ANADOLU UNIVERSITY
FACULTY OF ENGINEERING AND ARCHITECTURE
DEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
EEM 206 ELECTRICAL CIRCUITS LABORATORY
EXPERIMENT#4
OP-AMP CIRCUITS
1
OP-AMP CIRCUITS
The op-amp is a device that lends itself to construction of very good linear
amplifiers as well as many nonlinear circuits. The basic op-amp is a very-high-gain
voltage amplifier with two inputs. One input is called the noninverting input and is
indicated with a plus sign (+). The other input is called inverting input and is
indicated with a minus sign (-). The op-amp amplifies any difference in voltage that
appears between these two inputs and produces an output that is equal to this
difference multiplied by the open-loop gain of the op-amp.
V0 = A[V1 - V2]
(1)
Here V0 is an output voltage, A is the open-loop gain of op-amp, V1 is the
voltage on the noninverting input, V2 is the voltage on the inverting input. If both
inputs are at the same potential, the output is zero. Equation (1) is a standard algebraic
expression where V1 and V2 may be either + or - according to its polarity.
Figure 4.1: Op-amp circuit
Most op-amp circuits require a split power supply. A split power supply has
three terminals. One terminal is positive (+VCC) with respect to ground, and one
terminals is negative with respect to ground (-VEE). A third terminal, common, is
always connected to circuit ground. Most modern op-amp circuits require supply
voltages in the range of 3 to 15V, (+) and (-). You will be using (+) (-) 12V in most
of your experiments.
2
THE NONINVERTING OP-AMP CIRCUIT
Figure 4.2: Noninverting Amplifier Connection
The noninverting circuit uses a feedback path, such that the input to B is in
parallel with the output of the op-amp and the output from B is series with the input of
the op-amp. A fraction of the output voltage is fed back in series with the incoming
signal, so that the sum (Ve) is almost zero.
Vf is the voltage across R2. Since Ve is very small, Vin is approximately equal
to Vf . The value of Vf is found by using the voltage divider rule from elementary
circuit analysis:
Vf = Vo.[R2/(R1+R2)]
(2)
Voltage gain: Av = (Vo/Vin) = (R1/R2) +1.
The Inverting Op-amp Circuit
Figure 4.3: Inverting Amplifier
This circuit produces an amplified, inverted (negative) version of Vin. R2
provides negative feedback connection of the inverting amplifier. In Fig.4.3, the
current Iin flowing through R1 creates a voltage drop. The left hand side of R1 is at
almost zero volts, therefore:
Vo = - IinR1
(3)
3
Since Iin = Vin/R2 the voltage gain is found to be:
Av = - ( R1 / R2 )
(4)
The Voltage Follower
Figure 4.4: Voltage Follower
Vin = Vo, Av = 1
(5)
The Summing Amplifier
Figure 4.5: Summing Amplifier
If we replace the single input of the inverting amplifier of Fig 4.3 with
multiple inputs, we obtain the circuit which is known as “summing amplifier”. Each
input will produce a component of the output voltage as though it was the only input.
Vo = - [V1x (Rf / R1) + V2x(Rf / R2) + V3x(Rf / R3) + V4x(Rf / R4)]
= - Rf x [ (V1 / R1) + (V2 / R2 ) + (V3 / R3) + (V4 / R4)]
(6)
4
EXPERIMENTAL WORK
Experiment I :
Schematic Diagram Of Circuit:
Materials Required:
1)
2)
3)
4)
5)
1x 741CP op-amp,
2 x 10 KΩ resistor, 1x1 KΩ resistor, 1x100 KΩ potentiometer
Dual channel oscilloscope,
Function generator,
DC power supply, board and cables.
Calculations:
Find the voltage gain of this circuit for the case:
a) R2 = 1KΩ
b) R2 = 10 KΩ
R1 = 10KΩ
Procedure:
1. For R2 = 1KΩ, build the circuit and be careful to connec the signal generator,
oscilloscope, and circuit grounds all together. Vin is obtained from the wiper
arm of a 100 KΩ potentiometer (R0).
2. Adjust the function generator for an output of sin2000πt V.
3. Adjust the 100 K potentiometer (R0) to supply a voltage of 0.5sin2000πt V.
Use the DC power supply to obtain ± 12 Vdc supply voltage for the opamp
4. For R2 = 10KΩ repeat the procedure for steps1-4 above.
5
R2
Vo
V in
Vo/Vin
(R1/R2) + 1
Experiment II :
Schematic Diagram Of Circuit:
Materials Required:
1)
2)
3)
4)
5)
1x 741CP op-amp,
1 x 100 KΩ resistors, 1x1 MΩ resistor, 1x100 KΩ potentiometer
Dual channel oscilloscope,
Function generator,
DC power supply, board and cables.
Calculations:
a) Find Vi’.
b) Find the voltage gain of this circuit
Procedure:
1. Build the circuit following the precautions of previous experiments.
2. Adjust the function generator for an output of sin2000πt V.
3. Adjust the 100 KΩ potentiometer to supply a voltage of 0.5sin2000πt V.
Use the DC power supply to obtain ± 12 Vdc supply voltage for the opamp
Record your readings:
Vi = .............................
Vi’ = .............................
Vo = ............................
Vo /Vi = ........................
6
R1/R2 = .........................
Experiment III :
Schematic Diagram Of Circuit:
Materials Required:
1)
2)
3)
4)
5)
1x 741CP op-amp,
1x100 KΩ KΩ potentiometer,
Dual channel oscilloscope,
Function generator,
DC power supply, board and cables.
Calculations:
Find the voltage gain of this circuit
Procedure:
1. Apply power to the circuit and adjust the wiper arm of 100 KΩ pot to provide
a voltage of sin2000πt V at the noninverting input.
2. Use the DC power supply to obtain ± 12 Vdc supply voltage for the opamp.
3. Measure the output voltage and find the gain.
7
Experiment IV :
Schematic Diagram Of Circuit:
Materials Required:
1)
2)
3)
4)
5)
1x 741CP op-amp,
3x100 KΩ resistor,
Dual channel oscilloscope,
Function generator,
DC power supply, board and cables.
Calculations:
Find Vo for the case V1 = 5 Vdc V2 = 2sin2000πt V
Procedure:
1. Use the DC power supply to obtain V1= 5 Vdc and ± 12 Vdc supply voltage
for the opamp.
2. Use the function generator for V2 = 2sin2000πt V.
3. Measure Vo and write down its expression:
Vo = .............................................................
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