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Thread: Let's amp up the discussion on OpAmps (Operational Amplifiers) and how they work

  1. #1
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    Default Let's amp up the discussion on OpAmps (Operational Amplifiers) and how they work

    There has been some reference on PLF about opamps used for laser signal conditioning and an uncertainty about how they work. Why don't we create a discussion thread to make more transparent their basic use and functionality for analog signal processing.

    Many on PLF have a good working knowledge of these miraculous little integrated circuits that come in many forms such as single, dual and quad amplifiers in a single IC package. In the mid 1960's an engineer at Fairchild Semiconductor made the first operational amplifier on a single integrated circuit chip, the uA709.

    From https://www.computerhistory.org/revo...omputers/3/156

    "An op-amp, technically, is a high-gain voltage amplifier with differential inputs. Using appropriate negative feedback, a single op-amp can add or subtract two voltage signals, multiply by a constant, or integrate voltage over time. Stringing together many op-amps lets one compute complicated formulas."

    I was first introduced to this opamp in 1970, how it worked, what it could do as an analog amplifier/signal conditioner/signal processor because I was interested in making smaller, compact audio recording and mixing equipment. Soon there was the 739, a low-noise, linear audio spectrum response version, good for use as a low-impedance microphone amplifier. Other improved general purpose opamp versions followed like the 741, 748, 747 (a dual 741), the LM348 (a quad 741). Today, the TL07x and TL08x are the most common versions of this analog operational amplifier we see today.

    But, for the most part op-amps are intended to increase, decrease, mix, alter frequency responses of one or more DC and/or AC electronic signals. The term "amplification" can be an increase or decrease of given frequency range of the input signal. In general they are designed to operate within a frequency spectrum from DC to hundreds of kilohertz or up to 10 megahertz in some cases. Making them operate in a linear, predictable manner within the DC and audio spectrum is probably the easiest. Extending their frequency range in the 100's of kilohertz and higher takes more care and attention.

    The most basic op-amp circuit forms are:
    1. The voltage follower or signal buffer amp
    2. The inverting amplifier
    3. The inverting/mixing amplifier
    4. The non-inverting amplifier

    Signal inversion means if the input voltage value at any given instant is positive then it's corresponding output is negative, therefore for a given input signal phase it's corresponding output is 180 degrees out of phase with the input.

    I found this link that help define the single most important features of the operational amplifier, "The Golden Rules of Op-Amps.

    https://www.circuitbread.com/ee-faq/...les-of-op-amps

    The 1st most important take-aways from "The Golden Rules of Op-Amps" is the greater an op-amp's Open-Loop Gain, the greater the amount of Negative-Feedback is available that can be used to create very linear signal processing over a wide frequency range. All op-amp spec sheets show a graph typically labeled "Large-Signal Frequency Response" or in the case of the TL07x or 8x "Large-Signal Differential Amplification & Phase Shift vs Frequency". This graph is used to determine what an op-amps frequency response will be from DC to a higher frequency for a given amount of gain (Rf/Rin). It is sometimes referred to as a Bode Plot. (bo-dee)

    Click image for larger version. 

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    The 2nd most important take-away is that the more signal gain an op-amp has the less linear frequency response range the amplifier has. For audio and laser signals this may not be a factor as long as the signal gains (aka amplifications) are kept small (1-20) with the best frequency response occurring when the gain is just multiplication factor of 1.

    The 3rd most important take-away is that most op-amps (not all) can be powered by a single voltage (+ or -) or dual bi-polar voltage (+ and -) power supply. If the op-amp needs to respond down to DC signal levels and a single is used the output signal will be centered around half the value of the supply voltage. When dual bi-polar supplies are used then the output voltage will be centered around 0v (unless an intentional DC offset voltage is also added or subtracted to the input signal).

    The 4th most important thing to know, not mentioned in "The Golden Rules of Op-Amps", is that as long as resistors are the only input and feedback components used the amplifier's response will include the highest possible frequencies based on the amplifiers signal gain down to DC. Whenever capacitors or inductors (capacitors being more common) are used in series or parallel with the input and/or feedback resistors they change/alter the amplifiers linear frequency response in some manner.
    Here's an example. Let's say the TL084 op-amp is to increase the input signal by a gain of 5. It's "Large-Signal Differential Amplification & Phase Shift vs Frequency" graph shows that with a gain of 5 its frequency response will start falling off around 800KHz. But all your design requires is a faithful linear output signal response from DC to 20,000Hz. You could add capacitor(s) to modify the amplifier to become a low-pass filter whose response is linear from DC up to 20,000Hz.

    Draw a horizontal line from the vertical axis on the left mid-way up between 0 and 10 to the 1 power, extend the line over until it intersects with the line that slopes down and to the right. At this intersection, look directly below on the horizontal axis labeled Frequency and read off the value. At this frequency value the amplifier begins attenuating the resulting output signal at the rate of 70.7 percent for each octave higher in value.

