As we take the plunge into 2011, I thought it would be interesting to take a moment
and reflect back on the oscilloscope. The oscilloscope has come a long way in its 70+ year life span. The test and measurement industry’s most popular instrument, the oscilloscope was originally designed to enable viewing and evaluation of varying signal voltages.
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site
My job offers me a wonderful opportunity to test a variety of leading-edge products and technologies. In the past month, I have had the privilege of testing three different categories of cables.
In the copper cable world, it has become routine to perform cable impedance characterization. As signals get even faster, s-parameters like insertion loss and return loss are also called out. At even higher rates, near-end and far-end cross talk s-parameters are required to characterize their transfer functions even for short, 1m cables.
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site
The eye diagram is probably the most well-known signal integrity tool because it combines numerous signal integrity characteristics such as rise/fall, overshoot/undershoot, and voltage/jitter into a simple visual of the signal. As additional layers of signal analysis and abstraction are added, there is often the need to perform a sanity check to ensure correlation to the physical layer waveforms. A case in point is understanding how a bathtub curve relates back to the eye diagram.
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site.
A typical PLL has an LPF that rejects high frequency perturbations and “cleans up” the input clock signal. Once locked, a PLL is immune to frequencies above the loop BW. From this perspective, the PLL rejects high frequency jitter.
But what happens to a PLL inside a CDR receiver? The inherent operation of the PLL does not change in a CDR receiver. It will continue to behave like an LPF by tracking the low-frequency components of the input clock. Hence, the recovered clock will not track frequency components above the loop BW of the PLL. This is illustrated by the LPF red trace below.
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site.
The integrity of a Tx signal is relevant only as it pertains to how the Rx sees it. In previous posts, I discussed Tx and Rx emphasis techniques used to compensate for channel losses. In this blog, I will share a few important scope setups that allow you to best replicate the CDR in your Rx.
Loop BW
The loop BW acts like a jitter filter. Jitter frequencies below the loop BW are tracked and rejected. Jitter frequencies above the loop BW are passed to the Rx slicer/comparator. Silicon vendors compete by developing silicon that have essentially higher loop BW since that improves the signal integrity of the receiver, but there is often a cost associated with a larger loop BW.
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site.
There are few of us immune from the growing reliance on global engineering where we work with team members, vendors, and customers scattered across the globe. In this post, I will share with you some of the techniques to make distributed evaluation and characterization of signal integrity easier.
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site.
Summer has finally made it here to the Pacific Northwest. For anglers like me, our thoughts turn to visions of large herds of salmon stacked up at the mouth of the mighty Columbia River. Unfortunately, there is this one obstacle that sits between us and the fish: the “Graveyard of the Pacific,” aka the Columbia River Bar.
To safely navigate the Bar, understanding its impairments or wave conditions is critical. At this link, you will note in the “TODAY” section various impairments:
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site.
By itself, jitter analysis is by far the most misunderstood and perplexing signal integrity topic. This complexity is exacerbated by the various jitter analyzers available. Obviously most of these instruments are capable of doing much more than analyzing jitter, but for this post I will focus on some of the strengths and weaknesses for jitter analysis.
Real-time scopes
As the name implies, the architecture of these jitter analyzers is particularly well-suited for real-time, single-shot jitter analysis. The jitter measurements here include consecutive cycle-cycle measurements, contiguous SSC (spread-spectrum clocking) modulation profiles, and TIE (Time Interval Error) analysis. However, their inherent phase noise floor will not allow them to viably characterize ultra-low jitter laboratory grade synthesizers.
To read the rest of this article, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site.
Like most who read this blog, you know that the scope is the quintessential tool for general-purpose debug and electrical analysis. And I’d venture that most of you have a ubiquitous old scope lying around the house and/or lab somewhere.
Some folks have even made it their passion to collect information about some of these older scopes, as evidenced by these Web sites:
Classic Tektronix Scopes
Tektronix Resource Site
The Museum of Tek Scopes
AnaLog’s Tektronix T922R Service Notes
These vintage products from a different era were unique from the perspective that Tektronix built most everything in house—from the PCB, knobs, and switches, to the cathode ray tube, to the mechanical chassis.
To read the rest of this article, see my take on soccer and to read the 20+ comments generated on both soccer and on a favorite old oscilloscope, please visit my Scope Guru on Signal Integrity Blog, on EDN’s site.
Question: Being a Laser Engineer there are many times where I need to catch a pulse train of several hu
ndred pulses at a time. I am using a pulsing solid state laser operating anywhere between 10 and 20 Hz. The issue is that I need to catch every pulse and then be able to export the data to Lab View for processing and integration with a full test setup.
I am using a nanosecond photo detector to look at the widths of each pulse. I need a scope to be able to detect and record each pulse of the set of pulses and then be able to conduct some basic statistics on the data: min, max, average, standard deviation, # of pulses, etc.
Typical Characteristics of the lasers are:
The pulse shape is a Gaussian shaped pulse, and we would have 500 pulses each with a width of 8-12ns occurring at a frequency anywhere between 10-20Hz. If it was 500 pulses at 20 Hz total time would be 25 s, 500 pulses at 15 Hz would be 33.33 s, and 500 pulses at 10 Hz, would be 50 s. So, the total length of time depends on the number of pulses in the data set and the frequency of the pulsed laser.
Which scope would be best for me and is there one that I can control through Lab View?
Answer: First the good news–any Tektronix scope will work with Lab View. But, here are specifics about making the measurements you need to make.
There are two ways to go about making the measurements you want. The first way would be to use a lower end bench scope, single shot each pulse, then pull that into data into Lab View. Then you would need to re-arm the scope trigger before the next pulse would occur. That puts a lot of variables on the PC side to ensure that the scope would be re-armed fast enough to catch the next pulse.
What we would recommend is using a scope that has FastFrame Acquisition mode. This mode allows the Oscilloscope to handle (by setup) the number of pulses (trigger event) and the number of data points to store every trigger event. This allows for high resolution capturing of each pulse, without using up record length saving time in-between each pulse. The time of trigger is also stored very accurately. This acquisition mode was designed specifically for the type of acquisition you need.
The recommended Tektronix instrument with this feature is one of our DPO7000 series of oscilloscopes.
