I bought this smoke and carbon monoxide detector several years ago, and it’s been doing its job just fine ever since: mostly being silent, screaming when I burn my toast, and beeping every two years or so when its batteries run out. Recently however it began beeping for no reason, and I couldn’t get it to stop other than by removing the batteries. So I bought a new one and decided to tear down the old one.
Back in 2016, TI introduced a line of what they called “nanopower op amps”. Where older op amps like the 741 use around 2 mA, and more modern ones might reduce that to perhaps 100 uA or so, TI’s ultra-low power devices consume just a few hundred nA. This enables the design of things like smoke alarms and temperature monitors that can work for a decade on a single battery charge.
This is the LPV801, a single channel op amp that uses just 450 nA. It’s not very fast: with just 8 kHz of unity-gain bandwidth it’s useless for audio, but ideal for slow-moving things like temperature sensors. A dual version (LPV802) is also available, as are single and dual versions with reduced offset voltage (the ‘811 and ‘812 respectively).
Inside we find this neat little design. Five bond pads are bonded to the five pins on the package; two additional ones on the top row are used for testing. In the top-right corner is an L-shaped alignment marker, which is used during laser trimming.
Continue readingRegular readers of this blog will have noticed that the 741 op amp features quite often. Apparently I’m not the only one with an interest in this venerable amplifier; the Wikipedia page on op amps contains a detailed description of the 741, several books and web sites describe and even celebrate the chip’s history, and you can buy a kit to make a large-size discrete replica from a company called Evil Mad Science Labs. I bought one of these because I thought it looked rather cool.
On the picture above you can see the 741SE compared to an original LM741. I got the SMD version of the kit, although you can also buy one that uses through-hole components and is shaped like a giant DIP package. Still, even the SMD version is enormous compared to the real chip, which got me thinking: would it be possible to make a discrete equivalent of the 741 in a space equivalent to an actual DIP chip?
Continue readingThe good old 741 op amp is way more versatile than I first thought. After dissecting two sets of varying designs (here and here) I managed to get my hands on even more different varieties, from all over the world, from the 1970s to the 21st century.
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.
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