Eliminate Pitfalls of DDR Memory Testing

Figure 1: DDR test configuration
for a desktop computer

Since its inception as a standard in the mid 1990s, dual data-rate (DDR) SDRAM memory has been near ubiquitous in computing applications. Compared to single data-rate SDRAM, the DDR SDRAM interface makes higher transfer rates possible by more strict control of the timing of the electrical data and clock signals.

Oscilloscope Basics: Using The Display Graticule

Figure 1: The display graticule, the grid of intersecting lines
overlaying the signal display area, is the original
oscilloscope measurement tool

Today's digital oscilloscopes come packed with an abundance of measurement capabilities, all available at the touch of a button or two. Want to know the amplitude of a square wave? Easy. Want to know the standard deviation of that amplitude? Minimum/maximum or mean? All easily compiled for you over hundreds or thousands of acquisitions.

Go Back to School on Signal Integrity

No matter how much we might think we know about signal integrity, there's always more to learn. The laws of physics never change but we might come across new scenarios in which to apply them. Circuits with higher levels of functionality are constantly being squeezed into smaller, more portable spaces; the closer together we pack active components and transmission lines, the more acute their sensitivity is to electromagnetic energy. Everything's either a transmitter or a receiver in some sense and everything has effects on other components, intended or otherwise.

Oscilloscope Basics: History Mode

Figure 1: Initial setup of WaveSurfer 3000 with a
2-MHz pulse waveform fed into Channel 1

Back in the day, one of the biggest deficiencies of early digital oscilloscopes was their lack of memory depth. A memory of 500 or 1000 points was about as good as it got, and this didn't provide much in the way of detailed waveform capture. Today's instruments are very different animals; for example, Teledyne LeCroy's recently introduced WaveSurfer 3000 oscilloscopes offer up to 10 Mpoints of memory per channel.

Video: WaveSurfer 3000 and the MAUI User Interface

Oscilloscopes are often an engineer's best friend, but that can change depending on how easy or difficult a given instrument is to use. Sure, the oscilloscope's capabilities and technical specs are critical, but if the machine is difficult or non-intuitive to interact with, the user ends up wasting time figuring out what should be simple.

How Many Channels is Enough?

Figure 1: A switch-mode power supply driving a fixed load

can be designed and optimized specifically for that load.

The bulk of oscilloscope applications are well served by instruments with four analog input channels. Most basic debugging and design-related work involves probing of only one signal at a given time, and occasionally more than one, especially when differential signals are concerned. Thus, many users may never see a need for an oscilloscope with more than four channels.

Having said that, there are some applications that by their very nature surpass four channels. Moreover, some of these applications concern circuits and devices that are produced in extremely high volumes. A case in point is switch-mode power supplies, such as those typically found in notebook PCs, tablets, or embedded systems.

Applying Selective Averaging to Waveform Acquisitions

Figure 1: Using pass/fail testing to average only those
waveforms which are inside the tolerance mask

In the course of using an oscilloscope, there are likely to be times when you'd like to separate pulses based on wave shape or some parametric value and average only those pulses that meet some criteria. Teledyne LeCroy's oscilloscopes, and others, provide pass/fail testing using masks and/or parametric readings to qualify waveforms before they're added into an average or other processing function. Let's take a look at how this works on a Teledyne LeCroy oscilloscope.