Differential calculus is the study of rates at which quantities change. To find the derivative of a waveform at a specific point, we draw a tangent line through the point. The slope of the line, Δy/Δx, equals the derivative of the function at that point. Integral calculus quantifies the area bounded by a curve and […]

# Featured

## Understanding the lock-in amplifier, Part 2: The homodyne solution

The lock-in amplifier allows tiny signals from sensors to be captured with precision despite unavoidable noise limitations and other test and measurement challenges of the signal chain. Part 1 of this article looked at the changes of capturing low-level signals such as from a photodetector despite unavoidable signal-path noise, drift, offsets, and other imperfections. This […]

## Understanding the lock-in amplifier, Part 1: The sensing challenge

The lock-in amplifier allows tiny signals from sensors to be captured with precision despite unavoidable noise limitations and other signal-chain test and measurement challenges. There are some basic test and measurement instruments common to scientific labs and engineering benches of all types, whether electronic, biomedical, chemical, optical, or mechanical. Among these are the digital voltmeter, […]

## Applications and algorithms for quantum computing

Developing the hardware for quantum computing and hybrid quantum/classical computing systems is only one step in developing practical quantum computing solutions. Development of quantum algorithms and related software programming of the qubits is required to implement practical applications using quantum approaches to computing. Earlier FAQs in this series looked at the basics of quantum computing, […]

## Online calculators that are handy for EEs

Online calculators have proliferated. Consider that one site dubbed omnicalculator.com now hosts over 1,800 online calculators in various disciplines. But when it comes to electronics and engineering, the pickings are slimmer. Calculatoredge.com provides numerous online calculators for engineers of which a little over 100 are in electronics and electrical engineering. That brings us to Digi-Key […]

## Merging quantum and classical computing in a hybrid system

Practical quantum computing requires connections to the outside world. Those connections may be for collaboration between a quantum computer and an external computing resource such as a supercomputer. They can simply output the results of the quantum computations in a manner accessible and usable by human operators. In either case, there’s a paradox between the […]

## What are the basics of quantum computing?

The concept of quantum computing has been around since the early 1980s when physicist Paul Benioff proposed a quantum mechanical model of the Turing machine. Benioff’s ideas were built upon by Richard Feynman, Yuri Manin, and others, who suggested that a quantum computer had the potential to simulate things that can’t be done using classical […]

## What is the difference between variable reluctance and eddy current speed sensors?

Both variable reluctance (VR) and eddy current (EC) technologies provide contactless speed sensors based on interaction with a magnetic field. A variable reluctance sensor can be thought of as an ac generator with an output voltage proportional to speed. With its self-generating electrical signal, a VR sensor does not require an external power supply. The […]

## Quantum computing system architectures

There are a variety of possible physical embodiments of quantum computers. This FAQ will explore several of those possibilities. Qubits, Hamiltonians, and decoherence are three important concepts needed when discussing various approaches to quantum computing. Check out the first FAQ in this series for a more detailed discussion of “What are the basics of quantum […]

## Next L-Prize announced: This time, it’s commercial LED lighting

The DoE-sponsored competition that gave rise to the first economical 60-W LED bulbs is operating again. The new goal: More innovative commercial lighting. The Bright Tomorrow Lighting Prize (L-Prize) began in 2008 with the goal of accelerating development of LED-based replacement lamps that met extraordinarily-stringent performance and life goals. Back then, there were such things […]