Inside an Op Amp with Interesting “butterfly” Transistors #ReverseEngineering
Some great silicon detective work on Ken Shirriff’s blog on looking at the silicon die of a quad operational amplifier (Op Amp) chip.
The chip above has a design that look kind of like butterflies. These patterns are special JFET input transistors that improved the chip’s performance. This chip is a Texas Instruments TL084 quad op amp and the symmetry of the four op amps is visible in the photo. (You can also see four big irregular rectangular regions; these are capacitors to stabilize the op amps.) In his article, Ken describes these components and the other circuitry in the chip and explain how it works. The article also includes an interactive chip explorer that shows each schematic component on the die and explains what it does.
The blog post is very detailed on electrical operation, component layout and use, and how he photographed the chip.
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