Essential Features of a Good Waveform Tool for Electronic Testing

Key takeaways:

• Waveform tools are indispensable for creating detailed analog carrier and modulated signals, but they may be less useful for modeling purely digital signals.
• Waveform sequencing is a key feature that allows a library of waveforms to be maintained and reused across teams and projects.
• The number of supported test instruments and level of integration differentiates a good waveform tool from a mediocre one.

In every electronics project, test workflows involve the simulation of a variety of input signals to put the test circuits and equipment through their paces. These signals must be highly detailed to simulate the real-world conditions the devices may encounter during their operational lifetimes.

This calls for graphical editor-like applications that allow a waveform to be sculpted and specified to a high level of detail. These applications are called waveform tools. In this blog, find out the essential features and capabilities of good waveform tools.

A waveform tool enables design and test engineers to create complex waveforms for analog signals with fine-grained control over their shapes, durations, frequencies, phases, number of cycles, rise times, fall times, and other characteristics.

Such waveforms are created for playback on test instruments that generate raw waveforms or full-fledged signals. They are often combined with other components like modulated data to simulate input signals for devices under test (DUTs) whose behaviors and responses can then be studied.

The waveform data can be exported to a variety of test instruments like:

To provide a high level of fine-grained control over signal shapes, good waveform tools must implement the essential features outlined below.

Add basic and advanced shapes

Fig 1. Basic waveform shapes

Engineers must be able to build waveforms by assembling shapes that are common in electronic testing. These include basic shapes like:

• sine, half-sine, and haversine waves
• triangle/sawtooth shapes
• square and pulse shapes
• linear, ramp-up, ramp-down, and trapezoidal shapes

Fig 2. Advanced shapes

The ability to quickly insert complex segments that are common is a definite plus. They include:

• exponential rise and fall segments
• logarithmic shapes
• sinc function shapes
• damped oscillation segments
• multi-tone signals
• sweeps with start and stop frequencies
• Gaussian distributions
• Lorentz segments
• stair step segments

Draw arbitrary shapes

Fig 3. Arbitrary shapes

Many real-life signals include intricate shapes that can’t be represented by any of the predefined shapes. Good waveform tools must provide the ability to conveniently sculpt custom shapes by allowing:

• a set of arbitrary points, with control over how the samples are interpolated between those points, such as linear, smooth, step, or other interpolation
• free-hand drawings

Control waveform characteristics

For each shape segment, a waveform tool must allow the user to control its general and specific characteristics like:

• duration of the segment
• shape-specific timing parameters, like rise time and fall time for pulses or the time constant for exponential segments
• number of samples that make up the segment
• number of repeating cycles of the shape
• frequency of repetition
• peak-to-peak amplitude of the shape
• offset voltage
• phase of the segment

Edit waveform shapes and characteristics

After assembling the shape segments, users must be able to edit them like a graphics editor. Important editing capabilities include the following:

• select any portion of the waveform for subsequent editing
• cut, copy, paste, and delete selections
• normalize, scale, clip, or invert amplitudes
• time-related (X-axis) transformations like mirroring, trimming, shifting, rotating, and resampling segments
• frequency filtering transformations like the different low-pass, high-pass, and band-pass filters, like Kaiser and Butterworth
• frequency windowing operations like Gaussian and Hamming

Create sequences of waveforms

Fig 4. Waveform sequencing

Waveform sequencing enables you to assemble multiple waveforms with control over their order and timing. It essentially allows the reuse of created waveforms for multiple tests.

Apply math operators

Fig 5. Waveform addition of ramp shape to a sine shape

Basic math operations like addition, multiplication, and subtraction of one segment’s amplitude with the amplitudes of another segment should be possible.

Specify arbitrary equations

Fig 6. Equation editor

An important feature is an equation editor that allows users to express shapes using mathematical expressions and interprets the equations to plot the shape segments. This is useful for circuits or subsystems that are characterized by well-known mathematical equations, such as the resistor-capacitor (RC) circuit.

Add noise and distortions

Fig 7. Noise

The ability to add noise, distortions, and glitches is essential because they’re so common in real-life electronic and electrical equipment.

Visualize frequency-domain aspects

Fig 8. Frequency-domain visualization

Many radio frequency (RF) applications require engineers to visualize waveforms based on their power versus frequency characteristics. So although time-domain mode is the default, good waveform tools must provide frequency-domain analyzers and visualizations like:

• power versus frequency graphs
• Fast Fourier Transform (FFT) operations to convert from time to frequency domain
• inverse FFT for frequency domain to time domain conversions

Upload waveforms to instruments

Waveform tools must provide the following instrument control features:

• seamless detection and identification of the connected instruments and their characteristics like the number of channels and maximum sampling rate
• ability to upload the created waveforms to the specified instruments

Additionally, good tools must allow the downloading of waveforms from supported instruments to allow convenient editing on a computer before uploading them to the same or other instruments.

One way to enable wide support for instruments, both existing and future ones, is by implementing a plugin system and publishing application programming interfaces so that instrument vendors can integrate with these tools. Instrument connectivity standards like the virtualinstrument software architecture (VISA) already implement such a plugin-based ecosystem to support future instruments.

