Signal Generators: Working Principles, Types, and Applications

Overview: This article explains signal generators\' working principles, types, key features, and applications across industries, highlighting their role in testing and developing electronic and communication systems.

A signal generator is an essential electronic instrument widely employed across a wide range of fields such as communications, research, medicine, and electronic testing.

What Is a Signal Generator?

Signal generators are designed to produce electrical signals with highly precise characteristics, such as amplitude, frequency, phase, and waveform. Serving as both analog and digital devices, they generate specific signals and deliver them to a device under test (DUT) to test, validate, and troubleshoot circuit designs and electronic systems.

They offer remarkable flexibility, allowing users to customize output parameters including frequency, voltage, impedance, waveform type, and modulation. Modern examples, like those from Tektronix, as shown in Fig. 1, can generate an extensive variety of signals, ranging from analog to digital, ideal to distorted, and standard to custom waveforms. This makes them vital in the development, troubleshooting, and verification of electronic devices.

Fig. 1 AFG1022 Signal Generators &Amp; Signal Analysers by Tektronix. Source: oemsecrets

Key Components and Working of Signal Generators

Unlike simple oscillators, signal generators can produce both basic and complex waveforms, including sine, square, and triangle waves, as well as modulated signals. The key components and working principles of the signal generator are depicted in Fig. 2.

Fig. 2 Diagrammatic Illustration of the Working of the Signal Generator. Source: Applied And Computational Engineering

Oscillator

It generates a basic waveform, often a sine wave, which is then shaped and adjusted by the waveform generator. The oscillator provides a stable and consistent signal at a specific frequency. It's the foundation upon which more complex signals can be built.

Voltage Controlled Oscillator (VCO)

A VCO is a key part of a signal generator. The frequency it produces depends directly on the control voltage applied to it. After the VCO, a modulator circuit can be used to change the signal further, such as adding amplitude modulation.

Switches (FM ON/OFF, AM ON/OFF)

It selects the type of modulation to be applied to the signal:

• Frequency Modulation (FM)

• Amplitude Modulation (AM)

FM ON/OFF: When the FM switch is ON, the signal from the VCO is used, enabling frequency modulation. When OFF, the signal bypasses the VCO.

AM ON/OFF: When the AM switch is ON, amplitude modulation is applied. When OFF, amplitude modulation is not applied.

Mixer (X)

It combines multiple signals into one, likely combines the modulated signal with another signal (possibly from the oscillator directly, in the case of AM). The specific mixing process can vary depending on the design.

Amplifier

It increases the power or amplitude of the signal. The amplifier boosts the signal\'s strength, making it suitable for transmission or further processing.

Variable Attenuator

The attenuator allows the user to adjust the output signal's voltage level. This is important for testing devices that require signals of specific amplitudes. The "variable" term means the amount of attenuation can be adjusted.

Output

Provides the final processed signal for use in testing or other applications. This is the point where the generated signal is sent to the DUT or other equipment.

Types of Signal Generators

Signal generators come in several types, each designed for specific testing needs.

Function Generator

It is a device that can produce a set of basic waveforms, such as sine, square, and triangle waves. Users can easily adjust settings like frequency, amplitude, and offset used for general testing and troubleshooting of circuits. An arbitrary function generator, as shown in Fig. 3, is a more advanced version that can create not only standard waveforms but also custom, user-defined waveforms. This allows for precise signal reproduction and the ability to add specific distortions or signal variations as needed.

Fig. 3. Arbitrary Function Generators AFG31000 Series. Source: Tektronix

Arbitrary Waveform Generator (AWG)

Unlike standard function generators, which produce only basic waveforms, AWGs can generate virtually any waveform shape by specifying voltage values over time. It creates custom, user-defined electrical waveforms with key characteristics including signal fidelity, memory depth, and sample rate. This makes them ideal for testing and simulating complex electronic circuits and communication systems that require precise or non-standard signals.

Pulse Generator

Unlike function generators, which typically output continuous waveforms, pulse generators are specialized for creating pulses with adjustable parameters such as pulse width, rate, amplitude, and rise and fall times. They are essential tools in laboratories for applications where specific, well-defined pulses are needed rather than continuous waveforms.

RF Signal Generator

These devices produce signals in the radio frequency range, typically from a few kilohertz (kHz) up to several gigahertz (GHz). They are important for component tests, receiver testing, EMC testing, avionics, and military radar applications.

Vector Signal Generator

It is an advanced RF signal generator that produces complex, digitally modulated signals with precise control over amplitude and phase. It supports modern modulation formats like QAM and OFDM, making it essential for testing wireless communication systems such as Wi-Fi and LTE. VSGs simulate real-world signals and impairments in the development and testing of RF receivers and transmitters.

Applications

Signal generators play a key role in general testing, communications, research, and medical applications. In communications, signal generators help test wireless (including mobile phones, WiFi, GPS), transceivers, satellite links, and fiber optics, simulating real-world conditions and assessing system performance. In research, they support studies in radar, electronic warfare, and signal processing in developing new technologies.

Summarizing the Key Points

• Signal generators produce highly precise electrical signals with adjustable parameters such as frequency, amplitude, modulation, and waveform type, essential for testing electronic systems.

• There are various types, including RF, vector, arbitrary waveform, function, and pulse generators, each for specific testing scenarios like wireless communications and circuit development.

• Key components like oscillators, VCOs, modulators, amplifiers, and > variable attenuators work together to generate, shape, and control > signals for different applications across industries.

Reference

Oemsecrets. (n.d.-a). AFG1022 Tektronix Prices & inventory - Signal generators & Signal Analysers | Oemsecrets.com. oemsecrets.com. https://www.oemsecrets.com/details/afg1022

Oemsecrets. (n.d.-b). AFG31000 - Compare distributor prices & inventory | oemSecrets.com. oemsecrets.com. https://www.oemsecrets.com/compare/AFG31000%20

Liu, Y. (2024). The signal generator: A critical analysis of its basic principles, applications, and development. Applied and Computational Engineering, 42(1), 27--33. https://doi.org/10.54254/2755-2721/42/20230678

Rohde & Schwarz. (2020b, July 2). Understanding signal generators [Video]. YouTube. https://www.youtube.com/watch?v=d3qxHB0XQxc

Signal generator. (n.d.). Tektronix. https://www.tek.com/en/products/signal-generators

Types of signal generators. (n.d.). Tektronix. https://www.tek.com/en/blog/types-of-signal-generators?bpv=2