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

24 July 2014

How Many Channels is Enough?

A switch-mode power supply driving a fixed load can be designed and optimized specifically for that load.
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.

When power-supply loads vary, so does efficiency, a scenario common in computing tasks.
Figure 2: When power-supply loads vary, so does
efficiency, a scenario common in computing tasks.
Consider the basic embedded switch-mode power supply. A simplified implementation might require only a single-phase current controller such as ON Semiconductor's NCP81141, a device with an Serial VID (SVID) interface for desktop and notebook CPU applications. SVID, by the way, is the communications protocol  Intel concocted for its VR12/VR12.5 specification for PWM control.

In a fixed-load scenario, a switch-mode power supply may be purpose-built for the specific application and thus be highly efficient, on the order of >90% (Figure 1). A device like the NCP81141 would be employed to regulate the current delivered to the supply while maintaining a constant voltage.

Figure 3: A multi-phase switch-mode controller dynamically
switches in more phases are required to service
a variable load.
However, in computing and other embedded applications, the load is anything but fixed, but rather is widely variable (Figure 2). Power control devices have a tough time optimizing the supply's efficiency with large load variations. The "sweet spot" for maximum efficiency is now a moving target. When the load changes and efficiency varies, the result is increased heating and stress on the power supply's components. Moreover, battery performance is compromised in portable systems.

The answer to this is a multi-phase controller such as ON Semiconductor's NCP81140, which dynamically switches multiple phases in (or out) depending on load changes (Figure 3). The response from such a device to changing loads is very fast, whether it is adding phases to shore up current to increasing loads, or shedding them when a single phase is able to keep up with the power requirements. In this fashion, high efficiency is maintained across the load spectrum with a huge corresponding reduction in heat stress on the supply's components. Moreover, the circuit is scalable in terms of the number of phases and the output per phase.

Proper debugging of this four-phase power supply circuit requires six oscilloscope channels
Figure 4: Proper debugging of this four-phase power supply
circuit requires six oscilloscope channels
The debugging of a multi-phase switch-mode power supply design would be difficult to undertake with the typical four-channel oscilloscope. The circuitry is considerably more complex than that of a single-phase power supply (Figure 4). In this case, debugging would call for six probes: four for monitoring the output currents of the four phases, and two more to monitor the overall voltage and current.

It gets even more complex when the power supply is for a server. Such power supplies call for six phases, so you'd be looking at eight channels. There are many other embedded applications for multi-phase switch-mode power supplies as well.

One example of an oscilloscope well suited for an application of this nature is Teledyne LeCroy's HDO8000 series, which sports eight analog input channels as well as 16 digital channels as an option.

18 June 2014

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.

09 June 2014

Video: Vertical Controls on the HDO Oscilloscopes

Here's another in our continuing series of tutorial videos. This time, we'll review the use of the vertical controls on a Teledyne LeCroy HDO oscilloscope. These controls facilitate positioning and scaling of waveforms vertically on the oscilloscope's display. Note that although we're demonstrating these controls on an HDO, you'd be rather hard pressed to find an oscilloscope from any manufacturer without a volts/div and vertical offset control. Thus, this video is applicable to whatever oscilloscope you have on your bench.

There are quite a few tutorial videos for a broad range of Teledyne LeCroy products on our YouTube channel. Head on over whenever you need a refresher!

22 May 2014

The Effects of Passive Probe Ground Leads

Teledyne LeCroy's PP108, a representative passive probe
Figure 1: Teledyne LeCroy's PP108,
a representative passive probe
When you open the box containing your shiny new oscilloscope, one of the items you'll likely find inside is a set of basic 10:1 passive probes (Figure 1). Those probes have a ground lead that you'll want to use when you make measurements. Your probe has a bandwidth specification that's probably somewhere between a few hundred megahertz to 1 GHz; that spec was obtained at the factory with a specialized test jig having a specific ground inductance and source impedance. Now, the way in which you connect your ground lead can have a big impact on the real-world bandwidth and response of the probe.

15 May 2014

Back to Basics: S-parameters

S-matrices for one-, two-, and three-port RF networks
Figure 1: S-matrices for one-, two-,
and three-port RF networks
Suppose you have an optical lens of some sort onto which you shine a light with a known photonic output. While most of the incident light passes through the lens, some fraction of the light is reflected and some is absorbed (the behavior is also dependent on the wavelength of the incident light). You'd like to characterize that lens: Exactly how much light was reflected? How much passed through? What is it about the lens that prevented all of the light from passing through?

07 May 2014

VIDEO: Horizontal Controls on the HDO Oscilloscopes

In the first of two posts on how to control the Teledyne LeCroy HDO oscilloscopes, we cover a good deal of ground relative to the front-panel controls. One of the topics is the horizontal controls, which position and scale acquired waveforms horizontally on the instrument's display. In this short video, application engineer Jeff Krauss takes you through the application of the time/div and horizontal delay controls so as to best position your waveforms for optimal viewing.

16 April 2014

Is Your Testbench Mixed-Signal Ready?

A representative block diagram of a mixed-signal embedded system
Figure 1: A representative block diagram of
a mixed-signal embedded system
Mixed-signal design is ubiquitous these days, with hybrids of digital and analog circuitry turning up everywhere. A typical mixed-signal designer may be a hardware or software engineer with specific needs. They may be working with 4-bit, 8-bit, 16-bit, and 32-bit microcontrollers in a single embedded controller or across several embedded systems. They need to capture a host of different signal types and serial-data protocols and understand timing relationships between them. Then there's all the different sensor signals, power-supply signals, and PWM control signals to guarantee embedded system performance and reliability.