DSO shoot-out
Tests on high-end DSOs from LeCroy and Tektronix leave performance questions unanswered.
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 3/1/2003
On October 29–30, 2002, T&MW joined sibling publication EDN magazine in hosting a shoot-out of real-time-sampling oscilloscopes from LeCroy and Tektronix. The goal: Find out which scope could more quickly perform measurements ranging from simple to complex. We did not want to compare the scopes' bandwidths or sampling rates, but rather their ability to process measurements and produce useful data. Although the test results show LeCroy coming out on top, they might have been different had Tektronix sent a technical representative to the event. You can read the full story about the shoot-out in the February 6 issue of EDN (www.tmworld.com/edn).
The setupEDN senior technical editor Dan Strassberg proposed and organized the event (Figure 1). He invited each company to send a 6-GHz real-time sampling oscilloscope and two representatives to our offices for the shoot-out; at least one of the representatives was to have an in-depth knowledge of his or her company's scope. Strassberg also asked both companies to propose six tests for the shoot-out. Lack of time and an inability to perform all tests on both companies' scopes limited the tests to those listed in Table 1 .
LeCroy agreed to bring a 6-GHz Wavemaster 8600A, and Tektronix agreed to bring a 6-GHz TDS6604. Tektronix also proposed bringing a CSA7404, a 4-GHz deep-memory scope that offers features for analysis of serial-data signals; LeCroy agreed to Tek's proposal.
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Figure 1 EDN senior technical editor Dan Strassberg (left) and Test & Measurement World executive editor Rick Nelson review a measurement. Photo by Joshua Israelsohn. |
As part of the rules, each company agreed to allow the other ample time before the shoot-out to evaluate the scopes. Shortly before the shoot-out—and too late for Tektronix' engineers to evaluate it—LeCroy announced a serial-data measurement (SDM) option for the 8600A. In lieu of the SDM, LeCroy proposed using a jitter and timing analysis option, the JTA2, that the company introduced with the Wavemaster in March 2002. The SDM and JTA2 options have much in common, although the newer option offers more features and performs several analyses faster than does the JTA2. Because the JTA2 could perform all of the tests that Tektronix had proposed, LeCroy offered to disable the SDM option on the 8600A it brought—something that a user can do from the scope's main menu—but Tek insisted that LeCroy not bring a scope with the SDM option installed at all.
Because it couldn't evaluate the SDM option in time for the event, Tektronix claimed that LeCroy had violated the rules. Hence, Tek withdrew from the shoot-out. Nevertheless, the tests went on. LeCroy brought a4-GHz TDS7404 that it owns, a rented Tek TDS6604, and a LeCroy Wavemaster 8600A with the SDM option. (The TDS7404 included Tek's JIT3 option. With this option installed, the TDS7404 is quite similar to the CSA7404 that Tek had asked to bring.) In the end, the tests used the latest jitter-analysis software options from both companies.
The testsIn each of the tests, the LeCroy Wavemaster 8600A scope performed more measurements in a fixed amount of time than either of the Tektronix scopes. For example, LeCroy's scope performed math calculations—a test that LeCroy proposed—twice as fast as the Tek TDS6604. When building an eye diagram from a 2.5-Gbits/s data stream, the LeCroy Wavemaster, with the SDM option disabled, acquired 6.5 times as much data as the TDS6604. To satisfy our own curiosity, we also performed a test with the SDM option enabled: The LeCroy scope outperformed the Tek scope by a whopping 651:1 performance ratio.
The tests also revealed a difference in the jitter measurements on a 622-Mbits/s data stream. The scopes produced drastically different results for deterministic jitter and random jitter, although total jitter was approximately equal. Without another piece of equipment such as a bit-error-rate tester (BERT) or a jitter analyzer, we couldn't determine which scope, if either, was correct.
Two days after the shoot-out, Agilent Technologies entered the 6-GHz real-time scope market when it announced the 54855A Infiniium scope. But the timing of the release didn't permit Agilent to participate in the shoot-out.
| Proposed by LeCroy | Proposed by Tektronix |
| •Amplitude and rms measurements on a 5.2-GHz sine wave, taken over a period of 60 s. | •Differential rise-time measurements with scopes in single-shot mode. |
| •Period and frequency measurements on a 5.2-GHz sine wave, taken over a period of 60 s. | •Build an eye diagram on a 2.5-Gbits/s PRBS7 (127-bit) serial data stream for 60 s (LeCroy SDM option turned off). At LeCroy's request, we repeated this test with LeCroy's SDM option turned on. |
| •FFT measurement on 5.2-GHz sine wave. | |
| •Math calculations such as computing squares of signals and summing them. | •Time interval error (jitter) measurement on a 622-Mbits/s serial data stream. |
| Makers of 6-GHz DSOs | ||
| Agilent Technologies Palo Alto, CA 800-452-4844; www.tm.agilent.com |
LeCroy Chestnut Ridge, NY 800-553-2769; www.lecroy.com |
Tektronix Beaverton, OR 800-426-2200; www.tektronix.com |
| Author Information |
| Martin Rowe has a BSEE from Worcester Polytechnic Institute and an MBA from Bentley College. Before joining T&MW in 1992, he worked for 12 years as a design engineer for manufacturers of semiconductor process equipment and as an applications engineer for manufacturers of measurement and control equipment. E-mail: m.rowe@tmworld.com. |
