generator ====
[[File:E4438C ESG Vector Signal Generator.jpg|right|400px|thumb|A vector signal generator]]
With the advent of digital communications systems, it is no longer possible to adequately test these systems with traditional analog signal generators. This has led to the development of the vector signal generator, which is also known as a digital signal generator. These signal generators are capable of generating digitally-modulated radio signals that may use any of a large number of [[digital modulation]] formats such as [[QAM]], [[QPSK]], [[Frequency-shift keying|FSK]], [[BPSK]], and [[OFDM]]. In addition, since modern commercial digital communication systems are almost all based on well-defined industry standards, many vector signal generators can generate signals based on these standards. Examples include [[GSM]], [[WCDMA|W-CDMA (UMTS)]], [[CDMA2000]], [[Long Term Evolution|LTE]], [[WiFi|Wi-Fi (IEEE 802.11)]], and [[WiMAX|WiMAX (IEEE 802.16)]]. In contrast, military communication systems such as [[JTRS]], which place a great deal of importance on robustness and information security, typically use very proprietary methods. To test these types of communication systems, users will often create their own custom waveforms and download them into the vector signal generator to create the desired test signal.

==== Digital pattern generator ====
{{Main article|Digital pattern generator}}
A logic signal generator or data pattern generator or [[digital pattern generator]] produces logic signals—that is, logical 1s and 0s in the form of conventional voltage levels. The usual voltage standards are [[LVTTL]] and [[LVCMOS]].
It is different from a "pulse/pattern generator", which refers to signal generators able to generate logic pulses with different analog characteristics (such as pulse rise/fall time, high level length, ...).

A digital pattern generator is used as stimulus source for digital integrated circuits and embedded systems - for functional validation and testing.

== Special purpose signal generators ==
[[File:Tone-generator-and-wire-tracker-0a.jpg|thumb|right|A pitch generator and a probe for locating a specific pair of wires amongst many, for example in a [[punch block]].]]

In addition to the above general-purpose devices, there are several classes of signal generators designed for specific applications.

=== Pitch generators and audio generators ===

A pitch generator is a type of signal generator optimized for use in [[sound reproduction|audio]] and [[acoustics]] applications. Pitch generators typically include sine waves over the human hearing range (20 [[Hertz|Hz]] to 20&nbsp;kHz). Sophisticated pitch generators will also include sweep generators (a function which varies the output frequency over a range, in order to make frequency-domain measurements), multipitch generators (which output several pitches simultaneously, and are used to check for [[intermodulation distortion]] and other non-linear effects), and tone bursts (used to measure response to transients). Pitch generators are typically used in conjunction with [[sound level meter]]s, when measuring the acoustics of a room or a sound reproduction system, and/or with oscilloscopes or specialized audio analyzers.

Many pitch generators operate in the [[Digital data|digital]] domain, producing output in various digital audio formats such as [[AES3]], or [[SPDIF]]. Such generators may include special signals to stimulate various digital effects and problems, such as [[Clipping (signal processing)|clipping]], [[jitter]], [[bit error]]s; they also often provide ways to manipulate the [[metadata]] associated with digital audio formats.

The term [[synthesizer]] is used for a device that generates audio signals for music, or that uses slightly more intricate methods.

==== Computer programs ====
[[Computer program]]s can be used to generate arbitrary waveforms on a general-purpose computer and output the waveform via an output interface. Such programs may be provided commercially or be freeware. Simple systems use a standard computer [[sound card]] as output device, limiting the accuracy of the output waveform and limiting frequency to lie within the [[audio-frequency]] band.

=== Video signal generator ===
{{main|Video signal generator}}
A video signal generator is a device which outputs predetermined video and/or television waveforms, and other signals used to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain [[synchronization]] signals appropriate for television, including horizontal and vertical sync pulses (in analog) or sync words (in digital). Generators of ''composite'' video signals (such as [[NTSC]] and [[PAL]]) will also include a [[colorburst]] signal as part of the output. Video signal generators are available for a wide variety of applications and for a wide variety of digital formats; many of these also include audio generation capability (as the audio track is an important part of any video or television program or motion picture).

==See also==
* [[AN/URM-25D signal generator]], 1950s hardware still in use today.
* [[Digital pattern generator]], for generating digital (logic) type of signals
* [[Inductive amplifier]], used to find an individual telephone cable pairs

==References==
<references />

==External links==
{{Commons category|Signal generators}}
* [http://www.bkprecision.com/support/downloads/function-and-arbitrary-waveform-generator-guidebook.html Function Generator & Arbitrary Waveform Generator Guidebook]
* [http://www.radio-electronics.com/info/t_and_m/generators/rf-signal-generator-specs-specifications.php Understanding signal generator specifications]
* [https://www.tek.com/blog/types-of-signal-generators Types of signal generators]
* [https://tonegeneratoronline.net/ Tone signals generator]

{{Electrical and electronic measuring equipment}}

{{Authority control}}

[[Category:Laboratory equipment]]
[[Category:Electronic test equipment]]