126 Basic Electronics
Introduction
Operational amplifier is an high gain direct coupled differential amplifier which is used
to perform mathematical operations such as addition, subtraction, multiplication, division,
differentiation etc. and it is used to amplify both AC and DC signals.
Operational amplifiers are available in IC packages of single, dual or quad op-amp within
one single device. The most commonly used among all operational amplifiers in electronic
kits, projects is the industry standard µA741.
4.1 Block Diagram of Stages inside Op-amp
V1(t) Intermediate Buffered level Vo
Input Stage Output Stage
V2(t) Stage shifting
Figure 4.1.1: Internal circuit block diagram of op-amp
The block diagram of op-amp consist of input stage, intermediate stage, buffer and
level shifting stage and output stage. Figure 4.1.1 shows the internal circuit Block diagram
of op-amp.
Input stage: It consists of dual input, balanced output differential amplifier. Its function is
to amplify the difference between two input signals. It provides high differential gain, high
input impedance and low output impedance.
Intermediate stage: It consist of dual input unbalanced output differential amplifier. The
overall gain requirement of an op-amp is very high since input stage alone cannot provide
such a high voltage gain intermediate stage is used to provide the required additional
voltage gain.
Buffer and Level shifting stage: The op-amp amplifies a dc signal also the small dc voltage
level of the previous stage may get amplified and applied to the input of the next stage
causing distortion in the output. Hence the level shifting stage is used to bring the dc level
to ground potential.
Output stage: It consists of push pull complimentary amplifier which provides large AC
Output voltage with a low output impedance.
4.2 Op-amp Symbols
Op-amps can be connected into two basic configuration Inverting and non-inverting. Figure 4.2.1
shows the symbol of op-amp and pin details of commonly used IC741 is shown in Figure 4.2.2.
Inverting op-amp voltage: Vi is applied to the inverting terminal keeping the
non-inverting terminal of the op-amp at ground point then the output voltage will be 180° out of
phase w.r.t input signal applied as shown in Figure 4.2.3(b). Figure 4.2.3(a) shows the inverting
operational amplifier.
,Operational Amplifier and Applications 127
+VCC(+Vsat)
Offset Null 1 μ 8 NC
Inverting
– Output A
terminal Inverting input 2 7 +VCC supply
Op-amp 7
Non-inverting Non-inverting
terminal + 3 4 6 output
input
–VCC 4 1 5 Offset Null
supply
–VEE(–Vsat)
Figure 4.2.1: Op-amp symbol Figure 4.2.2: Pin details of µA741 IC
Vi
+VCC
t
Vi –
Op-amp Vo Vo
+
t
–VEE
Figure 4.2.3(a): Inverting op-amp Figure 4.2.3(b): Input and output waveforms
of Inverting op-amp
Non-inverting op-amp: The voltage Vi is applied to non-inverting input Keeping
inverting input to a ground point then the output voltage will be in phase with input signal
applied. i.e. the phase difference between input signal and output signal is 0° as shown in
Figure 4.2.4(b). Figure 4.2.4(a) shows Non-inverting op-amp.
Vi
+VCC
t
–
op-amp Vo Vo
Vi +
t
–VEE
Figure 4.2.4(a): Non-inverting op-amp Figure 4.2.4(b): Input and output
waveforms of Non-inverting op-amp
, 128 Basic Electronics
4.3 Ideal Operational Amplifier
Figure 4.3.1 shows ideal opearational amplifier circuit and Figure 4.3.2 shows symbolic
representation of circuit. In ideal differential amplifier, the circuit consists of two transistors
connected back to back. If two inputs are given to a base of each transistors and output is
taken between 2 collectors of the two transistors then Vo = A(V2 – V1), where A is open
loop gain of op-amp. V1, V2 are inputs of op-amp. If two voltages V1 and V2 are applied to
an op-amp then output of the op-amp will be Vo = A (V2 – V1) where, A is the gain of the
op-amp. +VCC
Rc Rc
Vo
– +
Rb Rb
V1 V2
RE
Figure 4.3.1: Ideal operational amplifier circuit
+VCC
V1 V1 –
Ideal
Vo Op-amp Vo
V2 op-amp V2 +
–VEE
(a): Block diagram (b): Symbol
Figure 4.3.2: Schematic representation of op-amp circuit
+VCC
V1 –
Op-amp Vo
V2 +
–VEE
Figure 4.3.3: Difference amplifier
Introduction
Operational amplifier is an high gain direct coupled differential amplifier which is used
to perform mathematical operations such as addition, subtraction, multiplication, division,
differentiation etc. and it is used to amplify both AC and DC signals.
