Feature: T&M
Classifications Signal generators are classified based on their format and capabilities, with the most common being the benchtop type, which provide a single function that can’t be expanded. PXI Express (PXIe) modular signal generators are compact,
housed in a PXIe chassis and controlled by a PC. Multiple PXIe signal generators are in a single chassis, making them great for applications that require multi-channel measurements and a small footprint. PXIe sources are configurable with a mixture of analogue and vector signal generators. Tey can also offer the flexibility of multiple inputs and outputs by adding a vector analyser to the setup. Analogue signal generators supply sinusoidal continuous
wave (CW) signals with optional capabilities to add amplitude modulation (AM), frequency modulation (FM), phase, and pulse modulation. Vector signal generators (VSG) enable complex digital
modulation schemes, such as quadrature phase-shiſt keying (QPSK) and 1024 quadrature amplitude modulation (QAM). Tere are also agile signal generators that are speed optimised, for quick changes of the signal’s frequency, amplitude or phase. Lastly, there are vector signal transceivers (VST) that combine
Securing signal generator accuracy
By TJ Cartwright, Product Manager for analogue and digital RF signal generators, Keysight Technologies
a VSG with a vector signal analyser, giving the power to create a signal and analyse a device under test with one instrument. Playback mode options are only relevant to VSGs. Arbitrary and
real-time waveforms are the two options for generating signals; both are used for testing and validating. Arbitrary waveforms are shorter samples or pre-defined signals
stored on the signal generator, which also means the signal generator must have enough memory for the sample. Alternatively, a real-time waveform generator relies on soſtware to generate the signals for testing, removing the need for the signal generator to have internal memory to store waveforms. A good example of playback modes is the testing of a Global
Navigation Satellite System (GNSS) receiver. A GPS almanac is a requirement to start the process of locating satellites. Storing this on a signal generator would require a significant amount of memory, so a real-time generator is the best choice. However, testing a local oscillator doesn’t require a generated signal that lasts for an extensive period. In any case, a signal generator can’t meet every need, so
S
electing a signal generator for the first time can be challenging, since there are many attributes to consider and it is not always clear which features are the most important for the test requirements. Signal generators – or signal sources – provide precise, highly-stable and customisable test signals
for various components and sub-systems that emulate real-world scenarios. Outputs can be anything from a simple continuous wave to more complex, modulated, digital signals. Signal generators are an essential part of product development
because they mimic signal impairments for testing a product in various conditions.
24 June 2024
www.electronicsworld.co.uk
accessories are added to it to bridge any functionality gaps. Frequency extenders are just one example, and digital signal interface modules give users access to a source’s digital inputs and outputs.
Accuracy Many attributes determine the signal generator’s accuracy and preciseness, and knowing where to look for errors is essential. A signal generator’s amplitude and frequency accuracy, spectral purity and error vector magnitude (EVM) measurements are key sources of error. Amplitude accuracy compares the signal generator’s output to the desired amplitude set by the user. Consider the example of
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