When to use an op-amp?

russ_hensel

Joined Jan 11, 2009
825
All the time. A bit of overstatement. In some applications the op amp may be overkill. Limitations of op amp.

* hard to get frequency response over 100 k hz ( but there are some video op amps that go much faster.

* output current in range of 10's of ma. Use transistor for boost.

Advantages:

* differential input
* high input imped. ( for most common types )
* low parts count
* simple equations for predicting output
* useful in wide variety of circuits.
* response from 0 hz.
 

Adjuster

Joined Dec 26, 2010
2,148
High frequency tuned amplifiers also more often use transistors, although the vast bulk of circuits are integrated nowadays. Op-amps as such are not common above perhaps some MHz (this limit has been moving up over time - I may be out of date). Some higher frequency amplifiers have specialised designs, not necessarily with differential inputs.

At really high frequencies, from hundreds of MHz into GHz, amplifier structures tend to become simpler. It is difficult to have a feedback loop extending over many stages at these frequencies without encountering problems with phase lag.
 

Wendy

Joined Mar 24, 2008
22,146
Op amps tend to have idealized characteristics. Folks have already mentioned where it isn't used, but in many cases it is fun to play with where it can be used, understanding that sometimes it just doesn't work.

Overall it is a bit like digital, when it works as expected it can be very satisfying.
 

Thread Starter

jaygatsby

Joined Nov 23, 2011
182
All the time. A bit of overstatement. In some applications the op amp may be overkill. Limitations of op amp.

* hard to get frequency response over 100 k hz ( but there are some video op amps that go much faster.

* output current in range of 10's of ma. Use transistor for boost.

Advantages:

* differential input
* high input imped. ( for most common types )
* low parts count
* simple equations for predicting output
* useful in wide variety of circuits.
* response from 0 hz.
Thanks! Why is differential input considered such an advantage?
 

Audioguru

Joined Dec 20, 2007
11,249
A differential input can show the voltage difference between two signals. One can be the input and the other can be negative feedback that reduces the extremely high gain to a useable amount and then it reduced the distortion to almost nothing.

A transistor produces very high distortion.
 

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