A signal generator is one of a class of
electronic
Electronic may refer to:
*Electronics, the science of how to control electric energy in semiconductor
* ''Electronics'' (magazine), a defunct American trade journal
*Electronic storage, the storage of data using an electronic device
*Electronic co ...
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.
There are many different types of signal generators with different purposes and applications and at varying levels of expense. These types include
function generator
In electrical engineering, a function generator is usually a piece of electronic test equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced b ...
s, RF and microwave signal generators, pitch generators,
arbitrary waveform generator
An arbitrary waveform generator (AWG) is a piece of electronic test equipment used to generate electrical waveforms. These waveforms can be either repetitive or single-shot (once only) in which case some kind of triggering source is required (i ...
s,
digital pattern generator
A digital pattern generator is a piece of electronic test equipment or software used to generate digital electronic stimuli. Digital electronics stimuli are a specific kind of electrical waveform varying between two conventional voltages that corr ...
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
General Radio Company (later, GenRad) was a broad-line manufacturer of electronic test equipment in Massachusetts, U.S. from 1915 to 2001.
History
On June 14, 1915, Melville Eastham and a small group of investors started General Radio Company ...
403 was the first commercial signal generator ever marketed. It supported a frequency range of 500 Hz to 1.5 MHz. Also, in April 1929, the first commercial frequency standard was marketed by General Radio with a frequency of 50 KHz.
General-purpose signal generators
Function generator
![Leader LSG-15 signal generator](https://upload.wikimedia.org/wikipedia/commons/e/ed/Leader_LSG-15_signal_generator.jpg)
A
function generator
In electrical engineering, a function generator is usually a piece of electronic test equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced b ...
is a device which produces simple repetitive
waveform
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electronic ...
s. Such devices contain an
electronic oscillator
An electronic oscillator is an electronic circuit that produces a periodic, oscillation, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillation, Oscillators convert direct current (DC) from a power supp ...
, a
circuit that is capable of creating a repetitive
waveform
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electronic ...
. (Modern devices may use
digital signal processing
Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...
to synthesize waveforms, followed by a
digital-to-analog converter
In electronics, a digital-to-analog converter (DAC, D/A, D2A, or D-to-A) is a system that converts a digital signal into an analog signal. An analog-to-digital converter (ADC) performs the reverse function.
There are several DAC architec ...
, or DAC, to produce an analog output.) The most common waveform is a
sine wave
A sine wave, sinusoidal wave, or just sinusoid is a curve, mathematical curve defined in terms of the ''sine'' trigonometric function, of which it is the graph of a function, graph. It is a type of continuous wave and also a Smoothness, smooth p ...
, but
sawtooth, step (
pulse
In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the nec ...
),
square
In Euclidean geometry, a square is a regular quadrilateral, which means that it has four equal sides and four equal angles (90-degree angles, π/2 radian angles, or right angles). It can also be defined as a rectangle with two equal-length adj ...
, and
triangular
A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC.
In Euclidean geometry, any three points, when non- collinea ...
waveform oscillators are commonly available as are
arbitrary waveform generator
An arbitrary waveform generator (AWG) is a piece of electronic test equipment used to generate electrical waveforms. These waveforms can be either repetitive or single-shot (once only) in which case some kind of triggering source is required (i ...
s (AWGs). If the oscillator operates above the human hearing range (>20
kHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...
), the generator will often include some sort of
modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
function such as
amplitude modulation
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to ...
(AM),
frequency modulation
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and Run-length limited#FM: .280. ...
(FM), or
phase modulation
Phase modulation (PM) is a modulation pattern for conditioning communication signals for transmission. It encodes a message signal as variations in the instantaneous phase of a carrier wave. Phase modulation is one of the two principal forms ...
(PM) as well as a second oscillator that provides an
audio frequency
An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch.
The generally accepted ...
modulation waveform.
Arbitrary waveform generator
An arbitrary waveform generator (AWG or ARB) is a sophisticated signal generator that generates arbitrary waveforms within published limits of
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
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
RF (radio frequency) and
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 ran ...
signal generators are used for testing components, receivers and test systems in a wide variety of applications including cellular communications,
WiFi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves ...
,
WiMAX
Worldwide Interoperability for Microwave Access (WiMAX) is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide physical layer (PHY) and media access control (MAC) options.
The WiMAX ...
,
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
, audio and video broadcasting, satellite communications,
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
and
electronic warfare
Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponen ...
. 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 GHz, while microwave signal generators cover a much wider frequency range, from less than 1 MHz to at least 20 GHz. Some models go as high as 70 GHz with a direct coaxial output, and up to hundreds of GHz when used with external waveguide source modules. RF and microwave signal generators can be classified further as analog or vector signal generators.
Analog signal generators
![E8257D PSG Analog Signal Generator](https://upload.wikimedia.org/wikipedia/commons/b/be/E8257D_PSG_Analog_Signal_Generator.jpg)
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
A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particle ...
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
AM,
FM,
ΦM (phase modulation) and
pulse modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
. A common feature is an
attenuator to vary the signal’s output power. Depending on the manufacturer and model, output powers can range from −135 to +30 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
In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. Th ...
s, and are used for professional RF applications.
