5 essential tools on an electronics bench

DC Power supply

Every electronic device requires power. Bench power supplies are important for the full test cycle - from the first turn-on to final verification. During turn-on, their current and voltage protections can save a faulty circuit board. During debugging, their data logging or electronic load capabilities can help solve power-related issues. Finally, their remote programming interface speeds up automated testing during final verification as well as production.

There are many DC power supplies available on the market, and all the choices can be overwhelming. Fortunately, there are only two basic power supply styles: linear and switching. These two types differ in how they regulate their output.

Linear power supplies are the ultimate low-noise source, but their power conversion is relatively inefficient. They are also somewhat heavy. (Hint: if you pick up the supply and it is “back heavy,” it is probably linear!) On the other hand, switched-mode power supplies have slightly more ripple noise, but they are much easier to move around a lab.

A modern switched-mode power supply is the best choice for most applications, as it offers the ideal combination of total output power, weight (ease of moving around the lab) and cost. However, some applications that have very sensitive ripple noise requirements may still require a linear power supply.

A bench power supply’s specification states the maximum available power output. If the supply has multiple channels, that maximum likely combines multiple channels. For example, the R&S®NGL200 one-channel model has a maximum output of 60 W, while the two-channel model has a maximum output of 120 W, but you must combine the two channels in series or parallel.

Modern power supplies offer many advanced capabilities beyond simple voltage and current controls. For example, “sense lines” are high-impedance lines that connect to the load. They allow the supply to compensate for ohmic losses in the power leads. In addition, data logging allows for relatively high-speed sampling of voltage and current directly to a USB drive for analysis. Some supplies can even function as an electronic load, which is perfect for simulating the charging and discharging of an IoT device battery.

Digital multimeter

A digital multimeter is also known as a DMM. An older name is a volt-ohm-meter (VOM), which usually refers to an analog-style meter. As the name "multimeter" implies, the instrument can measure multiple electrical properties, such as AC/DC voltage, AC/DC current, resistance, diode forward voltage and capacitance. Results are commonly given as an instantaneous value on a numeric display. However, some DMMs can also provide statistical information about a series of measurements. It should be noted that while DMMs are capable of multiple different measurements, they can typically only make one type of measurement at a time.

Digital multimeter specifications include precision and accuracy. The precision indicates what ranges of values can be displayed for measurements. The accuracy varies across measurement functions and ranges.

Some DC power supplies also have very accurate voltage and current meters built in, combining functionalities of a power supply and a digital multimeter. For example, the R&S®NGL200 is a two-channel power supply with a 6 1/2 digital meter for voltage, power and current.

Oscilloscope and AWG

An oscilloscope is also sometimes called a "scope." It measures voltage across time and plots it as a waveform. Natively, oscilloscopes only capture voltage, but with probes, they can also measure other quantities.

Oscilloscopes can be analog or digital, depending on how the waveform is acquired. The first instance of oscilloscope digital triggering was patented by Rohde & Schwarz and today, almost all oscilloscopes use digital triggering and a digital-to-analog converter to capture waveform data.

Once a waveform is acquired, oscilloscopes have extensive measurement and analysis capabilities. For example, voltage measurements can include peak-to-peak, top and base values in addition to RMS. Oscilloscopes can also measure multiple signal parameters simultaneously.

Oscilloscopes generally have at least 2 - and more commonly, 4 - input channels. These channels allow signals to be acquired simultaneously as well as viewed correlated in time (or phase).

Over time, oscilloscopes have developed features that allow them to replace other electronic test instruments. For example, all Rohde & Schwarz oscilloscopes have 8 or 16 digital logic channels, which can often replace a traditional logic analyzer. Some oscilloscopes, like certain models of the R&S®RTH1000, even integrate a complete digital multimeter.

Engineers commonly use arbitrary waveform generators (AWG), or function generators, with oscilloscopes. Many modern oscilloscopes offer a built-in AWG that can replace many stand-alone function generators. These scope-AWG combinations can use built-in software to perform important measurements and display the information in graphs like bode plots!

The FFT function converts an acquired waveform into a frequency display. Some oscilloscopes have hardware-accelerated FFTs, which perform similarly to a standalone real-time spectrum analyzer.

Spectrum analyzer

Spectrum analyzers measure a signal’s frequency content. They plot magnitude on the x-axis and frequency on the y-axis. The peaks identify the frequency components. In addition, some spectrum analyzers offer a spectrogram display to see how much time a signal occupies in different parts of the spectrum.

The typical spectrum analyzer is a sweeping type that has a superheterodyne receiver at its core. It sweeps the center frequency across a range, down-converting small portions of the input signal, one frequency unit at a time. The advantages of swept spectrum analyzers are high-frequency range, high sensitivity and extremely low noise floor.

Spectrum analyzers are also capable of automated measurements beyond measuring the frequency content. For example, they can measure channel power, occupied bandwidth, harmonic distortion, AM modulation depth and third-order intercept (TOI).

Some instruments, like the R&S®FPC1500, include a signal generator that can output a continuous wave (CW) signal across the analyzer’s frequency range. For example, the R&S®FPC can output up to a 3 GHz. Alternatively, the generator can track the analyzer’s sweep frequency. This tracking generator combination helps measure the transfer function of a device or, with an offset, mixers.

Application-specific tools

Finally, you may want some essential tools more specific to your application. For example, if you need to characterize passive components, you might use an LCR meter - sometimes called an “LCR bridge” or just a “bridge” for short. These tools measure the inductance, capacitance and resistance at different frequencies and DC bias points.

Vector network analyzers (VNAs) are another characterization tool that can provide the S-parameters of components such as cables, PCB traces and amplifiers. Related to VNAs are power sensors, which measure the power level of an RF signal and provide a numeric output.

A line impedance stabilization network (LISN) connects the device under test (DUT) with an AC source for EMC testing. The LISN has an output port that allows an EMC receiver to measure conducted emissions from the DUT.

Power analyzers measure the power consumption of AC/DC loads. Analyzers such as the R&S®HMC8015 are all-in-one tools that simplify the characterization of different power states, harmonic analysis and other switch-on behavior.

Form Factor and Class

All the instruments listed here come in multiple form factors and are available in different classes. Form factors include benchtop, handheld or rack-mounted. (In general, most benchtop instruments have rack mount kits available.)

Instruments tend to be grouped into different classes according to performance specifications or feature sets. While all of the tools within a class perform the same essential measurement, the required capabilities may vary by application. For example, oscilloscopes tend to be grouped by their bandwidth ranges, and you may need a particular bandwidth for your application.