Ken Shirriff Reverse Engineers Nintendo's Game Boy Color Audio Amp — From a Die Shot
With a high-resolution die shot of a decapped chip, Shirriff walks through identifying components and creating a schematic for the part.
Vintage computing enthusiast and reverse engineer Ken Shirriff has worked to figure out the inner workings of the audio amplifier used in Nintendo's Game Boy Color handheld console — from an image of the decapped die.
"The Nintendo Game Boy Color is a handheld game console that was released in 1998," Shirriff writes. "It uses an audio amplifier chip to drive the internal speaker or stereo headphones. In this blog post, I reverse engineer this chip from die photos and explain how it works. It's essentially three power op-amps with some interesting circuitry inside.
"This amplifier chip from 1998 has about 100 transistors and is simple enough that the circuitry can be traced out under a microscope. (In comparison, a Pentium II processor from the same time had 7.5 million transistors.) The chip illustrates important analogue design functions such as the differential pair and current mirror, and how they can be combined to build an amplifier.
"People have reverse engineered many Nintendo chips to help build Nintendo emulators," Shirriff notes. "I don't think knowing the audio chip circuitry helps with emulation, but it's interesting to see how it is constructed."
Shirriff's blog post has a second purpose, too: Demonstrating how he recognises certain components, like NPN and PNP transistors, resistors, and capacitors with nothing but a two-dimensional though high-resolution image of the silicon die to go on. Shirriff also identifies two common subcircuits, often found in other analogue designs: A current mirror and a differential pair.
Shirriff's full write-up is available on his blog.