Since writing the first post on this blog about the 741 op amp I’ve managed to get my hands on a few more 741s to dissect. Three of these I bought new, and two more I found back in some forgotten corner of my lab.
First up, a brand new National/TI LM741. Although National Semiconductor was acquired by TI in 2011 and they stopped using the National brand soon after, the LM741 that you can buy in 2020 still has the National logo on it. I can’t figure out why though, because changing the logo on the package is as simple as reprogramming a printer (which happens anyway because it needs to print a new date code every week or month).
The 741 is easily the most iconic opamp ever made. Designed by Dave Fullagar at Fairchild as a user-friendly, general-purpose op amp, it became a huge hit with electronic designers. Billions have been produced since its introduction in 1968, by a wide variety of manufacturers. What’s perhaps even more amazing is that it’s still being produced today by TI and ST, despite being hopelessly out of date. Fifty years of development has produced a wide array of opamps that are faster, more accurate, less noisy and less power-hungry than the 741. Yet somehow, this classic part keeps hanging on, basically unchanged for over half a century.
Today we’ll have a look at the insides of a couple of different 741 chips. Although it is entirely possible for manufacturers to just copy the exact layout, especially for something as old and simple as this, it turns out that each company actually makes its own unique design.
National Semiconductor LM741CN
National has been manufacturing this device for ages, as part of their LM (Linear Monolithic) range of analog ICs. Even after National’s acquisition by TI in 2011, it has remained in production alongside TI’s own uA741.
The layout is very compact; the total die size is only 1100 by 800 microns. Some test structures are visible along the lower edge. The ID on the right edge of the die says “LM741U” and “UK”, the latter probably referring to National’s fabrication plant in Greenock. Some of the PNP transistors have circular emitters; this improves their matching properties and increases their breakdown voltage.