Real-time DSO bandwidth jumps to 15 GHz
By Dan Strassberg -- EDN, February 17, 2005
Tektronix has announced what it calls the world’s fastest, most-capable, real-time oscilloscopes and a new probe intended to simplify connecting to such ultra-high-speed serial buses as second-generation PCI-Express, SATAIII (serial advanced-technology attachment), and double XAUI (10-Gbps attachment-unit interface). According to Thomas Berghall, Tek’s worldwide marketing manager for Performance Scopes, Accessories, and Solutions, “These emerging standards push data rates beyond 4 Gbps, requiring real-time-scope bandwidths in excess of 10 GHz.” Several months ago, Agilent Technologies (www.agilent.com) became the first supplier to respond to this requirement when it announced greater-than-10-GHz real-time scopes that exceeded Tek’s then-industry-leading 8-GHz bandwidth.
The new members of Tek’s TDS6000 DSO (digital-storage-oscilloscope) family are the $125,000, 15-GHz-bandwidth, four-channel TDS6154C, which can measure 30-psec 20 to 80% rise times with an error that is typically less than 5%, and the $100,000, 12-GHz, four-channel TDS6124C, which users can upgrade to a TDS6154C. The probe is the $10,000 P7313 Z-Active, low-loading, differential unit (Picture).
A key to the increased bandwidth is third generation SiGe (silicon-germanium) IC technology. Tektronix collaborated with IBM Corp (www.ibm.com) to develop several SiGe ICs used in the new products. Says Berghall, “The SiGe technology deserves part of the credit for the new scopes’ unprecedented timebase stability—which makes possible extremely accurate jitter measurements.”
Like Agilent’s faster-than-10-GHz units, the new Tek scopes use ADCs whose maximum real-time sampling rate is 20G samples/sec. The scopes must thus interleave the ADCs from two channels to sample beyond the Nyquist frequency of signals that contain components higher than 10 GHz. Therefore, when sampling in real time, the scopes can deliver their full bandwidth only when no more than two channels are active. Unlike the Agilent units, however, the new TDS6000 scopes allow using the maximum two-channel-mode memory depth of 64M samples per active channel at the highest sampling rate (40G samples/sec), enabling the capture of full-bandwidth records as long as 1.6 msec.
The TDS6124C provides 12-GHz analog bandwidth and user-selectable DSP for channel-to-channel and unit-to-unit matching. In addition to the DSP functions found in the TDS6124C, the TDS6154C includes DSP-based bandwidth extension to 15 GHz, which linearizes the phase response and adjusts the magnitude response throughout the scope’s bandwidth.
According to Tek, the P7313 probe’s SiGe Z-active architecture offers typical greater-than-12.5-GHz true bandwidth, high dc impedance, 20-to-80% rise time of 25 psec, and the stable high-frequency loading of Z0 probes. These features combine to provide high bandwidth, flat frequency response, low-loading, and low-noise differential inputs. Detachable Tip-Clip assemblies make it possible to replace a tip for a fraction of the cost formerly associated with such hardware changes. Moreover, the Tip-Clip assemblies are interchangeable depending on connectivity needs, providing a large degree of flexibility in using the probe.
Tektronix Inc, 1-800-426-2200, www.tektronix.com.
