Inside the die of Intel's 8087 coprocessor chip

Looking inside the Intel 8087, an early floating point chip, I noticed an interesting feature on the die: the substrate bias generation circuit. In this articleI explain how this circuit is implemented, using analog and digital circuitry to create a negative voltage.Intel introduced the 8087 chip in 1980 to improve floating-point performance on 8086/8088 computers such as the original IBM PC. Since early microprocessors were designed to operate on integers, arithmetic on floating point numbers was slow, and transcendental operations such as trig or logarithms were even worse. But the 8087 co-processor greatly improved floating point speed, up to 100 times faster. The 8087's architecture became part of later Intel processors, and the 8087's instructions are still a part of today's x86 desktop computers.

A detailed and very technical article.