741 NonInverting Amplifiers
Aim
To design and simulate Summing and Averaging Amplifier circuits using
741.
Components
Name

EDWin Components Used 
Description 
Number of components
required 
RES 
RC05 
Resistor 
6 
COMPARATOR 
LM358 
Comparator 
1 
VDC 
VDC 
Dc voltage source 
5 
GND 
SPL0 
Ground 
7* 
Theory
An operational amplifier is a direct coupled
high gain amplifier consisting of one or more differential amplifiers and usually followed
by a level translator and an output stage which is
usually a pushpull or pushpull complementary symmetry pair. An operational amplifier can be used to
amplify ac as well as dc input signals and was originally designed
for computing such mathematical functions as addition, subtraction, multiplication
and integration.
An opamp can be configured in
either the inverting or in the noninverting mode. The circuit shown
below is called a noninverting amplifier, since the
input voltage sources and resistors are connected to the noninverting terminal of the
opamp. The circuit can be used either as a summing or an
averaging amplifier through the selection of appropriate values of resistors, R_{1}
and R_{F}. The input resistance R_{iF} of the noninverting amplifier is very large and is given
by
In order to verify the
functions of the circuit, the expression for the output voltage can be
obtained as follows. Applying the superposition theorem,
the voltage
V_{1} at
the noninverting terminal is
Hence the output voltage V_{o} is
Summing Amplifier
The Summing Amplifier produced using 741 is the circuit that sums up
all the input voltages. As evident from equation 4 if the gain is equal to the number of inputs, the output voltage becomes equal to the sum of all input
voltages. That is, if , then .
Hence the circuit is called a noninverting summing amplifier.
Averaging Amplifier
The output of the noninverting amplifier as obtained from
equation 4 is equal to the average of all the input voltages times the
gain of the circuit, hence the name averaging amplifier. Depending
on the application requirement the gain can be set to a specific value. If the gain is 1 then the output voltage will be equal to
the average of all input voltages. One special feature to be noted is that
the non
inverting input voltage V_{1} is the
average of all the inputs.
Procedure
EDWinXP> Schematic Editor: The circuit diagram is drawn by loading components
from the library. Wiring and proper net assignment has been made.
The values are assigned for relevant components.
EDWinXP> Mixed Mode Simulator: The circuit is preprocessed. Waveform markers are placed in
input and output of the circuit. GND net is set as reference net. The Transient Analysis parameters have been
set. The Transient Analysis is executed and output waveform is observed in
the Waveform Viewer.
Result
The output waveform may be observed in the waveform viewer.