High Bandwidth Real Time Oscilloscopes

Today's high end real time oscilloscopes are a lot more like EDA tools running on powerful PCs than simple measurement devices. They contain an Intel type computer and run the Windows operating system. They can connect to an Ethernet network and be remotely controlled or viewed from anywhere in the world through the internet. In addition to the computer side, they have sophisticated data acquisition electronics front ends to actually make the voltage vs. time measurements. The application software running on them allows sophisticated data processing of the measurements. The high bandwidth real time oscilloscope that I helped choose for my company is the SDA6020 made by Lecroy. This scope should be useful for signaling rates up to 3.125 Gbps. Some important specifications of the model that I use are:

Lecroy SDA6020 Oscilloscope
4 Channels
Bandwidth = 6 GHz
Rise Time = 75 ps
Sampling Rate = 20 GS/s all channels
Memory Depth = 32 MS/ch all channels at full sampling rate

Just as important as the oscilloscope are the probes. The probes that I use are HFP3500 single ended, D600A-AT differential browser tip, and D600ST-SI differential solder in. The differential probe tips are used with the WL600 WaveLink differential probe body. The specs for these probes are listed as follows.

D600A-AT
bandwidth = 6 GHz
rise time = 70 ps
input resistance = 4 KOhm differential (2 KOhm either end to ground)
input capacitance = Not directly spec'd (differential input resistance is down to about 200 Ohms at 6 GHz)
dyanmic range = +/- 2.4 V

D600ST-SI
bandwidth = 6 GHz
rise time = 65 ps
input resistance = 4 KOhm differential (2 KOhm either end to ground)
input capacitance = Not directly spec'd (differential input resistance is down to about 250 Ohms at 6 GHz)
dynamic range = +/- 2.4 V

HFP3500
bandwidth = 3.5 GHz
input resistance = 100 KOhm
input capacitance = 0.7 pF
dynamic range = +/- 4 V

SDA6020 Features

Some really nice features about this oscilloscope are:

• Jitter measurements
• Extrapolated to low probabilities of occurence
• Extract random and deterministic components of jitter
• Serial data measurements
• Eye diagrams and mask testing
• Allows automatic zooming to mask violations
  
• Bit error rate testing (very basic)
• Automatic deskew fixture (TF-DSQ) for deskewing channels
• Can make setup and hold measurements for all data and clock edges in a large capture
• For all measurements, can display statistics, histograms, and a track plot of the measurement on the measured waveform
• Connection to Matlab, Mathcad, or Excel for additional processing

In addition to the capabilities, the scope is very fast at doing this processing. With up to 4 MS/s sampling the scope is very quick and responsive when doing complicated measurements and waveform processing. When set to 32 MS/s sampling rate, there can be several seconds delay in between triggers while the scope does the processing.

With any windows based software, these modern scopes are not as stable as most engineers are used to with older oscilloscopes. It is not uncommon for the scope to crash and require a reboot. Also, there are many bugs in the application software that you need to be aware of. The vendors provide software updates on their web pages and fix the bugs as they are found, just like an EDA tool company! It is a good idea to keep up to date on the software patches.

Overall I really enjoy using this scope and it has made my job much easier. Great tools and toys like this keep engineers happy! List price on a setup like this is well over $100 K, so happiness does not come cheap!

Looking Forward

Lecroy now has available an 11 GHz real time oscilloscope with 40 GS/s sampling rate. Tektronix now has available an 15 GHz real time oscilloscope with 40 GS/s sampling rate. For high data rate serial systems, there are other test equipment options available such as the BERTSCOPE from Synthesys Research and a Time Interval Analyzer from Wavecrest. It is currently not clear to me if a higher bandwidth real time oscilloscope or one of these other options will be better for the next generation of data rates.