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Low Frequency Noise In InGaAs Heterojunction FETs

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.

How We Work

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.)

Silicon Photomultiplier (SiPM, MPPC) System for Cathodoluminescence

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.

Noninvasive Transcutaneous Blood Glucose: A War Story

Here at EOI we have three main kinds of project. One is our internal technology development projects. Some of these fail, mostly because they tend to be insanely hard, but the ones that pay off give us important new capabilities.

High-Value Ceramic Capacitors: They Stink, and You Can't Get Them Anyway

There are widespread shortages of electronics parts at the moment, especially passives.  Quoted factory lead times are 40 weeks or thereabouts, and since the industry is capacity-limited, it isn't clear that the situation is going to get better any time soon, so everybody's starting to panic.   Given all this churn I've been spending an unconscionable amount of time lately finding suitable replacements for out-of-stock parts.