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

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

22 July 2015

Debugging I2C Buses in Embedded Systems

Debugging of I2C on a Teledyne LeCroy WaveSurfer 3000 oscilloscope
Figure 1: Debugging of I2C on a Teledyne LeCroy
WaveSurfer 3000 oscilloscope
Embedded systems became ubiquitous decades ago and are now found in everything from mobile devices to vehicles to the traffic lights that control their movements. These days, they're typically based on microcontrollers and perform some specific task(s) within a larger system, such as controlling your car's ABS system. They may or may not have any sort of user interface, and can range widely in terms of complexity and functionality.

PAM4 Test Setups Vary With Applications

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In an earlier post, we surveyed the basic properties of PAM4 signals. Now, we will examine some of the ways in which PAM4 is finding application in the real world and what test and measurement setups might look like for those applications.

15 July 2015

The Fundamentals of PAM4

PAM4 doubles the number of bits in serial data transmissions by increasing the number of levels of pulse-amplitude modulation, but does so at the cost of noise susceptibility
PAM4 doubles the number of bits in serial data transmissions
by increasing the number of levels of pulse-amplitude modulation,
but does so at the cost of noise susceptibility
As our society's hunger for data grows—not only more data, but more data delivered faster—older modulation schemes based on NRZ-type encoding grow increasingly inadequate. We need to get data from point A to point B as efficiently as possible, whether that means between chips on a PC board or from one end of a long-haul optical fiber to the other. A modulation scheme that's gaining favor in many quarters is PAM4, and in this post we'll look at the basics of PAM4 before turning to the test and analysis challenges it poses.

08 July 2015

Using Persistence Mode and Exclusion Trigger

Figure 1: By using exclusion triggering, the oscilloscope
is prevented from triggering on the normal signal shape.
The trigger is set to capture only pulses with widths
different by at least 15 μs from the typical 325 μs.
Any piano player is well acquainted with the right-most pedal on their pianos, known as the sustain or open pedal. Pressing that pedal while playing will lift all of the instrument's dampers away from the strings, allowing them to ring freely until their vibration dies out or the pedal is released.

On a digital oscilloscope, the persistence display mode is a little like the sustain pedal on a piano. When persistence display is selected, the oscilloscope will trigger, display the signal trace, then trigger again and add another trace to the display, and so on.

25 June 2015

Don't Leave Oscilloscope Performance on the Table

Figure 1: In this screenshot, four signals are displayed
on a single grid. Each signal is only using
64 counts of its ADC, which amounts to 6-bit resolution.
As test and measurement companies add to their products' capabilities, digital oscilloscopes serve a larger and more sophisticated set of measurements as vendors have added to their capabilities. And even though many of those additions come at the behest of the user community, many oscilloscope users don't even scratch the surface of what their instrument can do.

16 June 2015

Device Analysis in Switch-Mode Power Supplies

Figure 1: Setup for analysis of switching losses
in a switch-mode power supply's MOSFET
Our survey of testing switch-mode AC-DC power supplies started by looking at the variety of measurements one might make on these devices and why differential probes and amplifiers are often the best choice over passive probes. Subsequently, we examined the key sources of error in power-supply measurements and how to minimize them. Now it's time to start taking some measurements with an eye toward device analysis, particularly the switching transistor in a switch-mode supply.

11 June 2015

Reducing Errors in Switch-Mode Power Supply Measurements

Figure 1: Skew between voltage and current probes
results in power measurement errors
Almost all portable electronic devices, and lots of non-portables, come with switch-mode power supplies. These range from common "wall warts" to the larger brick-sized supplies that power a laptop. We've taken a look at the typical measurements one might make on a switching power supply and at why single-ended measurement techniques should take a back seat to differential approaches. Now, let's see what steps we can take to ensure that our measurements on power supplies are accurate.