Most electronic systems that need an accurate clock, which is to say most microprocessor-based systems, use a quartz oscillator. You’ll typically see a metal package somewhere near your chip that contains a slice of quartz which resonates at a certain frequency thanks to the piezoelectric effect.
Quartz crystals are cheap and provide a very accurate clock frequency, but they take up quite a bit of space and are sensitive to shocks. To deal with those two problems, fully on-chip oscillator systems have been available since about 2010. These use micro-electro-mechanical systems (MEMS) technology, which involves the manufacture of tiny moving structures on a chip. Their price is typically higher than that of a quartz crystal however, and their frequency stability and phase noise performance are often a bit worse. Today we’ll have a look at a few different MEMS oscillator chips and see what they look like inside.
First up is the Si501 by Silicon Labs. It’s an 8 MHz oscillator built using what Silicon Labs call CMEMS technology, which means that they integrate the MEMS bit on the same chip as the rest of their circuits. The package looks rather anonymous, with just a cryptic part number and no manufacturer’s logo. Silicon Labs have since sold their MEMS oscillator business to Skyworks, so future versions of this chip might have a different marking.
I recently read a forum thread where someone showed how a set of LME49710s that he bought online didn’t function the way they should. Although the chips apparently contained an op amp, they were unable to amplify a 60 kHz square wave and output a triangle wave instead. This means that the op amps’ slew rate is too low: the LME49710 is specified to reach 20 V/us, but these chips only managed 0.5 V/us or so.
The thread’s author asked if anyone could help identify his chips, and I offered to examine them for him. A few days later I received the op amps in the post. They were clearly marked with the National Semiconductor logo and “49710” as a model number:
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.
Digital isolators are a modern replacement for optocouplers: components that can bring a signal from one place to another without connecting those two places electrically. They’re essential parts in equipment that connects to a dangerous voltage on one end (mains power usually) and comes into close contact with something sensitive on the other (humans, usually). Since they’re safety-critical components, manufacturers show off all kinds of safety certificates and qualifications to convince their customers that their isolators won’t electrocute anyone by mistake.
Today we’ll look at one of the cheapest digital isolators out there: the π120u30, made by 2Pai semiconductor, which costs less than 20 cents in large quantities.
Texas Instruments has a nice selection of motor driver ICs. Where in the old days you’d often have to make your own H-bridge out of discrete transistors, figure out how to drive their gates, and then generate the right signals to spin up, reverse, brake or coast your motor, nowadays you can get all these functions integrated into a single chip. Today we’ll look at the DRV8876, which is a rather small chip that can nevertheless dump up to 3.5 A into a motor’s windings.
Today we’ll look at a couple more versions of the 555 timer. Like the 741, this chip has been produced by many different manufacturers in the nearly five decades since its introduction by Signetics in 1972.
First up is RCA’s CA555. Packaged in an 8-pin DIP (which is what the “E” in “CA555CE” stands for), this is a “C” spec which can work at up to 16 V, unlike the CA555E that is spec’ed up to 18 V. I’m not sure what the actual difference between these two would be; I guess the chips were sorted after production, with parts that marginally failed some spec at 18 V being demoted to “C” versions.
The LIS3DH is an accelerometer, designed and manufactured by STMicroelectronics. Like most accelerometers today it is a MEMS device (Micro-Electro-Mechanical Systems), which means the sensing function is made from silicon and integrated into an IC process. Special etching techniques are used to create tiny moving parts that can bend in certain directions, along with sensors that can detect that movement.
MEMS accelerometers are used in many electronic devices: your phone that detects whether you’re holding it horizontally or vertically, your games console that can sense which way you’re moving the controller, or your car that can detect the speed and direction in which you’ve just crashed so it can properly deploy the airbag.
The LIS3DH is housed in a little LGA package that measures just 3 x 3 mm2. Oddly there’s no ST logo or marking on the package. The “ON5nn” production code could actually trick you into thinking this is an ONSemi part.
After a bit of browsing on eBay I found several “new” versions of my favourite classic op amp, the 741. We’ve already seen about twelve different layouts so far, but today we’ll see that there are still more out there.
Starting with the oldest, we go back more than four decades to 1974. Texas Instruments at that point sold the SN72741, adapting the original Fairchild part number to their own nomenclature: SN stands for “Semiconductor Network”, meaning “integrated circuit”, while the numbers indicate the product series and temperature range (0 to 70 °C in this case; there was also an SN52741 with a wider temperature range).
If there’s a classic analog chip even more iconic than the 741 op amp, it has to be the 555 timer. Released just three years after the 741, it similarly took the world by storm, selling billions of units over five decades. Quite unlike the 741, which established op amps as a common IC type, the 555 has remained largely in a class of its own. 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.
Designed by Hans Camenzind in 1972, its story is described in detail in Camenzind’s own book Designing Analog Chips. I highly recommend reading it (available on paper or as a free download) if you’re interested in analog IC design. In Chapter 11, Camenzind shows the schematic of the original 555 timer: