2. An operational amplifier (Op-Amp) is a differential amplifier
that amplifies the difference of voltages applied to its two
input terminals (differential input), and provides a single-
ended output.
The basic circuit of op-amp IC 741

3. IC Op-amp comes so close to ideal performance that it is useful to state the characteristics of an
ideal amplifier without regard to what is inside the package.
1.Infinite voltage gain
2.Infinite input impedance
3.Zero output impedance
4.Infinite bandwidth
5.Zero input offset voltage (i.e., exactly zero out if zero in).
These characteristics lead to the golden
rules for op-amps. They allow you to logically
deduce the operation of any op-amp circuit.

4. • Inverting amplifier
• Non-inverting amplifier
• Summing amplifier
• Substractor
• Differentiation
• Integrator
• Comparator

5. Opposite is a diagram of an INVERTING
AMPLIFIER. This means that if the voltage
going into the 741 chip is positive, it is negative
when it comes out of the 741. In other words it
reverses polarity (inverts polarity).
Two resistors are needed to make the 741
work as an amplifier, R1 and R2. In most text
books diagrams like this are used to represent
the 741.
GAIN (AV) = -R2 / R1
Example : if R2 is 100 kilo-ohm and R1 is 10
kilo-ohm the gain would be :
-100 / 10 = -10 (Gain AV)
If the input voltage is 0.5v the output voltage
would be :
0.5v X -10 = -5v

6. In this circuit the signal is applied to the non-
inverting input of the op-amp. However the
feedback is taken from the output of the op-
amp via a resistor to the inverting input of the
operational amplifier where another resistor is
taken to ground. It is the value of these two
resistors that govern the gain of the
operational amplifier circuit.
Av = 1 + R2 / R1

7. The summing amplifier is a handy circuit enabling you to add several
signals together. What are some examples? If you're measuring
temperature, you can add a negative offset to make the display read "0"
at the freezing point. On a precision amplifier, you may need to add a
small voltage to cancel the offset error of the op amp itself. An audio
mixer is another good example of adding waveforms (sounds) from
different channels (vocals, instruments) together before sending the
combined signal to a recorder.
Vo = - RF ( V1 / R1 + V2 / R2 + V3 / R3)
= - ( V1 · RF / R1 + V2 · RF / R2 + V3 · RF / R3 )

8. The Subtractor also called a difference amplifier, uses both the inverting and non-inverting
inputs to produce an output signal which is proportional to the difference between the
two input voltages V1 and V2. More inputs can be subtracted. Resistances are equal (R = R
and RA = RA) then the output voltage is as given and the gain is +1. If the input resistance
are unequal the circuit becomes a differential amplifier.

9. The right-hand side of the capacitor is held to a voltage of 0 volts, due to
the "virtual ground" effect. Therefore, current "through" the capacitor is
solely due to change in the input voltage. A steady input voltage won't
cause a current through C, but a changing input voltage will.

10. Continue…
Capacitor current moves through the feedback resistor, producing a drop
across it, which is the same as the output voltage. A linear, positive rate of
input voltage change will result in a steady negative voltage at the output of
the op-amp. Conversely, a linear, negative rate of input voltage change will
result in a steady positive voltage at the output of the op-amp. This polarity
inversion from input to output is due to the fact that the input signal is being
sent (essentially) to the inverting input of the op-amp, so it acts like the
inverting amplifier mentioned previously. The faster the rate of voltage change
at the input (either positive or negative), the greater the voltage at the output.
The formula for determining voltage output for the differentiator is as follows:

11. As before, the negative feedback of the op-amp ensures that the inverting
input will be held at 0 volts (the virtual ground). If the input voltage is exactly
0 volts, there will be no current through the resistor, therefore no charging of
the capacitor, and therefore the output voltage will not change. We cannot
guarantee what voltage will be at the output with respect to ground in this
condition, but we can say that the output voltage will be constant.

12. The Comparator has many uses but the most common is to compare the input voltage to
a reference voltage and switch the output if the input voltage is above the reference
voltage. If the input goes more positive than the reference voltage set by the voltage
divider, Vin > Vref, the output changes state. When the input voltage drops below the
preset reference voltage and Vin < Vref, the output switches back. By using negative
feedback the comparator can be converted into a Schmitt Trigger circuit.
Here are just some of the more common operational amplifier building block
configurations used in electronic circuits. All the above circuits can be constructed
using a variety of different op-amps including the famous 741 op-amp.