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Op amp beginner's questions

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nForce:
1) Which configurations of op amps are more preferable? (Non-inverting or inverting)? In which cases?

2) How did this guy get Vout with the reactance of a capacitor (yellow)? (Picture of the integrator in the attachment)

Thanks.

rstofer:

--- Quote from: nForce on November 25, 2018, 05:08:38 pm ---1) Which configurations of op amps are more preferable? (Non-inverting or inverting)? In which cases?

--- End quote ---
The big difference is whether the amplifier inverts.
http://pediaa.com/difference-between-inverting-and-noninverting-amplifier/

--- Quote ---2) How did this guy get Vout with the reactance of a capacitor (yellow)? (Picture of the integrator in the attachment)

--- End quote ---

Suppose the Xc value was just a resistor and called Rf.  Then the standard gain equation would -Rf/R.  The only change is that the feedback is a capacitive reactance rather than a simple resistance.  This assumes we are interested in the circuit as an integrator but it can also be a low pass filter.

In the case of the integrator, the equation we care about is the one with the integration.  This is the fundamental building block of analog computers and this is a topic that just fascinates me.  I know, simple things...

The thing is, a second order differential equation like my''+dy'+sy = 0 shows up in so many areas of physics and electronics.  It is just fun to model it on an analog computer and watch it run.  Better yet, instead of = 0, substitute = A*cos(wt) and watch what happens when wt is less than the resonant frequency, equal to the resonant frequency (watch out!)  or greater than the resonant frequency.  FWIW:  m=mass, d=damping coefficient, s=spring constant  Look at equation 1 here and note the similarity:
http://www.math.ubc.ca/~feldman/m121/RLC.pdf

ETA: that little graph after equation 4 shows what happens to any second order differential equation when it is excited at its resonant frequency.

What a marvelous little circuit!

Audioguru:
If I do not need inverting then I always use a non-inverting opamp since its input impedance is very high or extremely high then the value and cost of an input coupling capacitor can be small. An inverting opamp circuit has a fairly low input impedance.

The integrator is a linear lowpass filter that cuts high frequencies.

Wimberleytech:
A non-inverting configuration has more bandwidth for the same flat-band gain.

Zero999:
The circuit attached to the original post needs to have some DC negative feedback, otherwise the op-amp's output will probably saturate at one rail or another, due to the bias currents. There should be a high value resistor, in parallel with the capacitor to stabilise the circuit. If you're using a J-FET/CMOS input op-amp, you might be able to get away with it, as the leakage current through the capacitor could be sufficient, but it's still bad practise.

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