RF signal generators are characterized by their frequency bands, power capabilities (−100 to +25 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
The HP 200A was the first product made by Hewlett-Packard and was manufactured in David Packard's garage in Palo Alto, California.
It was a low-distortion audio oscillator used for testing sound equipment. It used the Wien bridge oscillator cir ...
audio oscillator, the first product sold by the
Hewlett-Packard Company
The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
in 1939. Applications include checking frequency response of audio equipment, and many uses in the electronic laboratory.
Equipment
distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...
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
wave analyser, or simply
total harmonic distortion
The total harmonic distortion (THD or THDi) is a measurement of the harmonic distortion present in a signal and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. Distortion facto ...
. A distortion of 0.0001% can be achieved by an audio signal generator with a relatively simple circuit.
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
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
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
formats such as QAM
Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signal ...
, QPSK
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a ...
, FSK FSK may refer to:
* FSK (band), a German band
* Federal Counterintelligence Service, (Russian ') of Russia
* Fiskerton railway station, in England
* Forskolin, a diterpene
* Forsvarets Spesialkommando, a Norwegian special forces unit
* Fort Scott M ...
, BPSK
Phase-shift keying (PSK) is a digital modulation process which conveys Data (computing), data by changing (modulating) the Phase (waves), phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying ...
, and OFDM
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission and a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital commun ...
. 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
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
, W-CDMA (UMTS), CDMA2000
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible ...
, LTE, Wi-Fi (IEEE 802.11), and WiMAX (IEEE 802.16). In contrast, military communication systems such as JTRS
The Joint Tactical Radio System (JTRS) aimed to replace existing radios in the American military with a single set of software-defined radios that could have new frequencies and modes (“waveforms”) added via upload, instead of requiring mul ...
, 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
A logic signal generator or data pattern generator or digital pattern generator
A digital pattern generator is a piece of electronic test equipment or software used to generate digital electronic stimuli. Digital electronics stimuli are a specific kind of electrical waveform varying between two conventional voltages that corr ...
produces logic signals—that is, logical 1s and 0s in the form of conventional voltage levels. The usual voltage standards are LVTTL and LVCMOS Low voltage complementary metal oxide semiconductor (LVCMOS) is a low voltage class of CMOS technology digital integrated circuits.
Overview
To obtain better performance and lower costs, semiconductor manufacturers reduce the device geometries of i ...
.
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
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 audio
Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to:
Sound
*Audio signal, an electrical representation of sound
*Audio frequency, a frequency in the audio spectrum
*Digital audio, representation of sound ...
and acoustics
Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician ...
applications. Pitch generators typically include sine waves over the human hearing range (20 Hz to 20 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
Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency com ...
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
A sound level meter (also called sound pressure level meter (SPL)) is used for acoustic measurements. It is commonly a hand-held instrument with a microphone. The best type of microphone for sound level meters is the condenser microphone, whic ...
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
Digital usually refers to something using discrete digits, often binary digits.
Technology and computing Hardware
*Digital electronics, electronic circuits which operate using digital signals
**Digital camera, which captures and stores digital i ...
domain, producing output in various digital audio formats such as AES3
AES3 is a standard for the exchange of digital audio signals between professional audio devices. An AES3 signal can carry two channels of pulse-code-modulated digital audio over several transmission media including balanced lines, unbalanced l ...
, or SPDIF
S/PDIF (Sony/Philips Digital Interface) is a type of digital audio interface used in consumer audio equipment to output audio over relatively short distances. The signal is transmitted over either a coaxial cable (using RCA or BNC connectors) ...
. Such generators may include special signals to stimulate various digital effects and problems, such as clipping
Clipping may refer to:
Words
* Clipping (morphology), the formation of a new word by shortening it, e.g. "ad" from "advertisement"
* Clipping (phonetics), shortening the articulation of a speech sound, usually a vowel
* Clipping (publications) ...
, jitter
In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a significa ...
, bit error
In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.
The bit error rate (BER) i ...
s; they also often provide ways to manipulate the metadata
Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive metadata – the descriptive ...
associated with digital audio formats.
The term synthesizer
A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis and ...
is used for a device that generates audio signals for music, or that uses slightly more intricate methods.
Computer programs
Computer program
A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components.
A 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
A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external audio i ...
as output device, limiting the accuracy of the output waveform and limiting frequency to lie within the audio-frequency
An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch.
The generally accepted ...
band.
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
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
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
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
and PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
) will also include a colorburst
Colorburst is an analog video, composite video signal generated by a video-signal generator used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the back porc ...
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
A digital pattern generator is a piece of electronic test equipment or software used to generate digital electronic stimuli. Digital electronics stimuli are a specific kind of electrical waveform varying between two conventional voltages that corr ...
, for generating digital (logic) type of signals
* Inductive amplifier, used to find an individual telephone cable pairs
References
External links
Function Generator & Arbitrary Waveform Generator Guidebook
Understanding signal generator specifications
Types of signal generators
{{Authority control
Laboratory equipment
Electronic test equipment