Study of Opamp as summing & difference amplifier

The Summing Amplifier

Object:-  Design the circuit diagram. Determine the theoretical output voltage of summing amplifier. Take the practical output voltage reading.

Required Equipment :-  Multimeter, CRO, CDS, Power Supply ±15V  for Opamp

Components required:- Op Amp (Ic741) – 1No  2)Resistors Rin=1k-2nos ,  Rf= 1K

Theory - The Summing Amplifier is a very flexible circuit based upon the standard Inverting Operational Amplifier configuration. As its name suggests, the “summing amplifier” can be used for combining the voltage present on multiple inputs into a single output voltage.

Summing Amplifier Circuit

Procedure:- Connect the circuit as given above. Take care to connect  power supply to the Opamp.  All power supply grounds should be common. Take V1=2v, V2=3v and V3=5v dc voltage. Take the output at pin no. 6.

The output voltage, ( Vout ) now becomes proportional to the sum of the input voltages, V1, V2, V3 etc. Then we can modify the original equation for the inverting amplifier to take account of these new inputs thus:

Summing Amplifier Equation

Measure the output voltage at pin  no. 6  and verify 

Difference  Amplifier

Object :- 1)Design the circuit diagram. 2)Determine the theoretical output voltage of differential amplifier.  3)Take  the practical output voltage reading.

Required Equipment :- 1) Multimeter 2)CRO 3)CDS 4)Power Supply ±15V for opamp

Components required 1)   Op Amp (Ic741) – 1No 2)Resistors R1,R2=1k,  R3, R4=3.3K

Thus far we have used only one of the operational amplifiers inputs to connect to the amplifier, using either the “inverting” or the “non-inverting” input terminal to amplify a single input signal with the other input being connected to ground. But we can also connect signals to both of the inputs at the same time producing another common type of operational amplifier circuit called a difference  Amplifier.

Then difference amplifiers amplify the difference between two voltages making this type of operational amplifier circuit a Subtractor unlike a summing amplifier which adds or sums together the input voltages. This type of operational amplifier circuit is commonly known as a difference Amplifier configuration and is shown below:

Difference Amplifier Equation

 

If all the resistors are all of the same ohmic value, that is: R1 = R2 = R3 = R4 then the circuit will become a Unity Gain Differential Amplifier and the voltage gain of the amplifier will be exactly one or unity. Then the output expression would simply be Vout = V2 - V1. Also note that if input V1 is higher than input V2 the output voltage sum will be negative, and if V2 is higher than V1, the output voltage sum will be positive.

Measure the output voltage at pin  no. 6  and verify