A while ago, I found this little PCB in my junk pile:
It came out of an old webcam that I used on my PC back in the early 2000’s. Although I didn’t keep any pictures of the webcam itself, I recall that it was a Logitech Quickcam Messenger, a cheap USB camera meant to be used with MSN Messenger and other instant messenging programs. I remember using it for that purpose a few times, but once the novelty wore off it just ended up gathering dust in a corner somewhere.
From 1986 to 2008, HP sold a line of workstations and servers powered by a processor line called Precision Architecture, or PA-RISC. These systems were mainly targeted at professional users in industry and academia, and provided high performance at very high cost. Nevertheless, like all computers they became obsolete after just a few years, and I managed to find a heap of old HP equipment in the recycling bin of the local university. Today we’ll have a look at the PA7100 CPU and its accompanying “Viper” memory/IO controller (MIOC), both made in the early ’90s.
Here we see both chips side by side. The CPU has HP part number 1FT9-0002, although according to the sticker on the left it used to be 1FT9-0006. Not sure what’s going on here… In any case, it’s housed in a large ceramic PGA package with capacitors on top and a screw terminal to attach a heat sink.
The Viper has part number 1FZ6-0006. Its package is similar to the main CPU’s, but slightly larger and with fewer pins.
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 What’s perhaps even more amazing is that it’s still being produced today by TI and ST, despite being hopelessly out of date.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.