Zooming in at the top-left corner, we can clearly see the Threshold comparator. Also clearly visible are three very large NPN transistors: the two output transistors (Q22-Q24) on either side of the output pin, and the discharge transistor (Q14) next to its own bond pad. Note that the “555” numbers are sitting on top of the three 5 kOhm resistors R7-R8-R9 that span almost the entire width of the chip. The top left corner has a number of colourful test patters. On the right edge is a row of As showing that each mask is in its first revision. But there’s no manufacturer logo or other identifying information other than a barely visible “P152” between the VCC and GND pins. Inside we find three large 5s showing the chip’s function. Thomson (a French company) long ago merged with SGS of Italy to become STMicroelectronics, which is one of the largest semiconductor manufacturers today. Today I’ll show a couple of them, starting with the oldest one I found in my collection: a TDB0555DP by Thomson. ![]() Originally released by Signetics, it was quickly copied by most other semiconductor manufacturers of the day. It’s a rather clever setup with two dozen transistors forming two comparators, a flip-flop and an output driver. In Chapter 11, Camenzind shows the schematic of the original 555 timer: I highly recommend reading it (available on paper or as a free download) if you’re interested in analog IC design. ![]() There are many ICs that can generate square or triangle waves, but I can’t think of any chip that can function as a one-shot, a flip-flop, Schmitt trigger, or one of a million different oscillator types like the 555 can.ĭesigned by Hans Camenzind in 1972, its story is described in detail in Camenzind’s own book Designing Analog Chips. Quite unlike the 741, which established op amps as a common IC type, the 555 has remained largely in a class of its own. ![]() Released just three years after the 741, it similarly took the world by storm, selling billions of units over five decades. If there’s a classic analog chip even more iconic than the 741 op amp, it has to be the 555 timer.
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