in product marketing for telecom and datacom products. The of and JAN/ FE B 20 13 4 ® HIROSHI GOTO is Anritsu Co. ’ s business development manager for general purpose test equipment. He has more than 25 years of experience in communications. He began his career in design engineering of optical products and has spent the past 10 years By HIROSHI GOTO Is your problem rooted in your high- speed technology design or in the equipment you’re using to test it? T HE IMPORTANCE OF testsignal fidelity grows as data rates increase. That’s because waveform inadequacies cause one of two business problems: One, they make component flaws seem worse than they really are and increase costs by forcing unnecessary redesigns; two, and more troublesome, they may conceal flaws and allow products with performance deficiencies to be shipped. Bit- error- rate testers ( BERTs) such as the one shown in Figure 1 cast the final judgment of component and system performance – BER – making the selection of the proper BERT imperative to successful design and production of high- speed devices and systems. Evaluating channels and receivers begins with the test waveform. For accurate compliance and useful diagnostic testing, pattern generators must have sufficient bandwidth to excite at least three harmonics. Figure 2 shows an instrument- grade eye diagram that has smooth, continuous edges with no harmonic distortion, bandwidth limiting, overshoot, or ringing, even at 25 Gbps. BERTs that produce such eye diagrams can support all three harmonics. Test waveforms free of ISI and DCD To achieve eye diagrams like the one shown in Figure 2, test waveforms must have minimal inter- symbol interference ( ISI) and duty- cycle distortion ( DCD). ISI, the dominant signal impairment at high data rates, is caused by the frequency response of the channel. It gets its name because the frequency content associated with a given symbol depends on the values of neighboring symbols. Long strings challenges high- speed technology test measurement