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Once upon a time, the place known as “Silicon Valley” was once filled with factories that designed and built silicon-based products. Hard to believe these days but really truly it was once was. I lived there during the fading days of such … and lived just up the street from a company known as Signetics.…

The flow of water in a hose is often used as an analogy for electrical current. Let’s see about that, first considering the electrical parameters. Define a few values: Avogadro Number nA = 6.02214e23 particles/molMolar mass of copper mM = 63.546 g/molCopper density cu = 8.960 g/cm3 Electric charge q = 1.60218e-19 CElectron mass Me…

I’ve not kept up with this technology in 15 years or more – after my time in mineral and oil/gas “prospecting” instrumentation, life took me back to spacecraft. Much if not most of my career has been involved with space-based instrumentation with the primary challenges being temperature, radiation, mass, volume, and survivability – but by…

One topic I had been interested in for some time is the problem of measuring atmospheric constituent gases from aircraft using molecular absorption methods. I was lucky enough to be employed at NASA where some of this research was based Various gaseous constituent molecules tend to absorb photons of very specific wavelengths – so the…

Sometime long ago I was asked to analyze a temperature sensing system which had an operating temperature of “about” 100K with a control limit of ±1mK. Stability of temperature is more important than the absolute value which is why I say “about 100K”. The sensor excitation is rated at 10 mVmax; the sensor response time…

At times, empirical data becomes both useful and necessary. I wanted to establish a practical lower measurement limit for a group of photodiodes. The following represents measurements made with an Agilent 3458A of a Hamamatsu G6854-01 InGaAs photodiode. The diode was optically sealed with zero-bias. Measurements were collected for just over 8 hours – 8PM…

My notes suggest this was an interview question at one time. What I didn’t note is when, who, and whether I gave it or received it. The date stamp suggests late 1990s/early 2000s. State assumptions and determine the voltage at the output. Assumption: Neither transistor is saturated. Base current is zero. Voltage at NPN base…

More ideas that didn’t go anywhere than those that did. Here are three that didn’t go anywhere. Brief Discussion of Selected Current Research Interests: 1) Hazardous Waste Site Monitoring by Non-Invasive Methods (to be submitted to NSF June 2005) A proposal to detect and possibly identify leaking subsurface fluids by non-invasive magnetic field detection is…

A circuit that I always felt useful yet never had the opportunity to actually put into a circuit. Drs. John Kleppe and Larry Huelsman introduced me to these networks. Dr Huelsman was one of the early developers of these networks (and one of my MSEE advisors). Initial applications were for developing synthetic inductances. First introduced…

These are defined as “exact” fundamental constants by NIST k = Boltzmann Constant = q = Electron Charge = Thermal Noise A current is defined as the movement of charge over time:     Usually, current is considered as a macro effect, but here I get down into the fuzzy details. Electrons wiggle at temperatures…

Noise in RC Networks is kT/C, not 4kTRf The thermal noise in a RC network is determined by the temperature and capacitance; resistance and frequency are not first-order factors. Noise Equivalent Bandwidth (NEB) Consider a 1st-order RC system … such as a passive detector with time constant as a basic parameter. Such a system may…

A few stray discussions of pn- junctions and how they interact with temperature.

Rise time is defined as the time for a waveform to transition from 10% of the final steady-state amplitude to 90% of that amplitude (fall time is defined the same way … only on the falling edge). Calculating for a 1st-order response:             Define the low-pass bandwidth by the frequency…

Copper is copper, right? A great conductor. Not the best (that would be silver), but 2nd-best works … especially when considering cost and mechanical properties. (Why, oh why … do people pay for gold audio wires?) From the “CRC Handbook of Chemistry & Physics“:     *Note: nickel is paramagnetic with relative permeability: Although some…

The Wheatstone Bridge is a simple circuit capable of making very accurate measurements. The basic network was actually proposed in the 1830s by Samuel Christie but named after Charles Wheatstone who publicly presented it – as Christie’s work – in 1843. It remains the basis for many transducer interface networks to this day.    …

I once worked on a program that collected hundreds of Gbytes of data during 4 and 8 hour flight-based measurements. There was so much data collected that generating backups at the end of an experiment was interfering with flight turn-around time. Consider: a parallel 16-bit converter clocked at 2 MHz and running four hours straight…

Line termination: seems it should be a basic bit of knowledge for a practicing designer. However, it is not so simple as sticking a resistor on the line and calling it good – unless coax, the termination resistance likely won’t be 50 or 75 . A twisted-pair line for example hs an impedance of about…

When I design a field instrument, I need to consider the power supply as well … actually the power supply needs to be considered an integral part of the system, not simply a matter of “VDD goes here, GND goes there”. So this led to a few years spending my time developing switching regulators for…