Here's my summary
What is an OpAmp? :
It's a high gain, high input resistance, differential amplifier.
Why is that Useful? :
When a very high gain amplifier is used in conjunction with feedback components then the overall characteristics of the resultant circuit are determined almost entirely by the feedback elements, and not by the actual amplifier itself. This made the Op-Amp an ideal building block as, in principle, a single design opamp could be used for a multitude of different purposes simply by changing the feedback components (which are usually just simple passives like R's and C's).
In a nutshell, the advent of the integrated circuit opamp made it possible to have a single mass produced analog IC that could be easily configured to produce a wide range of different functions by just adding R's and C's (and sometimes other components) as required. The type of analog circuits that can be easily built from opamps include :
- Amplifiers of precise gain (inverting, non inverting or differential)
- Filters (eg high pass, low pass, band pass)
- Sample/Hold circuits
- Precision Rectifiers (absolute value function)
-Voltage Limiters (clamps)
- Differentiators (time derivative)
- Integrators (time integral)
- Adders, subtracters (and other mathematical functions).
- Numerous other things.
Is the OpAmp now Obsolete ? :
Not really, though the scope of their application is decreasing. To really answer this we should try to divide the applications into two main areas
1 - Basic Amplification and
2 - Analog Signal Processing.
While the above division is not really a clean one (many applications blur the line between the two categories and in a sense amplification could be considered as a simple form of signal processing anyway) I chose that "division" mainly to point out that it is more in the second area that the OpAmp is tending to become obsolete.
Of course the more difficult or intricate the analog signal processing application then the sooner it was (or will be) replaced by digital technology. For example the most extreme case I could think of would be that of the analog computer, where racks and racks or op-amp integrators, amplifiers and adder/subtracters, were patched together to simulate the differential equations some physical system under study and hence to predict it's behavior. Obviously these went he way of the Dinosaurs many decades ago. (BTW, my old University actually had one of these bad boys tucked away in a basement. Not in use hehe, but I did get to play around with it a bit before it eventually got sold off for scrap).
In general analog signal processing is being increasingly replaced by digital signal processing, but just the same there are still many simple applications where analog signal processing can be done more easily and more cheaply than a DSP. So don't be fooled into thinking they are no longer used. In particular, even where a DSP is used, it will generally require some analog "pre-processing" in the form of a pre-amp for good SNR and a pre-sample low pass filter to avoid aliasing (Nyquist limit). I'd say that OpAmps will still be around for the foreseeable future.
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