Operationamplifier

2. Operation Amplifier (op-amp)
 Operation Amplifier circuit designed to boost the
power of low level signal

3.  Op-amp are linier devise that have all the properties
required for nearly ideal DC amplification and are
therefore used extensively in signal conditioning,
filtering or to perform mathematical operation such as
add, subtract, integration and differentiation.

4. Ideal Op-Amp
 Ideal op-amp is basically a three terminal devise which
consists of 2 high impedance input, one called the
inverting input marked with a negative or minus sign
(-) and the other one called the non-inverting input
marked with positive or plus sign (+).
 The third terminal represents the op-amp output
which can both sink and source either a voltage or a
current

5. Block diagram of op-amp
+
-
Gain (A) RL
Rs
Vs
Amplifier loadSource
VL
VL = A. VsIdeally the output voltage is amplified version of the source or

6. From the source see an equivalent
resistance looking to the right or
can be drawn :
From the load see an equivalent
source looking to the left or can be
drawn :
Rs
+
-
Vs Rin
Vin VL
+
-
Rout
RL
A.Vin
Ideally Vin = Vs because Rin   Ideally VL = A.Vin because Rout  

8. Schematic symbol op - amp
There are : 2 input : inverting input (+) and non – inverting input
1 output
2 terminal for power supply (+ and -)

9. Ideal op-amp characteristic
 Rin =   Vin = VS
 Rout = 0  VL = A.Vin
 Open loop gain (A) = 
Open loop gain op-amp without positive or negative
feedback and for ideal amplifier the gain will be
infinite () but typical real value range from 20.000 to
200.000

10. Inverting Amplifier
 Inverting amplifier configuration :

11. Negative feedback
 Negative Feedback is the process of "feeding back" a fraction of the
output signal back to the input, but to make the feedback negative, we
must feed it back to the negative or "inverting input" terminal of the
op-amp using an external Feedback Resistor called Rƒ.
 This feedback connection between the output and the inverting input
terminal forces the differential input voltage towards zero
 This effect produces a closed loop circuit to the amplifier resulting in
the gain of the amplifier now being called its Closed-loop Gain
 This negative feedback results in the inverting input terminal having a
different signal on it than the actual input voltage as it will be the sum
of the input voltage plus the negative feedback voltage giving it the
label or term of a Summing Point.
 We must therefore separate the real input signal from the inverting
input by using an Input Resistor, Rin

12.  There are two very important rules to remember about
Inverting Amplifiers or any operational amplifier for that
matter and these are
1. No Current Flows into the Input Terminals
2. The Differential Input Voltage is Zero as V1 = V2 = 0
 Then by using these two rules we can derive the equation
for calculating the closed-loop gain of an inverting
amplifier, using first principles

13. Negative sign means inverting amplifier
Keep on your mind:
This amplification
process limited by
power supply voltage !

14. Transresistance Amplifier Circuit
 Another useful application of an inverting amplifier is
that of a "transresistance amplifier" circuit.
 A Transresistance Amplifier also known as a
"transimpedance amplifier", is basically a current-to-
voltage converter (Current "in" and Voltage "out").
 They can be used in low-power applications to convert
a very small current generated by a photo-diode or
photo-detecting device etc, into a usable output
voltage which is proportional to the input current as
shown

15. Transresistance Amp Configuration

16. Non – Inverting Amplifier
 In this configuration, the input voltage signal, ( Vin ) is
applied directly to the non-inverting ( + ) input
terminal which means that the output gain of the
amplifier becomes "Positive" in value in contrast to the
"Inverting Amplifier" circuit
 The result of this is that the output signal is "in-phase"
with the input signal

17. Non-inverting amplifier
configuration

18. Equivalent potential divider
network

19. Voltage Follower
 If we made the feedback resistor, Rƒ equal to zero,
(Rƒ = 0), and resistor R2 equal to infinity, (R2 = ∞),
then the circuit would have a fixed gain of "1" as all the
output voltage would be present on the inverting input
terminal (negative feedback).
 This would then produce a special type of the non-
inverting amplifier circuit called a Voltage Follower
or also called a "unity gain buffer"

20. Voltage Follower configuration

21. Summing Amplifier
 The Summing Amplifier is a very flexible circuit based
upon the standard Inverting Operational Amplifier
configuration that can be used for combining multiple
inputs
 previously in the inverting amplifier tutorial that the
inverting amplifier has a single input voltage, ( Vin )
applied to the inverting input terminal. If we add more
input resistors to the input, each equal in value to the
original input resistor, Rin we end up with another
operational amplifier circuit called a Summing Amplifier
"summing inverter" or even a "voltage adder”

22. Circuit of summing amplifier

23. Aplication for summing amplifier

25. Differential Amplifier
 If we connect signals to both of the inputs at the same time
producing another common type of operational amplifier
circuit called a Differential Amplifier.
 by connecting one voltage signal (V1) onto one input
terminal and another voltage signal (V2) onto the other
input terminal the resultant output voltage (Vout) will be
proportional to the "Difference" between the two input
voltage signals of V1 and V2 .
 Then differential amplifiers amplify the difference between
two voltages making this type of operational amplifier
circuit a Subtractor unlike a summing amplifier which
adds or sums together the input voltages. This type of
operational amplifier circuit is commonly known as a
Differential Amplifier configuration

26. Differential Amp Circuit

27.  If V1 = 0 then the op-amp became a non inverting amplifier. Vout for non inverting
amplifier is given as :
• If V2 = 0 then the op-amp function as inverting amplifier, Vout for inverting
amplifier is given as :
• The summing of Vout(a) and Vout(b) is given as :
• If R1 = R2 and R3 = R4 we find :

28. Aplication for differential amp:
 For bridge amplifier
• For automatic light switch

29. Op-amp integrator
 if we were to change the purely resistive ( Rƒ )
feedback element of an inverting amplifier to that of a
frequency dependant impedance, ( Z ) type complex
element, such as a Capacitor, (C) . What would be the
effect on the output voltage?.
 By replacing this feedback resistance with a capacitor
we now have an RC Network across the operational
amplifier producing an Op-amp Integrator

30. Simple Circuit diagram for op-amp integrator

31. Op-amp differentiator
 The basic Op-amp Differentiator circuit is the exact
opposite to that of the Integrator operational amplifier

32. Summary