Operational Amplifier (op-amp) Introduction – Part 1 of 5

All this theory and knowledge about op amp is what I learned from a book called ‘Practical Electronics for Inventors’ by Paul Scherz and Simon Monk. This is a fantastic book for electronic hobbyist like myself, quite in depth and clear in explanation.

I am not associated with the authors and I do not get any commission if you buy this book. This is really a good book for electronics enthusiast. This blog is my learning journey.

Parts of op amp and its pin configuration on the actual component.

Parts of a op amp are:

  • +ve power supply(+Vs) and -ve power supply(-Vs).
  • non inverting input (V+) and inverting input (V-).
  • Output Vout.
  • Some specialized leads.


Basic operation of op amp:

  • When V+ (non inverting input) greater than V- ( inverting input) , the out Vout will saturates towards +Vs (+ve supply).
  • When V- (inverting input) greater than V+ (non inverting input), the Vout will saturates towards -Vs (-ve supply).

Refer to below diagram for visual explaination:

Top is non inverting setup and bottom is inverting setup. Inverting setup cause a 180 degree shift between the input and output.


Different op amp setup(configurations):

  • Inverting amplifier: Vin is connected to V- , and this caused the output (Vout) to be inverted compared to its input (180° shift).
  • Non inverting amplifier: Vin is connected to V+ , and this caused the output (Vout) to be in phase with its input ( +ve input +ve output, -ve input -ve output ).
  • Take note that Vout reaches Vs (supply) saturation in both -ve and +ve direction.

Negative feedback configuration:

  • make op amp more useful
  • the gain of the output can be controlled, and prevent Vout from saturation
  • components are places between the Vout and V- (usually resistors and capacitors) and this make the op amp to be more than just amplification.
  • with a -ve feedback circuit, op amp can be voltage regulator, current to voltage convertor, voltage to current convertor, oscillator, math circuit, waveform generator, active filter, active rectifier etc…
  • -ve feedback is more common than +ve feedback
Inverting amplifier. RF value will affect the gain for Vout.

Inverting amplifier formula: Vout = – (RF/Rin)*Vin. Negative sign because the output signal in inverted.

Some theory needed to use op amp:

  • The formula: Vout = Ao(V+ – V-). This is for ideal op amp but the formula structure is the same for real life op amp, just that there will be some additional resistance components.
Vout for ideal op amp is

3 rules to note:

  • Rule 1: Ideal op amp, Ao = ∞ ———— Real life op amp Ao = 104 to 106
  • Rule 2 : Ideal op amp, Rin = ∞ ———— Real life op amp Rin = 106 Ω to 1012 Ω. Ideal op amp, Rout = 0 Ω ———— Real life op amp Rout = 10 Ω to 1000 Ω.
  • Rule 3: Ideal Op amp draws no current, true for real Op amp also (very small current: picoamps to nanoamps)