Choosing a High-voltage Oscilloscope Probe for SiC/GaN Power Semiconductor Device Measurements

Figure 1: Wide-bandgap (GaN) power semiconductor device
waveforms captured using two, different probe topologies.
Click on any image to expand.

In our last post, we introduced you to a new tool on the Teledyne LeCroy website: The High-voltage Probe Selection Guide. To demonstrate the benefits of the guide, let’s explore further what must be considered when choosing an HV oscilloscope probe for power semiconductor device measurements.

Why are power semiconductor device measurements challenging?

How to Choose the Best High-voltage Oscilloscope Probe in 5 Minutes

Figure 1: The High-voltage Probe Selection Guide
color codes better or worse probe selections based on
your answers to three, simple questions.
Click any image to enlarge.

Probing high-voltage (HV) circuits for analysis with an oscilloscope presents unique challenges due to the potential for injury or equipment damage, as well as the demands of the materials used in HV semiconductors. HV floating measurements are extremely dangerous and difficult to make. Conventional passive probes are not the answer, but isolated and high-voltage differential probes are options. Yet, with many possible choices in these categories, how can you decide which is actually the best HV oscilloscope probe for your application?

Teledyne LeCroy offers this new, easy way to help you select a high-voltage oscilloscope probe based on your specific application—the High-voltage Probe Selection Guide—available on the Teledyne LeCroy website at: teledynelecroy.com/powerprobes

9 Quick Fixes to Improve DDR Probing

Figure 1: Reversed Handsfree mounts and chip
clips help relieve strain on fragile solders.

Probing at DRAM pins as required by JEDEC can be challenging. Here are nine, simple ways to improve your DDR probing.

1. Use positioning tools to relieve strain on probe tips

The Handsfree probe holder included as an accessory with several Teledyne LeCroy probes, such as the WaveLink and DH Series probes, was originally designed to put weight on the probe tip to ensure a good contact. However, many DDR probing applications utilize solder-in (SI) tips, where the greater concern is to relieve strain on the tip so as to not disrupt the solder. It turns out that if you use the Handsfree in a “reverse mounted” orientation (Figure 1), it puts the amplifier in a perfect position to help relieve strain on probe tips.

How to Test the CMRR of Differential Probes

Figure 1: CMRR plots for two attenuation
settings of an HVD3106A differential probe.

While recently we told you not to connect two probes to the same place at the same time, there is a case where connecting two tips of a differential probe to the same place at the same time is useful, and that is when testing the probe’s common mode rejection ratio (CMRR). CMRR is frequency dependent, so part of developing “situational awareness” of your test environment is to know how your probe behaves with different signals at different frequencies. 

Although CMRR as a function of frequency is a principal specification for differential probes, manufacturer's CMRR plots are the result of testing with a narrowband source under strictly controlled laboratory conditions. In real-world applications of probes to broadband sources, you can expect a different result. This quick test will inform you how different.

Basics of Power Conversion: Power Semiconductors

Figure 1: The basic building blocks of power
conversion circuits are the power MOSFET and
the IGBT; shown are (left) an N-channel
enhancement-mode MOSFET and (right)
a P-channel (minority carrier) IGBT

There are a multitude of circumstances that make power conversion a necessity. Power conversion, of course, is the converting of electric power from one form to another, from one voltage to another, or one frequency to another; it also encompasses any/all combinations of these.

Putting Probes in Perspective

Figure 1: Probe, cable, and oscilloscope form a system
that makes or breaks the accuracy of signal acquisitions

Few aspects of using an oscilloscope are as important as the probe: after all, the probe forms both the mechanical and electrical interfaces between the device under test (DUT) and the oscilloscope itself. To feed a signal into an oscilloscope, we're limited to a coaxial connection. Thus, we need a geometry transformer that picks up the signal of interest from the DUT and transfers it to the oscilloscope's coaxial connection.

Probing Techniques and Tradeoffs (Part IX): Best Practices

Figure 1: The typical manner
of using a hands-free probe
holder can cause issues

Having covered many of the theoretical aspects of probing signals, it's now useful to cover some best practices for high-speed active probing. We'll use some examples involving probing of DDR memory to illustrate what works best and what might not be a good idea from a practical standpoint.

