EED Lab Exp 3 Scalar, Summer and Voltage Follower.

EXPERIMENT-3

Aim:-

To study op-amp as a scalar, summerand voltage follower.

Sample Mannual                                    Detailed Mannual

Proteus Simulation:

Inverting Scalar                                Inverting Averaging                            Inverting Summer
Non Inverting Averaging                   Non Inverting Summer
Voltage Follower

Video of Simulation:

Inverting Scalar, Averaging & Summer                      Non-Inverting Averaging & Summer         Video Channel: E-Study

Components required:- 

Function generator, CRO, Regulated Power supply, 741 IC, connecting wires.

Theory:-

Operational amplifier is a direct-coupled high-gain amplifier usually consisting of one or more differential amplifiers and usually followed by a level translator and an output stage. The output stage is generally a push-pull or push-pull complementary symmetry pair. The operational amplifier is a versatile device that can be used to amplify DC as well as AC input signals and was originally designed for performing mathematical operations such as addition, subtraction, multiplication, and integration.

OP-AMP AS A SCALAR-

The op-amp may be used as an Adder or Scalar in both inverting as well as noninverting configuration figure 1 shows the inverting configuration with three inputs Input 1, Input 2 and Input 3. Depending on the relationship between the feedback resistor Rf and the input resistor Ra, Rb, and Rc, the circuit can be used as a summing amplifier (Adder) or a scaling amplifier.

If each input voltage is amplified by a different factor, in other words, weighted differently at the output, the circuit in figure 1 is then called a scaling or weighted amplifier. This condition can be accomplished if Ra, Rb, and Rc are different in values. Thus the output voltage of the scaling amplifier is :

Vout  =  - [(RF / Ra) Va + (RF / Rb) Vb + (Rf / Rc) Vc]

Where RF/Ra ≠  RF/Rb ≠ RF/Rc

OP-AMP AS A SUMMER-

The output voltage of a summing amplifier is proportional to the negative of the algebraic sum of its input voltages. Hence, the name summing amplifier. A summing amplifier is an inverted OP-Amp that can accept two or more inputs.

Fig. shows a three-input inverting summing amplifier.

Three voltages V₁, V₂ and V₃ are applied to the inputs and produce currents I₁, I₂ and I₃.

The inverting input of the OP-Amp is at virtual ground (0 V) and there is no current to the input.

So, the three input currents I₁, I₂ and I₃ combine at the summing point A and form the total current I_f which goes through R_f as shown in fig.1.

When all the three inputs are applied, the output voltage is

If R₁=R₂=R₃=R, then, we have,

Thus the output voltage is proportional to the algebraic sum of the input voltages.

If R_f =R1=R₂=R₃=R, then, we have

Thus, when the gain of summing amplifier is unity, the output voltage is the algebraic sum of the input voltages.

There are a number of applications of summing amplifiers. Here we will discuss the following two applications:

1.      As averaging amplifier

For averaging amplifier

R1=R2=R3=R

Rf/R =1/n

where n is number of inputs.

In that case the Vout = -1/n(V1+V2+V3)

2.      As Scaler amplifier

This condition can be accomplished if Ra, Rb, and Rc are different in values. Thus the output voltage of the scaling amplifier is :

Vout  =  - [(RF / Ra) Va + (RF / Rb) Vb + (Rf / Rc) Vc]

Where RF/Ra ≠  RF/Rb ≠ RF/Rc

OP-AMP AS A VOLTAGE FOLLOWER -

A unity gain buffer amplifier may be constructed by applying a full series negative feedback (Fig. 2) to an op-amp simply by connecting its output to its inverting input, and connecting the signal source to the non-inverting input (Fig. 3). In this configuration, the entire output voltage (β = 1 in Fig. 2) is placed contrary and in series with the input voltage. Thus the two voltages are subtracted according to KVL and their difference is applied to the op-amp differential input. This connection forces the op-amp to adjust its output voltage simply equal to the input voltage (V_out follows V_in )so the circuit is named op-amp voltage follower.

Used as a buffer amplifier to eliminate loading effects (e.g., connecting a device with a high source impedance to a device with a low input impedance).

Fig 2. Anegative feedback amplifier

Fig 3. Anop-amp–based unity gain buffer amplifier or op-amp as a VOLTAGE FOLLOWER

The importance of the circuit is due to the input and output impedances of the op-amp. The input impedance of the op-amp is very high, meaning that the input of the op-amp does not load down the source or draw any current from it. Because the output impedance of the op-amp is very low, it drives the load as if it were a perfect voltage source. Both the connections to and from the buffer are therefore bridging connections, which reduce power consumption in the source, distortion from overloading, crosstalk and other electromagnetic interference.

The voltage follower is often used for the construction of buffers for logic circuits.

 Observations:-

1.      Measure the value of Output Voltage it should be as per the operation.

2.      The input and output both are the dc signals.

3.      Observe outputs using different input voltages and wave type.

Result :-

The op-amp as a scalar, summer and voltage follower has been studied successfully.

Precautions:-

1.      Connections should be verified before clicking run button.

2.      The frequency should be in appropriate range for all voltage used so that the slew rate distortion does not affect the output.