What Is a Function Generator? Waveforms, Controls and Uses

What Is a Function Generator? Waveforms, Controls and Uses

ByKen

What Is a Function Generator? Waveforms, Controls and Uses

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A function generator is a piece of electronic test equipment that produces repeating electrical signals of a chosen shape, frequency and amplitude. Engineers and technicians use it as a known input source. They apply its signal to a circuit or device, then watch what the device does with an oscilloscope or another meter. If you have ever wondered what the knobs on a signal source do, or why a lab bench almost always has one, this guide explains the basics.

The short answer is that a function generator supplies the input. A multimeter reads a voltage or resistance that already exists in a circuit. A function generator creates a signal that you choose.

Quick answer

  • A function generator outputs repeating waveforms, most often sine, square, triangle and sawtooth, at a frequency and amplitude you set.
  • It supplies the input to a circuit. An oscilloscope or meter measures the result.
  • Standard units make standard shapes. Arbitrary waveform generators add custom shapes, more modulation and higher precision.

What a function generator does

Tektronix describes its function generators as electronic test equipment that delivers signals to a device under test. The purpose is to test a design or to confirm that equipment works as intended. Keysight’s glossary uses similar language. It describes a function generator as an electronic device that produces repetitive waveforms over a broad range of frequencies, and it notes that engineers use the output as the input signal when they study a design’s response.

In practice, the workflow is simple. You set the waveform shape, the frequency and the amplitude on the generator. You connect its output to the circuit under test. Then you measure the result somewhere else in the circuit. The generator does not measure anything on its own. It is the source half of a test setup.

Waveform types

The standard shapes are the ones most people remember from a physics or electronics class. Keysight’s glossary lists sine, square, triangular and sawtooth patterns. Tektronix lists sine, square, pulse, triangle and others as standard waveforms. The overlap is clear: sine, square and triangle are the core set.

  • Sine wave: a smooth, repeating curve. It is the basic shape used to test how a circuit passes or filters a signal at a given frequency.
  • Square wave: a signal that switches between two levels. It is useful for checking how a circuit handles fast transitions.
  • Triangle wave: a signal that ramps up and down at a steady rate.
  • Sawtooth wave: a signal that ramps in one direction and then drops back. Keysight lists it with the standard shapes.
  • Pulse: a signal that stays at one level for a short time. Tektronix lists it among standard waveforms.

Keysight also notes that some units extend this set with other shapes, and that arbitrary units can produce any waveform that can be described mathematically. Those features belong to the more advanced class of instruments discussed later in this guide.

The main controls

Keysight’s glossary lists the common controls found on a function generator. They are the parts you will adjust most often.

  • Frequency control: sets how fast the waveform repeats.
  • Amplitude control: sets the strength or size of the signal.
  • Waveform selector: chooses the shape, such as sine, square or triangle.
  • DC offset control: shifts the average level of the wave up or down, so the signal can sit above or below zero volts.
  • Output connector: the port that delivers the signal to the external circuit.

Tektronix adds that many modern units also allow you to adjust characteristics such as symmetry, which changes how long the rising and falling parts of a wave last. Check the manual for your specific model, since the exact controls and their ranges differ between products.

Features beyond the basic wave

Tektronix’s arbitrary function generator page describes several extra features that many units offer. These go beyond setting a single steady wave.

  • Frequency sweep: the output changes frequency over time, which is useful for finding a resonance or the response range of a filter.
  • Modulation: the signal can be modulated from an internal or external source. Tektronix describes this alongside sweep and burst output.
  • Burst output: the generator produces a set number of cycles and then stops, rather than running continuously.
  • Fast frequency switching: the unit can change between frequencies quickly, which Tektronix calls a key strength.

Not every bench unit has all of these. Basic models are typically limited to standard shapes and simple controls. Feature lists vary by product, so compare the specification sheet for the exact model you are considering.

Function generator versus arbitrary waveform generator

Keysight’s used-equipment guide separates two related instruments. A function generator produces standard waveforms over a wide frequency range. An arbitrary waveform generator (AWG) can produce custom waveforms defined by a sequence of data points.

