We often think of analog computing as a relic of the past, room-sized monstrosities filled with vacuum tubes doing their best to calculate Monte Carlo simulations or orbital velocities. Analog isn’t as dead as it might seem though, and analog mix signal design engineer [Nanik Adnani] gave us a crash course on analog circuits at Supercon 2024.
For those of us less familiar with analog circuits, [Adnani] helpfully offered a definition of analog circuit design as “the design of electronics that create or manipulate continuously variable signals.” It turns out, that even our nice, clean digital signals are actually more analog by the time they interact with the real world. This comes down to various factors like substrate losses, conductors, impedance, and even capacitance. Given the difference in scale between a logic gate and the actual pins the signal comes out of from an integrated circuit, it becomes clear that the amount of current the pin can handle versus the logic gate inside the chip is quite different. In order to bridge the gap, chips use a physical interface, or PHY, which happens to be an analog interface which allows the logic on the chip to communicate off the chip.
[Adnani] explained how every digital protocol in common usage requires some degree of analog circuits including LoRa, USB, CAN, etc. Most chips handling these protocols have a separate analog team designing the analog circuit which requires slightly different metal layer design, so while determining the exact function of an analog circuit can be difficult to determine from an X-ray of the chip, finding where they are compared to the digital compon ..
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