Function Generator vs. Arbitrary Waveform Generator: What’s the Difference?
Signals play an important role in electronics testing, research, development, troubleshooting and laboratory work. Signal-generation equipment provides test personnel the ability to create controlled electrical signals to stimulate circuits and devices.
Two commonly confused signal-generation devices are a function generator and an arbitrary waveform generator. These devices certainly have some similarities, but their inherent features and applications greatly differ.
Knowledge of each of these differences allows an engineer or technician the opportunity to select the most appropriate signal-generation device for the particular application.
A function generator can provide a selection of standard waveforms such as sine, square, triangle, and ramp signals. Waveforms generated by arbitrary waveform generators can be of any shape and are user defined.
Other factors such as the frequency range, modulation, features, sample rate, memory, and the specific application have to be taken into account when choosing the appropriate signal-generation device.
What Is a Function Generator?
A function generator is an instrument that is used to produce various electrical waveforms commonly found in electronic circuits.
Depending on the model, function generators can provide signals such as:
- Sine waves
- Square waves
- Triangle waves
- Ramp or Sawtooth waves
- Pulses
- Other standard and/or user-defined signals.
These generators are useful to an engineer when a predictable signal is needed to check how a circuit or device responds.
A sine wave of a particular frequency and amplitude can be applied to an amplifier by an engineer in order to troubleshoot. The output of the amplifier can then be measured by an oscilloscope.
An engineer can also use a square wave to test digital circuits, as well as evaluate how a circuit responds to quickly changing voltage levels.
Finally, the standardness of basic waveforms makes function generators extremely useful in a laboratory, educational, repair and development settings.
What Is an Arbitrary Waveform Generator?
An arbitrary waveform generator is more flexible than a traditional function generator. This is because a traditional function generator has limitations to waveform shapes. An arbitrary waveform generator gives the user more flexibility to shape the waveform based on pre-defined voltages, or with a mathematical function.
Also, a function generator produces basic waveforms such as a sine wave. An arbitrary waveform generator can produce an irregular waveform that better resembles the shape of the signal being tested.
An engineer may need to reproduce a complex waveform that resembles a signal captured from a real-world device, or create a waveform with a pattern that is too complex to be reproduced with standard functions.
Depending on the instrument, users can create waveforms with a variety of features using built in software, external software, mathematical functions, waveform editors, imported data, or a combination.
Function Generator vs. Arbitrary Waveform Generator
A function generator can produce basic waveforms that are well-suited for many applications. An arbitrary waveform generator can produce complex waveforms and is well-suited for applications requiring a high degree of flexibility and pattern customization.
Function Generator
Choosing a function generator may be a good idea when you need:
- Basic waveforms
- Simple signal generation
- Rough frequency and amplitude control
- Periodic circuit testing
- Laboratory work
- General troubleshooting
Arbitrary Waveform Generator
Choosing an arbitrary waveform generator may be a good idea when you need:
- The generation of more advanced and varied waveforms
- The reproduction of more advanced and varied signal generation
- Signal modulation
- More advanced signal testing
Neither instrument automatically takes precedence over the other. The decision is dependent on what exactly is required of the instrument.
When Is a Function Generator Appropriate?
A function generator is often appropriate when the required signal is rather basic.
Testing an audio amplifier may require the application of a sine wave at different frequencies. In this case, a function generator is the more appropriate choice.
A function generator may also be appropriate when a square wave is needed to test a digital circuit. A function generator may be able to provide the signal needed for the test.
Routine laboratory tasks may benefit from this simplicity.
When Is an Arbitrary Waveform Generator Appropriate?
An arbitrary waveform generator may be appropriate when the required signal is rather complex.
Imagine an engineer attempts to reproduce a signal captured from a real-world electronic system.
A simple sine or square wave may not accurately represent the signal. The engineer could be required to re-create a signal with time varying amplitude or frequency, or other properties of the signal.
An arbitrary waveform generator would be beneficial in this scenario.
In addition, an arbitrary waveform generator would be helpful in generating complex waveforms for testing devices and instrumentation in a laboratory environment.
It is useful in industry and the military in fields such as research and development, communication systems, automated vehicle control systems, aerospace and other control systems, and other high-tech industries.
Key Specifications to Compare
When selecting a signal-generation instrument, it is important to look beyond the instrument category.
Two instruments in the same instrument category may be significantly different.
Some of the specifications listed below may be important.
Waveform Fidelity
Waveform fidelity is how faithfully a signal is reproduced. In a typical function generator, the reproduced waveform is limited to a few basic waveforms. Other more complex waveforms may be required for other applications.
Frequency Range
The frequency range is important depending upon the application. For example, a radio frequency system would require a generator that has higher performance than a system that operates at a few hertz.
Peak Output Amplitude
The required amplitude depends on the device being tested and the configuration.
While some instruments may have controls to limit the amplitude, other instruments may not offer that control. This may be important for some applications.
A custom waveform generator may be a better choice if custom waveforms are required.
Check the types of waveforms and the level of customization provided before purchase.
Sample Rate
For arbitrary waveforms, sample rate plays an important role.
Depending on the application and other characteristics of the instrument, a higher sample rate may allow the instrument to reproduce a given waveform with more fidelity.
Memory Depth
For arbitrary waveform applications, memory depth plays an important role in how much waveform information is stored and reproduced.
For example, memory depth may play an important role in storing and reproducing an arbitrary long and/or complex waveform.
Modulation
Some applications may require amplitude, frequency, phase or other types of modulation.
