ASSET InterTech published a white paper titled: Bandwidth tests reveal shrinking eye diagrams and signal integrity problems. The paper explains how increasing bus speeds on circuit boards could create havoc for signal integrity on those buses, in turn degrading the bus’ throughput performance. Each new generation of a high-speed bus typically runs at a higher signal frequency, but this decreases the margin for error on the bus, making it more sensitive to disruptions from jitter, inter-symbol interference (ISI), crosstalk and other factors.
According to the ebook, to avoid potential problems on high-speed buses like DDR3, PCI Express, Intel QPI, Serial ATA, USB and others, bus performance must be validated during each phase of a system’s life cycle, including design/development, manufacturing and as an installed system in the field. Unfortunately, effectively and economically validating the signal integrity on a high-speed bus has become more difficult as the limitations of legacy probe-based test equipment such as oscilloscopes have become more obvious in recent years. Now though, non-intrusive software-driven test methods based on embedded instrumentation are providing alternative validation solutions that are more cost-effective and deliver observed signal integrity data.
Bandwidth tests reveal shrinking eye diagrams and signal integrity problems
An old story compares the electronics industry’s unprecedented achievements with the automotive industry. If cars had kept pace with Silicon Valley, we could buy a vehicle with a V32 engine and capable of 10,000 mph; or a 30 pound car that gets 1,000 miles to the gallon — either one at a sticker price of less than $50!
The high-speed serdes and memory buses in today’s systems are a lot like that V32, 10,000 mph car screaming down a crowded highway with thousands of other cars. There’s not much margin for error at 10,000 mph. What if a car or a bit on a high-speed bus is going too fast? Or another is too slow? Or the one in the next lane is swerving into the wrong lane? They crash. On a high-speed bus it’s jitter, intersymbol interference (ISI) and crosstalk. And as the speed of a bus increases, the margin for error decreases and disruptions in traffic increase.