Agilent - When is it Time to Transition to a Higher Bandwidth Oscilloscope?

Our thanks to Agilent for allowing us to reprint the following article.

When purchasing an oscilloscope to test new designs, the primary performance specification that most engineers consider first is the scope's bandwidth. Another key consideration is always price. Unfortunately, there is a fairly linear relationship between these two characteristics of a scope; bandwidth and price. Since most of us must work within constrained capital equipment budgets, engineers tend to purchase test equipment that has just enough performance to meet their current needs. But with each new design-start, performance requirements often increase in order to stay competitive and to deliver newer, faster, and more feature-rich smart products that customers demand. So how do we determine how much bandwidth is required for today's projects, and when do we know when it is time to "move up"?

Although many of today's embedded designs are mixedsignal in nature (contain both analog and digital signals), it is usually the maximum speed of the digital signals (clock rate and edge transition times) within a design's central processing unit (CPU) system that determines how much oscilloscope bandwidth is required. And it is often the timing specifications of CPU memory that must be considered. The most common type of memory used in most of today's embedded designs is double data rate (DDR) memory. This type of memory clocks data into and out of memory on both the rising and falling edges of the clock signal.

Let's assume that in your last design project the CPU system in your embedded design was based around DDR1 memory technology with data transfer rates in 200 Mbps range. And if you used a 500-MHz bandwidth scope to capture and verify critical timing parameters of your CPU system running at this speed, this scope probably provided you with sufficient measurement accuracy. But now your next design will be based on higher speed DDR2 technology. Will you need to purchase a higher bandwidth scope? And how much bandwidth will be required?...

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