Lab 1
Applications of Operational Amplifier
Objective
To demonstrate the use of op-amp as:
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Summing amplifier
Subtractor
Integrator
Differentiator
Theory
Summing Amplifier
Op-amp may be used to perform summing operation of several input signals in inverting in
inverting and non-inverting mode. The input signals to be summed up are given to inverting
terminal or non-inverting terminal through the input resistance to perform inverting and noninverting summing operations respectively.
Subtractor
The basic difference amplifier can be used as a Subtractor. The signals to be subtracted are
connected to opposite polarity inputs i.e. in inverting or non-inverting terminals of the op-amp.
Integrator
Integrator is used to integrate the input waveform:
𝑉𝑜 = ∫
𝑉𝑖𝑛 𝑑𝑡
Here in the inverting amplifier configuration, the feedback resistor Rf is replaced by capacitor.
Integrators are commonly used in wave shaping signal generators etc. For proper wave
integration, T >> RC. Gain and linearity of the o/p are two advantages of op-amp integrators.
Linearity is due to linear charging of capacitor. Its limitation is for Vin =0 and for low frequencies,
XC =∞ or the capacitor C acts as an open circuit. Therefore, the op-amp integrator works as an
open loop amplifier and the gain becomes infinity or very high.
Differentiator
Here the output waveform is the derivative of the input waveform. In a basic inverting amplifier,
if R1 is replaced by C1, we get the differentiator. But at high frequencies, the gain of the circuit
(Rf/XC1) increases with increase in frequency at the rate of 20dB/decade. This makes the circuit
unstable. Also XC1 decreases when frequency increases.
Equipment
● DC power supply
● Function generator
● Oscilloscope
● Breadboard
● Operational amplifier, 741 or equivalent
● Resistors: 1kΩ, 10kΩ
● Capacitors: 0.01μF, 0.47μF
Integrator
Figure 1: Schematic of the Integrator
Procedure
● Construct the circuit in Figure 1.
● Apply DC power to your circuit. Set the function generator to provide a square wave
signal of 2Vp-p at 10 kHz.
● Connect your oscilloscope to monitor both the input and output signals. The output of
the integrator is given by:
𝑡
𝑑𝑡
𝑉𝑜𝑢𝑡 = − ∫ 𝑉𝑖𝑛
𝑅. 𝐶
0
● Sketch the oscilloscope display in Graph 4.2, noting the peak values of the signals.
Note: As long as the input signal is a constant value, either positive or negative, the output of the
integrator will be a voltage increasing at a rate determined by R1C1 in the opposite polarity of
Vin.
Possible Output
Figure 2: Possible Output for Integrator
Observations
Integrator Input/output for square wave:
Differentiator
Figure 3: Schematic of the Differentiator
Procedure
● Construct the circuit of differentiator as in Figure 3.
● Connect your function generator set to square wave output and adjust to 2Vp-p at 1 kHz.
Apply DC power to the circuit.
● Connect your oscilloscope in dual-trace mode to monitor both Vin and Vout. Observe the
signal waveforms. The output of the differentiator is given by:
𝑉𝑜𝑢𝑡 = −𝑅𝑓 𝐶
𝑑𝑉𝑖𝑛
𝑑𝑡
● Notice that at the leading and trailing edges of the input signal there is an output from
the differentiator. Also when the input is constant, even though it is not zero, there is no
output.
● Sketch the oscilloscope display in Graph 4.3, noting the peak values of the signals.
● Switch the function generator to obtain a triangular waveform of 2Vp-p at 1 kHz. Observe
the oscilloscope display. Notice that as long as the input signal is changing at a fixed rate,
the output is a nearly constant value. Sketch the oscilloscope display in Graph 4.4, noting
the signal peak values.
● To illustrate the differentiator function, set your function generator to obtain a sine wave
output of 2Vp-p at 1kHz. Notice that your output is also a sinusoidal waveform. It is,
however, phase shifted by 90 degrees to the input. This is a cosine wave, since the
derivative of the sine is the cosine.
Possible Output
In case of square wave differentiator shows following output:
Figure 4: Possible Output for Differentiator
Observations
Differentiator Input/output for square wave:
Differentiator Input/output for sine wave:
Summing Amplifier
Figure 5: Summing Amplifier
Procedure
● Connect the circuit as shown in Figure 5.
● Connect batteries for voltage V1, V2.
● Measure and note the output voltage and compare it with theoretical value:
𝑉0 = −(
𝑅𝑓
)(𝑉 + 𝑉2 )
𝑅𝑖 1
GAIN =0.5
Observations
V1
V2
Theoretical
V0
12V
-5V
3.55V
12
12
12V
Table 1: Summing Amplifier
Practical
V0
Subtractor
Figure 6: Subtractor
Procedure
● Connect the circuit as shown in Figure 6.
● Measure and note the output voltage and compare it with theoretical value.
𝑅𝑓
𝑉0 = ( )(𝑉2 − 𝑉1 )
𝑅1
Observations
V1
V2
Theoretical
V0
-5
-12
Practical
V0
8
12
-12
24
Table 2: Subtractor