    Discussion is welcome.
    Last edited by lasermaster1977; 02-09-2023 at 19:28.
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    You're right, but I think you might have more success getting people who grew up with computers to take up the kazoo than analog electronics.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

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    Quote Originally Posted by laserist View Post
    You're right, but I think you might have more success getting people who grew up with computers to take up the kazoo than analog electronics.
    You are probably right, but most DACs of yore and today need some form of op-amp analog output circuitry, although some have them built-in and many of these are capacitively coupled, intended for audio bandwidths and exclude DC unless analog level shifting is implemented. That's mostly where I'm coming from with this "offering".

    I teach kazoo as well! Laureen Bacall taught me, "You just put your lips together and blow".
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    Oh sure they'll buy a DAC that has op amps in it, but building something that fills the gap - that lets them create and interact in real time - nope - it's a paradigm thing...
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

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    Quote Originally Posted by laserist View Post
    Oh sure they'll buy a DAC that has op amps in it, but building something that fills the gap - that lets them create and interact in real time - nope - it's a paradigm thing...
    Sorry, I meant parallel DAC chips or SPI, I2S or I2C chips with built-in DACs and/or ADCs that execute software let me create and interact in real time, or not.
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    It's funny how things go around and come around. There was a guy long ago - he played guitar. With lasers he could never get that it didn't matter if you started to turn the knob on the beat - it was when the effect of turning the knob was visible to the audience... Today most "shows" have this flaw - for me - where they are just running with the tempo of the music instead of a much deeper synergy because it's really difficult to do something on a timeline that's incredibly easy to do with a knob or a joystick.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

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    Quote Originally Posted by laserist View Post
    It's funny how things go around and come around. There was a guy long ago - he played guitar. With lasers he could never get that it didn't matter if you started to turn the knob on the beat - it was when the effect of turning the knob was visible to the audience... Today most "shows" have this flaw - for me - where they are just running with the tempo of the music instead of a much deeper synergy because it's really difficult to do something on a timeline that's incredibly easy to do with a knob or a joystick.
    I heartily agree. Just so there is no uncertainty, I much prefer real-time interaction to programming to a timeline. But then there can be many variations, used musically and/or visually, that marry the functionality, to some degree or another, of both methods.
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    Gone are the days of being able to walk in to RadioShack, Olson's, Phil-Cap, etc... and buy op-amps and other electronic bits to make homebrew gear. I used to know all the people who worked in those places and had many great conversations.
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    Quote Originally Posted by james View Post
    Gone are the days of being able to walk in to RadioShack, Olson's, Phil-Cap, etc... and buy op-amps and other electronic bits to make homebrew gear. I used to know all the people who worked in those places and had many great conversations.

    opamps are just Electronixís that are always being bothered by use organic types and just want to be left alone to find their center and stay grounded. Some move faster than others and some love to be coupled I put some like it raw. Some only like to be on one side of the potential of existance while others like it both ways. Some just canít help but invert every input while others donít. Some like feedback to help control their urges while others just like to slam the door. But most of all they just want to be left alone to settle on the status qou and stay grounded.

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    Quote Originally Posted by kecked View Post
    opamps are just Electronixís that are always being bothered by use organic types and just want to be left alone to find their center and stay grounded. Some move faster than others and some love to be coupled I put some like it raw. Some only like to be on one side of the potential of existance while others like it both ways. Some just canít help but invert every input while others donít. Some like feedback to help control their urges while others just like to slam the door. But most of all they just want to be left alone to settle on the status qou and stay grounded.
    Love this!!

    I started building all kinds of electronic kits and radios since I was 9 years old, starting with 50-in-1 kits and most of the Radio Shack P-Box kits. I built my own stereo amp and pre-amp from Dynaco kits in high-school. And I've spent lots of time building all sorts of little electronic projects over the years since then.

    Then a several years ago I got into Arduino development which renewed my interest in the hobby building all kinds of fun stuff (and now ESP32 development).

    But two years ago I had heard of "op-amps" but didn't know what they were or what they did. I never needed one. That is, until I started on my ILDAC-32 and ILDAC-WAV projects. It wasn't a matter of just following a schematic and wiring things up (which is all I did at first) -- the more I got into it, the more I had to understand what op-amps actually do and how they work in order to improve the project. Thanks to watching tons of videos on op-amps, and ABerry basically giving me a crash-course in op-amp theory via firehose (thanks!), I now understand how these little chips of magic work. Their simplicity is amazing. I'm really surprised I never really came across them in all my previous projects. For instance, understanding the DAC chips in ILDAC is simple -- you feed it a digital stream of numbers, and you get a voltage out the back. Easy. But op-amps? Not so straight forward. But once it clicked, it was an "a-ha" moment.

    I do wonder how the genius who first invented the op-amp put it together, and if he knew how fundamental they would become in electronics in the future.

    Here's some of the best op-amp intro videos I really benefited from:
    https://www.youtube.com/watch?v=7FYHt5XviKc
    https://www.youtube.com/watch?v=kF1wGW-h4Y8
    https://www.youtube.com/watch?v=aR9ILhbG4AE

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