In such cases, the signal generator may require modulation of one of the above types to meet the test requirement.
What Is a Signal Generator?
The term signal generator is broadly used for equipment that is used to create controlled electrical signals.
Depending on the instrument, the capability may be limited to create standard waveforms or it may allow for generating complex waveforms and providing modulation.
Because the terminology may vary between manufacturers, it is always prudent to review the actual specifications.
For RF applications, an RF signal generator may be required to create controlled electrical signals over the RF spectrum to test RF components and systems.
For additional technical background, you can reference manufacturer resources such as Tektronix signal generator resources and Keysight's signal generator guide.
Function Generators and RF Signal Generators Are Not Always the Same
Although both instruments are signal generators, their applications may differ. A general-purpose function generator may be appropriate for creating signals for simple or low frequency electronics tests.
RF signal generators create radio frequency signals for various applications.
For example, an RF testing environment may require control of frequency, modulation, purity, and/or level of the signal.
Thus, an engineer should examine the frequency requirements of an application and choose an instrument based upon those requirements.
Selecting an instrument that is merely described as a “signal generator” may not provide sufficient information to assess its appropriateness.
For additional technical reference, Tektronix's signal generator overview explains the differences between function generators, arbitrary waveform generators, and RF signal generators.
Buying Used Signal Generators
For a laboratory or business concerned with controlling their equipment budget, purchasing used signal generators may be an option to obtain professional equipment.
Used equipment, however, needs to be analyzed carefully.
First, the model and specifications need to be confirmed.
Then the physical condition of the equipment needs to be evaluated.
Look for:
- Buttons
- Knobs
- Connectors
- Vents
- Casing
- Included accessories and cables
The appearance of the equipment can tell you a lot, but it should not be the only factor in making your purchase decision.
For a broader checklist covering used test equipment, see the Used Test Equipment Buying Guide.
Checking the Calibration and Testing
For professional test equipment, calibration is very important to ensure that accurate measurements or controlled signals are generated.
When considering a used signal generator, look for calibration or testing data.
The level of accuracy required for the intended use will dictate the importance of calibration.
Service and testing information should also be reviewed.
Check the Included Accessories
The value and utility of used equipment can be increased or decreased by the availability of accessories.
Examples of accessories are:
- Power cables
- Output cables
- Adapters
- Connectors
- Manuals
- Rack-mount hardware
- Other manufacturer specific accessories
- Software
Prior to purchasing, determine which accessories come with the equipment and if they are of use in the application for which the equipment is being purchased.
New vs. Used Equipment
There are advantages of purchasing both new and used equipment.
Purchasing new equipment, provides the latest features and functions, and assures the equipment has a manufacturer’s warranty and support.
Used equipment can provide the purchase with the means to utilize professional equipment at a lower cost, especially if the used equipment meets the requirements of the application, and is no longer state of the art.
When evaluating equipment, the focus should not be on whether the equipment is new or used.
A properly evaluated used instrument can be suitable for many laboratory and engineering applications.
What to Ask Before Buying
What is the difference between a function generator and an arbitrary waveform generator?
A function generator produces standard repetitive waveforms such as sine, square, triangle, and ramp signals. An arbitrary waveform generator provides greater flexibility and can produce user-defined waveforms for more specialized testing applications.
What is a function generator used for?
A function generator is used to produce electrical waveforms for testing and troubleshooting electronic circuits and devices. Common applications include amplifier testing, digital circuit testing, laboratory work, repair, and development.
When should I use an arbitrary waveform generator?
An arbitrary waveform generator is useful when the required signal is complex, irregular, or needs to be customized. It can also be useful when an engineer needs to reproduce a waveform captured from a real-world electronic system.
Are RF signal generators and function generators the same?
Not always. RF signal generators are designed for radio-frequency applications and may provide specialized frequency, modulation, purity, and output capabilities. A general-purpose function generator may be intended for other applications.
What should I check when buying a used signal generator?
Check the model and specifications, physical condition, buttons, knobs, connectors, vents, casing, included accessories and cables, calibration or testing information, service history, and warranty or return policy.
Can a used signal generator be used for laboratory testing?
Yes. A used signal generator can be suitable for laboratory testing if it meets the required technical specifications and its condition, testing, calibration, and service information are satisfactory.
What specifications are important when choosing a signal generator?
Important specifications can include waveform fidelity, frequency range, peak output amplitude, sample rate, memory depth, modulation capabilities, and the accessories supplied with the instrument.
What is waveform fidelity?
Waveform fidelity refers to how faithfully a signal is reproduced. The required level of waveform fidelity depends on the application and the type of testing being performed.
Why is sample rate important for arbitrary waveforms?
For arbitrary waveforms, sample rate can affect how accurately the instrument reproduces a waveform. Depending on the application and other characteristics of the instrument, a higher sample rate may allow a waveform to be reproduced with greater fidelity.
Why is calibration important when buying used test equipment?
Calibration can be important when accurate measurements or controlled signals are required. When considering a used signal generator, calibration or testing information can help the buyer evaluate whether the instrument is appropriate for the intended application.
Conclusion
A function generator can be a good choice for basic waveforms and repetitive testing. For testing with more complex and varied waveforms, an arbitrary waveform generator may be a better option.
When a signal generator is being considered for a test application, a number of aspects need to be assessed. These may include waveform generation and fidelity, frequency of operation, modulation, and output characteristics of the signal. Other considerations may include memory size, sample rates, and associated accessories.
When evaluating a used signal generator, the same considerations should be assessed.