Operational Amplifier IC 741

• IC 741 is a monolithic IC, comprising of a general purpose Operational Amplifier.
• It has 7 functional pins, 4 pins capable of taking input and 1 pin for output . The Op-Amp is a 'Linear Amplifier' with an enormous variety of uses.
• The Op-Amp has inverting ( - ) and non-inverting (+) inputs, and an output at pin 6.
• In a circuit, the IC can be used in two ways.
• For inverting amplifier , the voltage goes into pin two.
• For non-inverting amplifier , the voltage goes into pin three.
• Here , we are going to see the use of Op - Amp as a summer and a subtractor.

Citation : From Opamp - Operational Amplifier By electroSome

Summing Amplifier

• The Summing Amplifier is a type of Op - Amp circuit configuration .
• It is used to add all the voltages present on two or more inputs to get a single summing output voltage.
• If we add more input resistors to the input, each equal in value to the original input resistor, (Rin) we end up with an operational amplifier circuit called a Summing Amplifier
• In this Summing Circuit, the output voltage, ( Vout ) now becomes proportional to the sum of the input voltages, V1, V2, V3, etc.
• The resistors could be chosen according to our design requirement of summing amplifier wherein the output is proportional to the amplified sum of all inputs.
• The current is calculated as , If = I1 + I2 + I3 = -[ V1/Rin + V2/Rin + V3/Rin ]

Citation : From Inverting and Non Inverting Summing Amplifier - Voltage Adder By Electronics Hub

Inverting Equation

• -Rf/ Rin ( Vin )
• => -Vout = Rf/Rin *V1 + Rf/Rin *V2 + Rf/Rin *V3

Summing Amplifier Equation :

• -Vout = Rf/ Rin (V1 + V2 + V3 + .. )
• If Rf = Rin, -Vout = (V1 + V2 = V3 + … )
• => Vout = -(V1 + V2 + V3 + … )

Applications Of Summing Amplifier

• Allows audio experts to combine signals from various channels.
• Every audio input can be configured independently without affecting the output.
• Used in digital to analog converter.

Advantages Of Summing Amplifier

• The summing point is virtually at earth potential .Hence , the signals from each different channel do not affect each other.
• Each channel can be summed or mixed regardless of the signal level and source impedance .

Disadvantages Of Summing Amplifier

• If you disconnect one of the inputs,it doubles the gain of the circuit for the remaining channel which is connected . But in inverting summing amplifier , it generates a virtual earth summing point

Differential Amplifier

Citation : From Differential Amplifier By Wikipedia

• The differential amplifier amplifies the difference in voltage , which is present on its inverting and non-inverting inputs.

• All Op-Amps are “Differential Amplifiers" , because of their input configuration.

• By connecting a voltage signal onto an input terminal and another voltage signal onto other input terminal , the resultant will be directly proportional to the difference between the two input voltages , V1 and V2.

• By connecting the inputs to make 0v ground, superposition can be used to solve for the output voltage Vout.

• The transfer function of a subtractor is given as:

• I1 = (V1 - Va) / R1 , I2 = (V2 - Vb) / R2 , If = (Va - Vout) / R3

• Summing point , Va = Vb and Vb = V2 * (R4) / (R2 + R4)

• If V2 = 0, then Vout(a) = -V1 * (R3/R1)

• If V1 = 0, then Vout(b) = V2 * (R4) / (R2 + R4) * (R1 + R3) / (R1)

• Vout = -Vout(a) + Vout(b)

Differential Amplifier Equation :

• Vout = R3/R1 * ( V2 - V1)
• If R3 = R1 , then Vout = V2 - V1

Applications Of Differential Amplifier

• Used in series negative feedback circuit.
• Used as a volume control circuit.
• Used as an automatic gain control circuit.

Advantages Of Differential Amplifier

• Manipulates differential signals.
• Provide immunity to external noise, a 6-dB increase in dynamic range, which gives a clear advantage for low-voltage systems .
• They reduce second-order harmonics.

Disadvantages Of Differential Amplifier

• Complexity is the main drawback of Differential Amplifier.
• To make a balanced differential amplifier,we need atleast two differential amplifiers , using a configuration known as a long-tailed pair.
• In practice, you need more components to further amplify the output,with provide biasing and so on.