[Editor's note : this is the next entry in a series on oscilloscope specifications and selection by this author; you can see a linked list of previous entries immediately above the "About the author" section.]
The emergence of faster processors and new custom ASICs on oscilloscopes has resulted in oscilloscopes that now advertise waveform updates rates of up to one-million-updates per second. In fact, the recent trend is for update rate to become a leading oscilloscope specification, almost becoming more important than memory depth.
While one-million-waveforms per second is impressive, it is important to understand what the specification really means, as well as the settings required to achieve an ultra-fast update rate such as this. An oscilloscope that runs at 300,000 waveforms per second in one mode may run at less than one waveform per second in another mode.
As a user, it is important to know how the oscilloscope will ultimately be used. Will the oscilloscope simply capture data or do margin testing via masks? Will the oscilloscope be used as a deep analytical tool separating jitter or doing real time eye measurements? Will the oscilloscope's data be offloaded to a PC for further analysis or will everything be done inside the oscilloscope's hardware?
It is questions like these that matter when update rate is used as a serious criterion for purchasing an oscilloscope. When purchasing an oscilloscope, do not just believe the data sheets. To make an informed decision, understand how the oscilloscope will be used and measure the update rate based on this. In other words, do not purchase an oscilloscope based off a one million waveforms per second specification when in your use model, the oscilloscope is updating at less than one update per second.
This article, which is presented as a pdf, looks at these issues:
•What is update rate?
•How to measure update rate
•Where the limitations begin