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10 DESIGN007 MAGAZINE I FEBRUARY 2023 What happens when die sizes shrink? As IPC design instructor Kris Moyer explains, quite a bit. Shrinking silicon can mean rising sig- nal speed and rise times, and traditional PCB designers may find themselves dealing with problems formerly only seen by RF engineers. We asked Kris to discuss the pros and cons of silicon shrinkage and some of the techniques and trade-offs that PCB designers and design engineers need to understand as they find themselves entering the RF arena. Andy Shaughnessy: is issue focuses on the effects of shrinking silicon on a board's signal integrity and EMI. So, what do PCB designers need to understand about die shrinkage? Kris Moyer: Basically, the main thing that hap- pens when you shrink the size of the die is that it shrinks the length of the channel of the tran- sistors inside the die. What that effectively does is it increases the speed of the circuit, meaning it decreases the rise time or the fall time. en you end up having to start treating your traces, geometries, and transmission lines almost as if they're RF designs. We've heard for decades that RF designs are their own special little area of black magic, because we start dealing with all these waves and fields and so on. We say in digital design that it's the rise time and not the frequency. Which is the driving force, the key factor, that causes the need for all these high-speed designs? What is the frequency content? Fourier's theorem says any wave form— square wave, triangle wave, sawtooth wave, or any wave form—can be recreated as a super- position of a sufficient amount of sine waves and cosine waves of sufficiently higher har- monics. Let's take a fundamental frequency, 1 kilohertz. And you have A1, A3, A5 and A10 kilohertz. You have all these harmonics, we Feature Interview by the I-Connect007 Editorial Team

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