741 Inverting Amplifiers

 

Aim: -To design and simulate Summing, Scaling and Averaging Amplifier circuits using 741.
Components: -

Name	EDWin Components Used	Description	Number of components required
RES	RC05	Resistor	6*
COMPARATOR	LM358	Op-amp	1
VDC	SMB_VDC	Dc voltage source	5
GND	SMB_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 push-pull or push-pull 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.

Figure shows the inverting configuration of 741 to implement the summing, scaling and averaging amplifiers. Depending on the relationship between the feedback resistor, R_F and the input resistors R_A, R_B and R_C the circuit can be used as a summing amplifier, a scaling amplifier or an averaging amplifier. The offset minimizing resistor R_OM is used to minimize the effect of input bias currents on the output-offset voltage The circuit functionality can be explained using the equation for output voltage obtained by applying Kirchoff’s current law at node A. Referring to the figure

since R_i and A of the op-amp are ideally infinity,

Summing Amplifier

If the resistor values in the above circuit are selected such that

Then equation 3 can be rewritten as

i.e., the output voltage is equal to the negative sum of all the input voltage times the gain of the circuit R_F/ R; hence the circuit is called a summing amplifier. When the gain of the circuit is 1,i.e, , the output voltage is equal to the negative sum of all the input voltages. Thus,

Scaling Amplifier

The circuit for summing amplifier can be converted to a scaling amplifier if each input voltage is amplified by a different factor i.e, weighted differently at the output. This condition can be accomplished if R_A, R_B and R_C are different in value. Thus the output voltage of the scaling amplifier is

Averaging Amplifier

The above circuit can be used as an averaging circuit in which the output of the circuit is equal to the average of all the input voltages. This is accomplished by using all resistors of equal value, . In addition, the gain by which each input is amplified must be equal to 1 over the number of inputs; that is,

where n is the number of inputs.

Thus for a circuit with 3 inputs, . Consequently from equation 3

Procedure: -

EDWin 2000 -> Schematic Editor:

The values are assigned for relevant components.

EDWin 2000 -> Mixed Mode Simulator:

Result: -

The output waveform may be observed in the waveform viewer. The output for Summing, Scaling and Averaging Amplifiers are shown below.

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. The circuit diagram is drawn by loading components from the library. Wiring and proper net assignment has been made.

741 Inverting Amplifiers

 

Aim: -To design and simulate Summing, Scaling and Averaging Amplifier circuits using 741.
Components: -

Name	EDWin Components Used	Description	Number of components required
RES	RC05	Resistor	6*
COMPARATOR	LM358	Op-amp	1
VDC	SMB_VDC	Dc voltage source	5
GND	SMB_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 push-pull or push-pull 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.

Figure shows the inverting configuration of 741 to implement the summing, scaling and averaging amplifiers. Depending on the relationship between the feedback resistor, R_F and the input resistors R_A, R_B and R_C the circuit can be used as a summing amplifier, a scaling amplifier or an averaging amplifier. The offset minimizing resistor R_OM is used to minimize the effect of input bias currents on the output-offset voltage The circuit functionality can be explained using the equation for output voltage obtained by applying Kirchoff’s current law at node A. Referring to the figure

since R_i and A of the op-amp are ideally infinity,

Summing Amplifier

If the resistor values in the above circuit are selected such that

Then equation 3 can be rewritten as

i.e., the output voltage is equal to the negative sum of all the input voltage times the gain of the circuit R_F/ R; hence the circuit is called a summing amplifier. When the gain of the circuit is 1,i.e, , the output voltage is equal to the negative sum of all the input voltages. Thus,

Scaling Amplifier

The circuit for summing amplifier can be converted to a scaling amplifier if each input voltage is amplified by a different factor i.e, weighted differently at the output. This condition can be accomplished if R_A, R_B and R_C are different in value. Thus the output voltage of the scaling amplifier is

Averaging Amplifier

The above circuit can be used as an averaging circuit in which the output of the circuit is equal to the average of all the input voltages. This is accomplished by using all resistors of equal value, . In addition, the gain by which each input is amplified must be equal to 1 over the number of inputs; that is,

where n is the number of inputs.

Thus for a circuit with 3 inputs, . Consequently from equation 3

Procedure: -

EDWin 2000 -> Schematic Editor:

The values are assigned for relevant components.

EDWin 2000 -> Mixed Mode Simulator:

Result: -

The output waveform may be observed in the waveform viewer. The output for Summing, Scaling and Averaging Amplifiers are shown below.

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. The circuit diagram is drawn by loading components from the library. Wiring and proper net assignment has been made.

741 Non-Inverting 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	SMB_VDC	Dc voltage source	5
GND	SMB_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 push-pull or push-pull 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 non-inverting mode. The circuit shown below is called a non-inverting amplifier since the input voltage sources and resistors are connected to the non-inverting terminal of the op-amp. The circuit can be used either as a summing or an averaging amplifier through the selection of appropriate values of resistors, R₁ and R_F. The input resistance R_iF of the non-inverting 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 V₁ at the non-inverting 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 non-inverting summing amplifier.

Averaging Amplifier

The output of the non-inverting 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 V₁ is the average of all the inputs.

Procedure: -

EDWin 2000 -> Schematic Editor:

The values are assigned for relevant components.

EDWin 2000 -> Mixed Mode Simulator:

Result: -

The output waveform may be observed in the waveform viewer.

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. The circuit diagram is drawn by loading components from the library. Wiring and proper net assignment has been made.