What Are Signal Generators?

Signal generators are instruments or circuits that produce controlled electrical waveforms for use in testing, calibration, and system design. They supply the stimulus that exercises a device under test, whether that device is an amplifier, a filter, a communications receiver, or an entire integrated circuit. By generating waveforms with precisely defined frequency, amplitude, phase, and modulation characteristics, signal generators allow engineers to characterize system behavior under repeatable, well-understood conditions.

The category spans a wide range of implementations: from simple function generators producing sine, square, and triangle waves to sophisticated arbitrary waveform generators capable of reproducing any digitally specified waveform, and from low-frequency audio oscillators to microwave synthesizers operating above 100 GHz.

Waveform and Arbitrary Waveform Generators

Waveform generators produce standard periodic waveforms, typically sine, square, triangle, and sawtooth, at selectable frequencies and amplitudes. Their internal architecture usually consists of a phase accumulator clocked by a stable reference, a lookup table mapping phase to amplitude, and a digital-to-analog converter (DAC) driving an output amplifier. Direct digital synthesis (DDS) techniques allow fast, phase-continuous frequency switching, which is valuable in frequency-hopping and chirp applications.

Arbitrary waveform generators (AWGs) extend the concept by allowing the user to define the output waveform sample-by-sample. A high-speed memory stores the waveform data, and the DAC replays it repeatedly at a programmable sample rate. AWGs can reproduce complex modulated signals, distorted waveforms for predistortion testing, or custom pulse shapes for radar and ultrasound applications. Keysight's application notes on arbitrary waveform generation describe practical considerations including sample rate, vertical resolution, and memory depth.

Noise Generators

Noise generators produce random signals with specified spectral density. White noise, whose power is distributed uniformly across frequency, is the most common type and is used to test audio equipment, measure system noise figures, and stress-test communication receivers. Colored noise generators shape the spectrum, for example to a 1/f (pink noise) profile for acoustic testing, or to a band-limited Gaussian distribution for channel simulation.

Noise figure measurements using the Y-factor method require a calibrated excess noise ratio (ENR), a quantity defined and standardized by NIST's RF measurement program. Traceable noise sources provide the reference against which receiver noise performance is compared.

Optical Pulse Generation

Optical pulse generators produce short bursts of laser light for use in fiber-optic communications research, time-resolved spectroscopy, and lidar. Mode-locked lasers generate pulse trains with repetition rates in the gigahertz range and pulse durations from picoseconds to femtoseconds. Electro-optic modulators driven by electronic pulse generators can carve pulses from continuous-wave laser sources with timing jitter in the sub-picosecond range.

Research on optical pulse generation and its applications in ultrafast science and high-capacity wavelength-division multiplexing appears regularly in Optics Letters and Optica, published by Optica Publishing Group.

Pulse Generation

Pulse generators produce rectangular pulses with controlled rise time, fall time, width, and repetition rate. They are essential for digital logic testing, where edges must meet specified timing margins, and for radar transmitter testing, where pulse compression ratios and chirp linearity must be verified. High-voltage pulse generators with nanosecond rise times are used in pulsed power research, plasma generation, and medical treatment systems such as irreversible electroporation.

Applications

Signal generators serve across a broad set of technical domains:

• Electronic test and measurement: signal generators drive device inputs during gain, linearity, and noise figure characterization.
• Communications system development: modulated signal generators produce realistic channel impairments for receiver sensitivity and selectivity testing.
• Radar and ranging: chirp and pulse generators provide the transmit waveforms that radar and lidar systems require.
• Biomedical instrumentation: function generators drive ultrasound transducers and stimulate neural tissue in research setups.
• Education and prototyping: benchtop waveform generators supply stable references during circuit development and student laboratory exercises.