Saturday, 9 December 2017

Op-amps Make Life Better

Op-amps thrill me.  I mostly employ them as instrumentation amps, plus AF small signal boosters or filters.  With simple math (often embedded in software or spreadsheets) , we can calculate design parameters such as gain, frequency response or better yet, a stage's transfer function.  Once built, you can measure and analyze your circuit's outcomes in your lab.

I get many ideas and information from peer-reviewed journals. If your affiliated with a university, then your librarian may have access to many free journal articles.  Occasionally, you must purchase a journal article if you deem it essential to your progress. This supports the author(s),  publisher and in turn, spawns more research and journal articles. Circle of life stuff in academia.

Article abstracts provide a good way to learn too.  I think of them as free little packets of information.  At the very least, they may inspire you down a new, exciting path. I read a lot of abstacts on various subjects.

Further, I try to devote some study time to instrumentation circuitry because you get exposed to some brilliant engineering techniques, historical perspectives and often enough, cool new parts.  Apart from the usual RF measurement gear, I hold a special interest in chemical and atmospheric measurement circuits.

OK, back to op-amps:

A case in point follows. Op-amps prove essential for modern instruments -- without them, our digital circuits often wouldn't have any usable voltage to work with.  Analog isn't dead Malcolm!

This abstract sums it up perfectly.

Abstract

The Analog Revolution and Its On-Going Role in Modern Analytical Measurements.

The electronic revolution in analytical instrumentation began when we first exceeded the two-digit resolution of panel meters and chart recorders and then took the first steps into automated control.

It started with the first uses of operational amplifiers (op amps) in the analog domain 20 years before the digital computer entered the analytical lab. Their application greatly increased both accuracy and precision in chemical measurement and they provided an elegant means for the electronic control of experimental quantities.

Later, laboratory and personal computers provided an unlimited readout resolution and enabled programmable control of instrument parameters as well as storage and computation of acquired data. However, digital computers did not replace the op amp's critical role of converting the analog sensor's output to a robust and accurate voltage.

Rather it added a new role: converting that voltage into a number. These analog operations are generally the limiting portions of our computerized instrumentation systems. Operational amplifier performance in gain, input current and resistance, offset voltage, and rise time have improved by a remarkable 3-4 orders of magnitude since their first implementations.

Each 10-fold improvement has opened the doors for the development of new techniques in all areas of chemical analysis. Along with some interesting history, the multiple roles op amps play in modern instrumentation are described along with a number of examples of new areas of analysis that have been enabled by their improvements.

Reference

Enke, C. G. (2015). The Analog Revolution and Its On-Going Role in Modern Analytical Measurements. Analytical Chemistry, 87(24), 11935-11947.


With new appreciation for op-amps from reading this article, I plan to get on the bench and have some fun applying them.  Who knows, I might blog some of these circuits 1 day.

Also, please continue to cherish and support science.  Evidence -- not hype nor hope should guide our daily decisions.

2 comments:

  1. What about OPA1602, OPA1612 and OPA1662 OPA2134, OPA1642, OPA1652 etc???

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  2. All great parts Regis. Everything in context -- I tend to choose a part to suit the situation and think we can get carried away putting an expensive part into a slot when a cheaper part will work just as well.

    If you have a low DC rail-rail voltage and want maximal output dynamic range -- then, for sure; put in a rail-to-rail op-amp.

    I tend to use the NE5532 for most audio stuff and occasionally go with a LM4562. The 4562 can oscillate though!!!

    In an instrumentation amp or say a fancy background remover circuit, I might ply a low bias current op-amp like the LT1677 to reduce offset in my circuit. In some cases for the latter circuit, the offset is temperature sensitive and causes a meandering circuit response so an expensive op-amp like the LT1677 is perhaps justified.

    Measuring the difference is key. I'm currently making SS guitar amps and the tone myth stories prove endless.

    I love this video by Ethan Winer:
    https://youtu.be/BYTlN6wjcvQ

    Pretty much debunking all the legendary stories and promoting
    what to measure and how to measure. Also our brains play tricks on us in nearly every moment.

    Cheers!
    V

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