Speed Demon: The latest Tektronix
real-time oscilloscopes offer bandwidths of 12 and 15 GHz, sufficient to
acquire and analyze the most demanding serial-communication
Two real-time oscilloscopes from Tektronix offer engineers the high
bandwidths to test and characterize new serial data links that continue to
supplant parallel-shared data buses in computer, communication, and consumer
electronics. These serial links include PCI Express, Serial Advanced Technology
Attachment (SATA), and 10-Gbit Attachment Unit Interface (XAUI). PCI Express,
for example, carries a 300-fold increase in data compared with its PCI-bus
forerunner. The new scopes offer bandwidths of 12 GHz (TDS6124C) or 15 GHz
(TDS6154C). Both scopes use custom front-end SiGe ICs that operate at 40
Gsamples/sec for one active channel, or 20 Gsamples/sec for four-channel
Because serial communications produce square waves, engineers must capture the third or fifth harmonic of a signal's clock frequency to represent the signal accurately. Thus, the 15-GHz-bandwidth TSD6154C will capture a 10-Gbit/sec fiber-optic channel with a 5-GHz clock out to its third harmonic. Moreover, it can acquire the fifth harmonic of a 3-GHz clock signal used with SATA-III signals. To put the scope's performance another way, it can measure the rise time of a 40-ps signal with about 3 percent accuracy, and the rise time of a 30-ps signal with an accuracy of about 5 percent.
Digital signal-processing technology in each scope enhances its magnitude and phase response over the entire bandwidth. The TDS6154C also employs signal processing to extend its bandwidth to 15 GHz. Users can turn the signal-processing hardware on or off.
In addition to operating at high bandwidths, the two new scopes offer standard record lengths of 4 Msamples/channel for one- or two-channel operation, or 2 Msamples/channel for four-channel operation. An option expands the record length to 64 Msamples/channel for applications that require lengthy data capture. The longer record length translates to a 1.6-msec capture period at the highest sampling rate. That period gathers more than enough data with which engineers can characterize almost all serial-communication waveforms.
Scopes cannot do much without trigger selections, and the Tektronix instruments delivers over 1,400 triggering combinations. Users can select edge, glitch, width, runt, pattern, and other characteristics that depend on one event or on sequential events from two channels. A serial-pattern trigger mode compares 40-bit sequences at up to 3.125 Gbit/sec.
Engineers can use the new scopes to decode high-speed 8b/10b serial signals and correlate events across physical (signal) and link (traffic) communication layers. A scope's information can appear in several user-selected formats that present waveforms, eye diagrams, characters, words, and data such as jitter statistics and histograms. Optional processing software reports on acquired data as it relates to PCI Express, SATA, Infiniband, XAUI, and other standards.
Tektronix complements its new scopes with the P7313
differential probe that features a flat step response and a high impedance. The
bandwidth reaches 12.5 GHz when the probe operates with a TDS6154C scope. To
enhance probing, the P7313 comes with a kit of "Tip Clip" accessories that
include solder-in probe tips as well as handheld probe tips for use on circuit
boards. An external fixture also can hold a probe in place.