I.D. No.
Student Signature of the
Name Instructor with
Batch No. Date
Day & Date
Experiment 1
Characterization of Op-amp
Objective:
To study
1. The input offset voltage
2. The input bias and offset current
3. Open loop gain
4. Slew rate
Components required:
IC 741, 10 k Potentiometer, Resistors – 10,100,1k,1.5K,5.6k,10k,100k,and
1M .
Experiment:
1. Input offset voltage
1.1 Assemble the circuit as shown in Figure 1, with R1= 100 and R2= 1k.
Observe the dc output voltage. Calculate the input offset voltage which is given
by Vos=Vo R1/(R1+R2)
Draw the circuit of Fig6.3 of TB2 Page No. 43
R2 in Vo in V Vos=Vo R1/(R1+R2) in
V
1k
10k
100k
1
1.2 From the data sheet of 741 op-amp, find the maximum value of input bias
current, IBmax. Calculate the input offset voltage, which is given by IBmax
R1.
IBmax=…………….. Input offset voltage
1.3 Compare the results of step (i) and (ii).
Parameter From step From step 1.2
1.1
Vos
1.4 Connect the fixed terminals of a 10 k potentiometer (nulling potentiometer)
between pins 1 and 5 of the op-amp and the variable terminal to the
negative power supply voltage, -15 V. Change the knob of the
potentiometer to make the output zero. This nulls the effect of input
offset voltage.
2
2. Input Bias current and input offset currents:
2.1 Assemble the voltage follower circuit as shown in Figure 2. Connect the
non- inverting input to ground. Using a nulling potentiometer, make the
output zero for zero input as per procedure 1.4.
Draw the circuit of Fig6.4 of TB2 Page No. 44
2.2 Connect a resistor R1 of value 1 M between the non-inverting input and
ground. Measure the output voltage Vo2. Calculate the current IB2, given by
IB2=Vo2/R1.
Vo2 =………………..
IB2=Vo2/R1=……………..
2.3 Remove the resistor R1 and ground the non-inverting input. Now connect
resistor R1 of value 1M between the inverting input and output. Measure the
output voltage Vo1. Calculate the current IB1, given by IB1=Vo1/R1.
Vo1 =………………..
IB1=Vo1/R1=……………..
2.4 Calculate the input bias current and the input offset current from these two
values.
2.5 Compare the results with the data sheet values.
3
Parameter From step 2.4 From Data Sheet
Input bias current
Input offset current
3. Open-loop gain
3.1 Assemble the circuit as shown in Figure 3. Given R1=1.5 k, R2= 5.6 k,
R3= 10 k and R4= 10.
Draw the circuit of Fig6.6 of TB2 Page No. 45
3.2 Connect a dc source at the input Vs, and adjust its value so that the output
is equal to -10V. Measure V1.
V1 =……………V
3.3 Calculate the differential input voltage Vdiff=VII – VNII= V1/1000
3.4 Calculate the open-loop gain, A=V0/Vdiff.
4
4. Slew Rate
4.1 Assemble the voltage follower circuit.
4.2 Apply 10Vp-p, 10 kHz square wave input, Vs.
4.3 Measure the rise time of the output waveform and calculate the slew rate.
4.4 Assemble a inverting amplifier circuit with a gain of 1, by selecting
R1=RF=10 k. Repeat steps 4.2 and 4.3.
4.5 Compare the two values.
Draw the circuit of voltage follower and inverting amplifier
Circuit Rise time V0p-p in Volts Slew Rate=V0p-p/rise time
Voltage follower
Inverting
Amplifier
5 PSPICE Simulations:
Use the macro model A 741 and connect a load resistor of 10 k and power
supply voltages of 15 V.
5.1 Simulate the circuit as used in experiment 1.1 using PSPICE. Do the dc
analysis to print the values of the output voltage. Calculate the input offset
voltage. Compare the results with the experimental results.
5.2 Simulate the circuit, as used in experiment steps 2.1 through 2.3, using
PSPICE. Do the dc analysis to print the values of the output voltage.
Calculate the input bias and offset currents. Compare the results with the
experimental results.
5.3 Simulate the circuit, as used in experiment steps 3.1 through 3.2, using
PSPICE. Compare the results with the experimental results.