Operational amplifiers are available in IC packages of single, dual or quad op-amp within
one single device. The most commonly used among all operational amplifiers in electronic
kits, projects is the industry standard µA741.
4.1 Block Diagram of Stages inside Op-amp
V1(t) Intermediate Buffered level Vo
Input Stage Output Stage
V2(t) Stage shifting
Figure 4.1.1: Internal circuit block diagram of op-amp
The block diagram of op-amp consist of input stage, intermediate stage, buffer and
level shifting stage and output stage. Figure 4.1.1 shows the internal circuit Block diagram
of op-amp.
Input stage: It consists of dual input, balanced output differential amplifier. Its function is
to amplify the difference between two input signals. It provides high differential gain, high
input impedance and low output impedance.
Intermediate stage: It consist of dual input unbalanced output differential amplifier. The
overall gain requirement of an op-amp is very high since input stage alone cannot provide
such a high voltage gain intermediate stage is used to provide the required additional
voltage gain.
Buffer and Level shifting stage: The op-amp amplifies a dc signal also the small dc voltage
level of the previous stage may get amplified and applied to the input of the next stage
causing distortion in the output. Hence the level shifting stage is used to bring the dc level
to ground potential.
Output stage: It consists of push pull complimentary amplifier which provides large AC
Output voltage with a low output impedance.
4.2 Op-amp Symbols
Op-amps can be connected into two basic configuration Inverting and non-inverting. Figure 4.2.1
shows the symbol of op-amp and pin details of commonly used IC741 is shown in Figure 4.2.2.
Inverting op-amp voltage: Vi is applied to the inverting terminal keeping the
non-inverting terminal of the op-amp at ground point then the output voltage will be 180° out of
phase w.r.t input signal applied as shown in Figure 4.2.3(b). Figure 4.2.3(a) shows the inverting
operational amplifier.
,Operational Amplifier and Applications 127
+VCC(+Vsat)
Offset Null 1 μ 8 NC
Inverting
– Output A
terminal Inverting input 2 7 +VCC supply
Op-amp 7
Non-inverting Non-inverting
terminal + 3 4 6 output
input
–VCC 4 1 5 Offset Null
supply
–VEE(–Vsat)
Figure 4.2.1: Op-amp symbol Figure 4.2.2: Pin details of µA741 IC
Vi
+VCC
t
Vi –
Op-amp Vo Vo
+
t
–VEE
Figure 4.2.3(a): Inverting op-amp Figure 4.2.3(b): Input and output waveforms
of Inverting op-amp
Non-inverting op-amp: The voltage Vi is applied to non-inverting input Keeping
inverting input to a ground point then the output voltage will be in phase with input signal
applied. i.e. the phase difference between input signal and output signal is 0° as shown in
Figure 4.2.4(b). Figure 4.2.4(a) shows Non-inverting op-amp.
Vi
+VCC
t
–
op-amp Vo Vo
Vi +
t
–VEE
Figure 4.2.4(a): Non-inverting op-amp Figure 4.2.4(b): Input and output
waveforms of Non-inverting op-amp
, 128 Basic Electronics
4.3 Ideal Operational Amplifier
Figure 4.3.1 shows ideal opearational amplifier circuit and Figure 4.3.2 shows symbolic
representation of circuit. In ideal differential amplifier, the circuit consists of two transistors
connected back to back. If two inputs are given to a base of each transistors and output is
taken between 2 collectors of the two transistors then Vo = A(V2 – V1), where A is open
loop gain of op-amp. V1, V2 are inputs of op-amp. If two voltages V1 and V2 are applied to
an op-amp then output of the op-amp will be Vo = A (V2 – V1) where, A is the gain of the
op-amp. +VCC
Rc Rc
Vo
– +
Rb Rb
V1 V2
RE
Figure 4.3.1: Ideal operational amplifier circuit
+VCC
V1 V1 –
Ideal
Vo Op-amp Vo
V2 op-amp V2 +
–VEE
(a): Block diagram (b): Symbol
Figure 4.3.2: Schematic representation of op-amp circuit
+VCC
V1 –
Op-amp Vo
V2 +
–VEE
Figure 4.3.3: Difference amplifier
