The Invisible Problem
Written by John Teel.
The numbers didn’t make sense.
My circuit was consuming too much current, and I had no idea why.
Current consumption was a critical spec, and my design was failing.
I had already run hundreds of simulations, and none of them showed this excess power consumption.
Not even close. Yet here it was, happening in the real world—mocking me.
And at the time I was working as a microchip designer at Texas Instruments, in the power management design group, where power efficiency was everything.
So, I did what any determined engineer would do…
…I went into the lab and started hunting for the problem.
And as the days dragged into weeks without answers, management started breathing down my neck.
The project was slipping behind schedule.
But, like any debugging effort, there was no way to estimate when I’d have a solution—because I didn’t even know what the problem was yet.
That’s the thing about debugging. It’s always the hardest part to forecast.
You can pretty accurately predict how long it will take to design a circuit or layout a PCB.
But when you’re dealing with an unknown problem with an unknown cause and an unknown solution, the only thing you can do is to keep searching.
Tracking down where the current is going is always a challenge.
Unlike voltage, which you can measure across two points, current has to be measured inside the circuit—you have to physically break the connection and insert a meter.
And when you’re working with a tiny integrated circuit, it’s exceptionally harder.
For weeks, I sat hunched over a probe station, carefully maneuvering microscopic probes onto different parts of the circuit to try and isolate the source of the leakage.
When that wasn’t enough, I took a more aggressive approach—I started cutting out sections of the circuit with a laser, trying to isolate the problem one piece at a time.
Finally, after all this effort, I managed to isolate the exact part of the circuit where the extra current was flowing.
But I was still missing two things: an explanation and a solution.
Nothing in the schematic could explain this current leak.
That’s when it hit me. I was looking in the wrong place.
The schematic is just a conceptual approximation of the real world, but a microchip isn’t just a collection of ideal transistors and resistors.
It’s a physical structure, built from layers of silicon, metals, and insulators. And sometimes, that physical structure creates things you never intended to exist.
When I shifted my focus from the schematic to the physical layout, I finally found the culprit:
A parasitic transistor had been created and was turning on and draining away current.
This transistor wasn’t in the design—at least not intentionally. But in semiconductor design, parasitic devices can form unintentionally when different components interact in ways you don’t expect.
In this case, some of the nearby components had formed a transistor out of thin air—a ghost in the silicon. And it was leaking precious current.
The fix? Better isolation. I adjusted the layout so that certain parts of the circuit couldn’t unintentionally form transistors with their neighbors.
Once I made that change, the extra current disappeared.
This experience changed the way I approach design.
It taught me that a schematic is only an approximation of the real world.
Whether you’re designing a microchip or a PCB, the real circuit isn’t just what you see in your schematic design software—it’s how it physically exists in the real world.
Parasitics, unintended interactions, real-world tolerances—these are things no schematic can fully capture.
If you ever find yourself chasing a problem that “shouldn’t exist,” step back and ask yourself:
Am I only looking at the schematic? Or am I looking at the real-world circuit?
Because the real world doesn’t care what’s in your schematic.
In product development, the biggest issues are often the ones you can’t see—especially the first time around.
That’s exactly why I created the Hardware Academy—to help you navigate the hidden problems no schematic or tutorial can prepare you for, and to guide you through every step of developing and launching a successful electronic product.