The guide compares the two on several points:

  • Waveform flexibility: an AWG can create custom shapes. A function generator is limited to standard shapes.
  • Frequency range: the guide says AWGs generally reach higher frequencies, up to GHz, while function generators top out at several MHz.
  • Precision: AWGs are rated high precision, while function generators are rated moderate to low.
  • Modulation: AWGs support a wider range of modulation types. Function generators are mostly limited to AM and FM.
  • Channels and connections: AWGs often have several channels and interfaces such as USB, Ethernet or GPIB. Function generators usually have one channel.
  • Cost and ease of use: AWGs cost more and take longer to learn. Function generators are cheaper and quicker to set up.

Keysight’s bottom line is that function generators suit simple, standard-waveform tasks such as education, basic repair and quick tests. AWGs suit custom waveforms, advanced modulation and high-precision research work. Many current units are arbitrary function generators, or AFGs, which keep the preset shapes and can also play custom ones.

Function generator versus oscilloscope

People often mix up these two instruments because they are used together. The generator is the source that creates the signal. The oscilloscope is the measuring instrument that displays it. A common setup connects the generator’s output to a circuit, then connects the oscilloscope probe to the point you want to see. The generator sets what goes in, and the oscilloscope shows what comes out.

Function generator versus multimeter

A multimeter reports a single number, such as volts, ohms or amps, at the point where you place its leads. A function generator makes a changing signal that you control. A multimeter does not create a waveform for a circuit. If your task is to check whether a voltage exists, a multimeter is the right tool. If your task is to apply a known waveform and see how a circuit responds, you need a generator.

Who uses one

The sources describe use in design, test and education. Tektronix presents its units as test equipment for checking designs and confirming that equipment works as intended. Keysight lists education, basic repair and quick tests as typical tasks for a standard function generator, and notes that engineers use the output as input when they study a design.

Choosing a basic function generator

Start with the waveforms you need. If sine, square and triangle cover your work, a standard function generator is enough. If you need a custom shape stored from a data sequence, look at AWG models. Next, check the frequency range. Keysight’s guide gives a rough range for standard units, but the exact upper limit depends on the model, so read the datasheet for the unit you plan to buy. Finally, check whether you need sweep, burst or modulation. Those features add cost and complexity, so only pay for what your tests use.

Common mistakes to avoid

  • Assuming every generator is an AWG. A standard function generator cannot play arbitrary shapes. Check the product class before buying.
  • Reading the frequency rating as a guarantee for every waveform. The sources describe typical ranges. Specific limits for a given waveform or mode belong in the manufacturer’s datasheet.
  • Confusing the generator with a meter. The generator supplies a signal. It does not tell you what a circuit is doing unless you connect a measuring instrument.

How we chose

We opened the Tektronix arbitrary function generator product page and two Keysight used-equipment pages, one glossary entry and one comparison guide. We used only the definitions, waveform lists, controls and feature descriptions those pages state, and we left out brand claims and sales wording. Where the pages gave no figure, we did not supply one.

What we could not verify

We did not find a Fluke Learn or Klein Tools page that defines a function generator in the same terms, so this guide relies on the Tektronix product page and two Keysight used-equipment pages. Exact frequency limits, amplitude ranges, sweep and burst specifications, and channel counts vary by model and are not given here. Check the datasheet for the specific unit you are considering. We also did not verify how any particular brand implements its modulation options.

Summary

A function generator produces standard repeating waveforms, most often sine, square, triangle and sawtooth, at a frequency and amplitude you set. It is the signal source in a test setup, while an oscilloscope or meter does the measuring. Basic models cover the standard shapes. Arbitrary waveform generators add custom shapes, higher precision and wider modulation at higher cost. Choose the class that matches the waveforms your work needs, then confirm the limits in the datasheet for the model you buy.

For a broader view of meters that sit beside a signal source on the bench, see our best multimeter guide and our clamp meter versus multimeter comparison.

Frequently asked questions

Is a function generator the same as a multimeter?

No. A multimeter reads a value at the point its leads touch. A function generator creates a signal that you choose and apply to a circuit.

What waveforms does a function generator make?

The sources list sine, square, triangle and sawtooth as the usual shapes, with pulse also named by Tektronix. Some units add other shapes.

What is the difference between a function generator and an arbitrary waveform generator?

A function generator makes standard shapes. An arbitrary waveform generator plays back user-defined data points, and Keysight rates it higher in precision and frequency range.

Do I need an oscilloscope to use a function generator?

The generator only produces the signal. To see how a circuit responds, you need a measuring instrument such as an oscilloscope or a meter.

Sources

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