ADDER AND SUBTRACTOR USING OPAMP
Aim :- To study the operational amplifier as a - (1) Summing (Adder) Amplifier, & (2) Difference (Subtractor) Amplifier.
Apparatus :-
Sr. Items No. Remarks
No. Required
1. Operational Amplifier 1 To perform experiment.
2. Power Supply 1 To Supply Power.
3. Digital Voltmeter 1 To measure Voltage.
Theory :- Operational Amplifier is used to amplified DC as well as AC input signals, and was designed for such mathematical functions like addition, subtraction, multiplication etc. with addition of suitable feedback components like resistors. Here we are using two functions of Operational Amplifier.
(1) Summing, (2) Subtracting.
(1) Summing (Adder) Amplifier :- In adder configuration, we are giving input to two terminals V1 and V2. So we get output at one terminal Vo. If we give supply to input terminals V1 and V2 by grounding the Non - Inverting terminal. So we get the summation of these two inputs at the output terminal due to the Summing Amplifier using Inverting Configuration. The following figure is of Summing Amplifier using Inverting Configuration.
The above figure shows two inputs Va and Vb. These two inputs depending on the relationship between the feedback resistor Rf and the input resistors Ra and Rb.
The function of the circuit can be verified by examine the operation for the output voltage Vo, which is obtained by Kirchhoff 's Current Law as under :
Ia + Ib = IB + If
Since Ri and A of the Operational Amplifier are ideally infinity. IB = 0 Amp. and Va = Vb = 0 volts.
Therefore,
V1 V2 Vo
Ra Rb Rf
Vo = Rf V1 Rf V2
Ra Rb
In the Circuit Ra = Rb = R, for example, the equation can be written as follows,
Vo = - Rf (V1 + V2)
R
This means that output voltage is equal to the negative sum of the all inputs. The gain of the circuit is Rf / R. Hence the circuit is called as Adder or Summing Amplifier. If the gain of the Circuit is 1 then,
Ra = Rb = Rf = R.
Thus,
Vo = - (V1 + V2).
(2) Subtractor Configuration :- For Subtractor amplifier differential configuration is used, because the differential amplifier amplifies the difference of the input. The Figure shows the Subtractor amplifier differential configuration as following.
A basic Differential Amplifier can be use as a Subtractor amplifier as shown in above figure.
From above figure the output voltage of the differential amplifier with a gain of 1 is,
Vo = - Rf (V1-V2) (Here, Rf = R).
R
Vo = V2 - V1.
It means that output voltage is the subtraction of the two input signals.
Procedure :-
(1) While operating Op. amp., first step is to set the null point. For this input is grounded and output is adjusted to zero.
(2) For adder configuration :-
(A) Input is given to the inverting terminal of opamp and Non Inverting terminal is grounded through ROM
Where, ROM = Rf R
Where, R = R1 R2
(B) Output is noted for various values of V1 and V2
(3) For Subtraction Configuration :-
(A) Input is given to inverting as well as Non inverting terminal. ROM is connected to Non Inverting Terminal.
(B) Output noted for various values of input voltages V1 and V2.
Conclusion :- With such op. amp., we can use as adder as well as subtractor configuration. In adder configuration we are giving input to V1 and V2, so we get Summation of this two inputs, at the output terminal with minus sign, the minus sign is because of we are doing this configuration in inverting configuration. While in subtractor configuration we are giving input to V1 and V2. So that at the output terminal, we get difference of these two inputs, because of Differential Configuration.