One of the most enjoyable parts of electronics design is getting excellent performance with rock-bottom parts cost. The right circuit can produce exceptionally good speed, noise, and accuracy specs from very low-cost parts. A case in point was a project from December 2016: a time-domain reflectometer (TDR) for a liquid level sensing application in industry.
James Elbert (Jim) Thompson was a well-known chip designer who used to be a regular on sci.electronics.design. He last posted in July 2018. As he was very sick at the time, we presume that he has died, but no obituary has so far turned up. He was born on February 29th, 1940, and used to say that he was looking forward to his 21st birthday in 2024.
InGaAs heterojunction FETs are magic parts—fast, strong, and extremely quiet. They're also called pseudomorphic high electron-mobility transistors (pHEMTs), because they use a 2D quantum well to to force the conduction electrons to move in a plane without much scattering. My fave Avago ATF38143 pHEMT was discontinued, but luckily Mini-Circuits stepped into the breach with their very nice SAV-551+ and its siblings, which are similar enough that the ATF SPICE model can be hacked up to work with them. (RF companies like Mini-Circuits never seem to supply SPICE models for some reason.) In one post on the 'purpose of precision' thread on sci.electronics.design, I noted that the Avago ATF38143 model I had posted awhile back predicted way, way too much low frequency noise. The real pHEMTs tend to have a pretty accurately 1/f PSD with corner frequencies between 10 and 50 MHz and flatband noise of around 0.3 nV/√Hz, about 10 dB quieter than the best JFETs, as well as being 20 times faster.
At EOI, we've been building advanced instruments for a long time. One reason for our success is our large inventory of working designs, and another is the way we go about doing it. This post walks through a typical sort of development plan for a challenging customer requirement, in the form of a hypothetical email proposal outline for a fibre-coupled noninvasive glucose sensor similar to the one we did in 2013.
(You can also read about a recent project that went a lot like this, except with a single prototype stage.)
In How We Work, we gave an overview of how we build instruments, from the initial feasibility calculation (or photon budget) to delivery of the first production units.