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You need to test, we're here to help.

23 February 2018

Transmission Lines (Part II): More on Bandwidth vs. Rise Time

In the frequency domain (right), a near-ideal square wave displays predictable 1/f amplitude dropoff
Figure 1: In the frequency domain (right), a near-ideal
square wave displays predictable 1/f amplitude dropoff
We began this series about transmission lines by thinking about some pertinent principles and relationships that can help form our thinking about the topic. In particular, we'd covered the relationship between bandwidth and rise time and why we have this rule of thumb that says that bandwidth can be estimated using 0.35/10-90% rise time.

20 February 2018

Transmission Lines (Part I): Introduction

All oscilloscopes have a Cal output like the one pictured here
Figure 1: All oscilloscopes
have a Cal output like the
one pictured here
Somewhere on the front panel of almost any oscilloscope is a "Cal" reference signal output (Figure 1). That signal is really intended for adjusting the capacitance compensation screw to calibrate a 10X high-impedance probe, but most of us know it simply as the Cal signal. Have you ever noticed that the Cal signal's rise time seems to be highly dependent on the length of the cable attached to it, and maybe even wondered why?

16 February 2018

Probing Techniques and Tradeoffs (Part XI): Non-Ideal Situations

VP@Rcvr builds a transmission-line model to virtually move less-than-ideal probing points
Figure 1: VP@Rcvr builds a transmission-line model
to virtually move less-than-ideal probing points
In using an oscilloscope to investigate transmission-line performance, we often encounter situations in which we don't have the luxury of probing at the ideal location. Fortunately, there are software tools that enable us to virtually move our probing point close to the receiver.

12 February 2018

Probing Techniques and Tradeoffs (Part X): More Best Practices

Chip clips; they're not just for snacks anymore
Figure 1: Chip clips;
they're not just for
snacks anymore
In probing circuits, as with most endeavors, there are some best practices you can use to enhance your chances of obtaining optimal measurements. We began exploring this concept in our last post, and we'll continue here with more best practices.

09 February 2018

Probing Techniques and Tradeoffs (Part IX): Best Practices

The typical manner of using a hands-free probe holder can cause issues
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.

08 February 2018

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

Noise comparison of a Teledyne LeCroy D1605 probe and a competing model
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.

06 February 2018

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

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
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.