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标题: 示波器模拟带宽超过60GHz [打印本页]

作者: stupid 时间: 2012-5-9 13:58
标题: 示波器模拟带宽超过60GHz
On April 24, only 13 days after Agilent Technologies had announced the availability of 63-GHz bandwidth (–3-dB- bandwidth) in its Infiniium 90000Q RT DSO (real-time sampling digital-storage-oscilloscope) line, LeCroy revealed that its 10Zi series of LabMaster modular DSO systems would henceforth offer a 65-GHz bandwidth acquisition module. A mere two months earlier, LeCroy had brought forth the 10Zi line with an industry-leading maximum bandwidth of only 60 GHz.

The company ascribed its ability to offer the even-higher bandwidth to better-than-expected performance of the proprietary Si-Ge (Silicon-Germanium) ICs on which the 10Zi’s operation depends. Perhaps even more significantly, LeCroy accompanied its announcement of the increased bandwidth with the news that it is working toward offering a 100-GHz bandwidth LabMaster acquisition module in 2013.

A 100-GHz LabMaster would not be LeCroy’s first scope to achieve such bandwidth. It would, however, be its first (and presumably the industry’s first) real-time DSO with such bandwidth. Approximately five years ago, LeCroy introduced the WaveExpert sequential-sampling-scope system, which offers 100-GHz bandwidth—but only for repetitive (albeit not necessarily periodic) signals.

In addition to what had been the only DSO bandwidths greater than 33 GHz, sequential-sampling instruments allow very high vertical resolution—typically 14 bits nominal, whereas ultrawideband RT DSOs generally offer only eight bits nominal. Because sequential-sampling DSOs usually require a new iteration of the input waveform for each data point they capture, however, measurements often take more than 1000 times as long as equivalent measurements with RT DSOs. The torpid pace of waveform acquisition therefore frequently frustrates signal-integrity engineers and electro-optical-communications-system designers who, until recently, had no alternative to the sequential-sampling instruments.

LeCroy may believe that it can get a 100-GHz RT DSO to market in less than 20 months because of its use of a proprietary frequency-domain-based architecture called DBI (digital bandwidth interleaving.) The company’s two major competitors, Agilent and Tektronix, have historically relied upon a technology that can be called TDI (time-domain interleaving) or pipelining of ADCs. On paper, TDI is more straightforward than DBI, but implementing TDI in a system that must acquire a new sample approximately every 4 ps is anything but straightforward.

The beauty of DBI is that it divides a broadband signal into multiple frequency bands before simultaneously converting all bands from analog to digital and then merging the several streams into a single stream whose data rate is equal to the sum of the rates of the individual streams. The 65-GHz system uses two streams, each working with signals whose bandwidth is approximately 32.5 GHz—half of the input signal’s 65-GHz-bandwidth. One signal is at baseband from the outset; the other is translated down to baseband before analog-to-digital conversion. Each ADC converts at a rate of 80 Gsamples/s so there is no aliasing. The processes that merge the streams are not intuitive, but they result in a stream that, for the 65-GHz system, is indistinguishable from the stream you would create with pipelined converters operating at a combined rate of 160 Gsamples/s (see bit.ly/J9fMTK for LeCroy’s explanation of the DBI process).

Extending the bandwidth to 100 GHz requires three streams, each with approximately the same bandwidth as that of each of the 65-GHz system’s two streams. The effective conversion rate for the 100-GHz system is thus 240 Gsamples/s. An advantage of some three-stream DBI systems is that, without interleaving, the hardware modularity is based on four-channel groups. Three of those channels join to produce one maximum-bandwidth (in this case, 100-GHz) channel. Sometimes, it is possible to provide user access to the fourth channel, which, in this case, could process signals having 36 GHz bandwidth.

LeCroy says that it is still too early to predict whether its 100-GHz system will offer users a 36-GHz channel side-by-side with each 100-GHz channel, but because the LabMaster system accommodates as many as 20 acquisition modules, the company expects to be able to offer systems that users can configure for eighty 36-GHz channels, forty 65-GHz channels, or twenty 100-GHz channels. Such high channel counts are especially useful in work on multilane optical-communications systems.

The US price of the LabMaster 10-65 Acquisition Module (65 GHz on two channels, 36 GHz on four) is $355,000; that of the LabMaster 10-60 Acquisition Module (60 GHz on two channels, 36 GHz on four) is $315,000; and that of the LabMaster MCM-Zi Master Control Module is $96,900. A working system requires one MCM and at least one acquisition module.

Meanwhile, at our request, Tektronix, the company long regarded as the largest manufacturer of scopes, released the following statement regarding its position in the competition for the hearts, minds, and purchase orders of high-end real-time scope users:

"The bandwidth wars among scope vendors will probably always be a reoccurring theme and while bandwidth can be important we see even more value in ensuring we are exceeding customer expectations through performance and innovation beyond just banner specs. Overwhelmingly our customers are telling us the key is to provide the right solutions for their specific applications. Customers doing high-speed serial designs not only need compliance-test support but, more importantly, they will need to debug their designs when they fail a compliance test, therefore, it's important that customers have a complete debug solution as part of their testing toolset. To serve that need we offer the best Serial-Bus Debugging toolset for high-speed serial debug, including our DPOJET measurement and analysis suite and our unique Performance MSOs. We keep a very close pulse on what customers need in order to have the right products available at the right time. While we currently offer 33-GHz performance to our customers, should they need faster high-speed support today, we have our sampling oscilloscopes which offer the best noise performance at a much lower price point than the recently announced real-time scopes from our competitors."—Brian Reich, General Manager, Performance Oscilloscopes, Tektronix

作者: covigs 时间: 2013-1-17 15:47
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