Probing Techniques and Tradeoffs (Part VIII): Gain/Attenuation vs. Noise

Figure 1: Noise comparison of a
Teledyne LeCroy D1605 probe and
a competing model

When discussing oscilloscope probes and dynamic range as we've been doing of late, we must also touch upon the associated topics of internal gain/attenuation and how that relates to noise.

Probing Techniques and Tradeoffs (Part VII): More on Dynamic Range

Figure 1: Input offset range is how much
differential offset a probe can apply to
an input signal to bring it within its
differential-mode output range

In our last post in this series, we'd begun discussing the third of three types of dynamic range as applied to probes, and that is input offset range. This is the maximum differential offset that a probe can apply to the input signal to bring it within the probe's differential-mode dynamic range.

Probing Techniques and Tradeoffs (Part VI): Dynamic Range

Figure 1: Differential-mode dynamic range is the maximum
allowable voltage between the probe amplifier's inputs

We've been discussing probe loading, which is the unavoidable reality of what happens when you attach an oscilloscope probe to a live circuit. We'll now shift the discussion to dynamic range, an important topic that can be overlooked when selecting an oscilloscope probe. There are three types of dynamic range that one should understand. Each of them will influence how you set up your probe and how you set up your signal under test to most effectively get that signal into the oscilloscope's front-end amplifier.

Probing Techniques and Tradeoffs (Part IV)

Figure 1: Applying bandwidth filters to a 2.5-GHz clock
signal clearly shows the effect of bandwidth on rise time

The topic of probe bandwidth is a broad and deep one. We began our discussion of bandwidth in an earlier post with some basic information about what bandwidth means and the importance of the -3 dB point. Next, we looked at a Fourier deconstruction of a square wave into its fundamental and the lower-order harmonics, and covered the importance of bandwidth in capturing enough harmonic content to understand the signal's overall shape.

Video: The Many Varieties of Oscilloscope Probes

Got a minute (OK, a minute and a half)? Take a look at this quick tutorial video that takes you through the four basic types of probes and what they're used for:

If this little thumbnail sketch whetted your appetite for more info on oscilloscope probes, we've got you covered with a series of popular blog posts on the topic:

The Realities of Oscilloscope Probes

Back to Basics: Probes (Part I)

Back to Basics: Probes (Part II)

Back to Basics: Probes (Part III)

Back to Basics: Probes (Part IV)

Understanding Probe Calibration Methods

Understanding Probe Calibration Methods (Part II)

The Effects of Passive Probe Ground Leads

Back to Basics: Probes (Part IV)

Figure 1: An example of
differential probes
measuring from test
point to test point.

In three earlier posts on the basics of oscilloscope probes, we've taken a broad overview approach, looked more deeply at passive probes and inductance effects, and most recently, dug into active probes. Next up is differential probes, a different animal entirely from the foregoing types.

Back to Basics: Probes (Part III)

Figure 1: Active oscilloscope probes
sport high resistance and low
capacitance at their tips, but
terminate into a scope's 50Ω input.

In the first two installments of this series on probe basics, we examined some broad probe categories (Part I) and some of the issues that come with probe inductance (Part II). In the present installment, we'll delve a bit deeper into the topic of active probes. We'll also discuss when it's best to use passive probes and when to use active types.

Back to Basics: Probes (Part I)

Figure 1: An example of an active

oscilloscope probe 

To speak of an oscilloscope probe is to open a fairly large can of worms. There are many kinds of probes on the market, with differing functions and characteristics (Figure 1). This is the first in a short series of posts on the basics on probes, what the various kinds are used for, and how they might be expected to affect measurements taken with them.

Back to Basics: Differential Probing

Figure 1: Emitter voltage measurement
in simplified schematic view

Whether or not we think of it in such terms, any voltage measurement taken with an oscilloscope or voltmeter is, in reality, a differential voltage measurement. A voltage is, by definition, the difference in electrical potential between two points in a circuit. It's impossible to take a voltage measurement with only one voltmeter lead. One lead must be attached to the point of interest while the other must be connected somewhere else as a reference point.