Making an ASIC—The Secret of Building a Good, Cheap Oscilloscope (.PDF Download)

Here at Keysight Oscilloscope HQ, we talk a lot about ASICs (application-specific integrated circuits). But why? Who cares about the internal architecture of a cheap oscilloscope? All that matters is how well it works, right?  We agree. That’s why we design and use custom oscilloscope-specific chips.

How, though? It’s not like custom ASICs just appear out of thin air; it takes years of meticulous planning and R&D effort. We develop ASICs for three main reasons: performance, reliability, and cost. Let’s take a quick look at the performance aspect, and then a longer look at how an ASIC is made.

Performance

This is usually the driving motivation for creating our own ASIC.  We like to use off-the-shelf components when we can, but often it’s not possible. For example, our research-grade Infiniium Z-Series oscilloscopes have a sample rate of up to 160 Gsamples/s. Good luck finding an off-the-shelf 160-Gsample/s analog-to-digital converter (ADC). Even if you could locate one, it probably wouldn’t meet the stringent noise spec requirements for oscilloscope use. So, we make it ourselves. If you find yourself in a similar situation and don’t happen to have an ASIC design team like we do, most of it can be contracted out to third parties.

Then, what happens once you have the world’s fastest ADC?  How do you handle all of that data?  An oscilloscope must save, plot, measure, and process that data in near real-time. You could offload it into a processor or FPGA (which we do for some things), but to get data analyzed the way we need at the speed we need, we opt for a digital ASIC.

The Making of an ASIC

Several different steps are involved in the creation of an ASIC.  Before any chip starts development, there must be a long-term product plan—what do designers want to have five or 10 years down the road? Products in the future will need new features or capabilities that will sometimes warrant an ASIC (Fig. 1).