Fine-grained control over the waveforms requires some essential graphical user interface features like:

• displaying the instantaneous amplitude and timestamp at the position of the mouse pointer
• zooming in and out along the vertical and horizontal axes to see waveform points in more detail
• zooming into a selected portion of the waveform to view it in more detail
• adding cursors along both axes to mark amplitudes or time events of interest
• scaling the axes to provide the desired level of detail for users

Waveform tools are best suited for complex carrier and modulated analog signals. Some of their domain uses are listed here:

• Defense and aerospace: Waveform tools enable the creation of analog signals required for testing radars, power supplies, and avionics components. They also enable the testing of electromagnetic interference and electromagnetic compatibility by generating waveforms that mimic those problems.
• RF: Wi-Fi and other such wireless testing are possible by modeling their carrier signals, interference signals, and noise using waveform tools.
• Telecom: Similarly, waveform tools help the modeling of radio communication in 4G long-term evolution (LTE), 5G, and 6G access networks.
• Photonics: Waveforms are created for testing analog electrical signals and interference in photonics and fiber optic applications.
• Automotive: Automotive signals like radar chirps, power supply outputs, and battery charging inputs as well as their glitches and distortions can be modeled using waveform tools.

Most waveform tools provide the ability to create basic digital waveforms like pulse width modulated (PWM) signals. Some rudimentary binary encoding may also be supported.

However, for more complex digital modulation schemes like quadrature amplitude modulation (QAM) or phase-amplitude modulation (PAM), more specialized tools specific to the signal generator instruments are typically used.

Fig 9. Waveform representation

Waveform tools typically default to time-domain visualizations. The X-axis depicts time while the vertical axis indicates the amplitude, as shown above.

In alternative visualizations like frequency-domain views, the X-axis shows the frequencies and the Y-axis shows signal power in decibels or decibel-milliwatts.

Most of the shape segments require one or more of the offset, maximum, or minimum amplitude values as parameters to draw the shape. Waveform tools ask for these parameters based on the selected shape.

Additionally, waveform math operations like addition and subtraction involve specifying the amplitude parameters of the segment to be added or subtracted.

Frequency is often indirectly specified through the number of cycles of repetition of a segment. But for some shapes like multi-tone signals, the frequencies of the component tones must be specified by the user. The maximum supported frequency of a connected test instrument — in kilohertz (kHz), megahertz (MHz), or gigahertz (GHz) — as well as its other parameters (like maximum sampling rate and maximum number of samples) are determined either automatically by querying it or entered manually based on its datasheet.

Frequency-related editing operations include low-pass, high-pass, and band-pass filters; various windowing operations like Gaussian and Blackman windowing; and FFT conversion from the time domain to the frequency domain.

Frequency-domain visualizations are also provided.

Fig 10. Enter values directly as a table to create waveforms

For long complex waveforms, good waveform tools provide the following data management tools:

• Import data points from common file formats: These formats include comma-separated values (CSV), Microsoft Excel, and instrument-specific formats like .arb and .seq files.
• Import waveforms from instruments: These tools allow users to directly download waveform data from connected instruments over local area networks, universal serial bus connections, or general-purpose interface bus connections.
• Edit points as a table: The user can enter custom amplitude and timestamp values instead of trying to draw or plot them.
• Export waveforms to instruments: Waveform tools support the upload of waveform data to connected instruments.

Additionally, long repeating waveforms can be built as sequences of shorter waveforms. This allows the reuse of waveform data in memory as well, which helps when the datasets are large.

Some key considerations to keep in mind are outlined below:

• Instrument support: Does the tool support and integrate with all the instruments you plan to use?
• Sequencing features: Sequencing is a key feature that allows waveforms to be reused across teams and projects. Engineers with special knowledge of certain domains and devices can create a library of waveforms. Other test engineers can then reuse them across projects to optimize effort.
• Fine-grained control: Does the tool provide all the editing features you need to streamline your test plans?

Waveform tools enable the creation of intricately detailed signal shapes. This helps a variety of use cases like modeling:

• power supply output voltages
• sink inputs
• RF signals
• amplifier responses

These waveforms can be uploaded to the test instruments and blended with additional data like modulation signals to create full-fledged signals that can be used for testing.

These signals are replayed by testing instruments like arbitrary waveform generators and signal generators to simulate different operational conditions and events. The ability to create very detailed waveforms with very detailed noise and other anomalous characteristics allows in-depth testing of the DUTs to handle any operational conditions.

Make waves with the Keysight Waveform Builder Pro

Fig 11. Advanced waveform creation with BenchLink Waveform Builder Pro

In this blog, we gave an overview of the kind of capabilities that waveform tools must have.

Keysight’s BenchLinkWaveform Builder Pro is a powerful waveform tool that implements all the features we outlined so far. It’s a standalone licensed desktop application in the PathWave BenchVue suite and supports a wide variety of Keysight and other third-party instruments.

Contact us for help and technical support on our waveform tools and test instruments.