Tektronix aims at DDR3 with upgraded scope family

Tektronix has increased the sampling rate and bandwidth on its latest generation of mixed-signal oscilloscopes (MSOs) to deal with the move by system designers to adopt memories that use the DDR3 protocol.

Trevor Smith, market development manager for Tektronix, said the clocking scheme for DDR3 is significantly different to the technique used for older DDR2 memories. Instead of being laid out in a simpler but more capacitance-prone tree structure, DDR3 relies on a bus structure that allows for each chip receiving the clock at a different time to its neighbours.

“If you have the memories on a DIMM, for example, the memory controller issues the clock signal that travels down the DIMM, reaching each chip successively,” Smith explained. “So, the signal is skewed in time based on how fast the wavefront travels down the board. There may be about 20mm between each chip. In an FR4 PCB material you are looking at a delay of about 60ps for each one.

“You can get much better signal integrity at high speeds than with DDR2 but you have to consider the skew that has been deliberately injected. If you are trying to debug and understand what is going on on the flyby clock you need some extremely high-performance channels.”

To be able to resolve that kind of delay, Tektronix upped the performance of the analogue-sampling channels on its MSO70000 to a bandwidth of 20GHz and a peak sampling rate of 50GHz. The 16 digital channels, which can be used to probe the data lines, sample at up to 12.5Gb/s. The cycle time for the DDR3 data lines is around 800ps, so these channels provide the resolution needed to monitor those, Smith claimed.

Smith said the larger number of acquisition channels on an MSO are better for DDR3 debugging than conventional scopes. The MSO7000 lets users switch probe ports between the four analogue sampling and 16 lower-resolution digital capture inputs dynamically.

“What you can do is connect the digital channels to the parallel bus and then, if you spot something that isn’t quite right you can flick a switch on the front and route that digital channel through one of the analogue inputs to see what you have,” said Smith.

Although the introduction of DD3 provides the opportunity for Tektronix to sell a new crop of DSOs, the company sees other applications for the range in the latest HDMI digital video standard and among FPGA users who are getting to grips with the 10Gb/s serial interfaces that the latest devices offer. “And you want to correlate what is happening on there with the low-speed information that is turning the bus on and off,” said Smith.

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