In this tutorial I will explain you the working of an operation amplifier. Both inverting and non-inverting amplifiers are explained and simulated using PSPICE. At the start a brief and concise introduction of inverting and non-inverting amplifiers is provided with the explanation of the output they will show. After that both the circuits are simulated using PSPICE and the result are compared with the theoretical discussion provided (which should be same). At the end of the tutorial you are provided with an exercise to do it by yourself, and in the next tutorials I will assume that you have done those exercises and I will not explain the concept regarding them
Introduction to inverting and non-Inverting amplifiers
Amplifier as the named implies are used for the amplification of a signal. The signal can be amplified either in positive direction or in negative direction. Two types of amplifiers are very common in electronics i.e.
- Inverting amplifier
- Non-inverting amplifier
Inverting amplifier simulation PSPICE
An inverting amplifier is one which the output is given as feedback to the negative terminal of the operation amplifier. The output of the inverting amplifier is the inverted form of the input signal as the name implies multiplied by the gain factor and is 180 degrees out of phase in case of sinusoidal input. A simple circuit diagram of an inverting amplifier is shown in the figure below,
Figure 1: Inverting amplifier
The output of an inverting amplifier is given in the figure below,
Figure 2: Output of inverting amplifier
And the formula to calculate the gain of an inverting amplifier is
Non-Inverting amplifier Simulation PSPICE
A non-inverting amplifier is one which the output is given as feedback to the negative terminal of the operation amplifier, however the input is supplied through the positive terminal. The output of the inverting amplifier is same as the input signal multiplied by the gain factor and is in phase in case of sinusoidal input. A simple circuit diagram of an non-inverting amplifier is shown in the figure below,
Figure 1: Inverting amplifier
The output of a non-inverting amplifier is given in the figure below,
Figure 2: Output of non-inverting amplifier
And the formula to calculate the gain of a non-inverting amplifier is
Explanation with example of simulation in PSPICE
- Lets’ design a simple circuit of an inverting amplifier which is to be discussed in this tutorial and the non-inverting amplifier with a few details provided is left for you as an exercise. Open the PSPICE design manager on your PC by typing design manager in the search bar. From the design manager click on the run schematic button to open a new blank schematic as shown in the figure below,
Figure 3: Opening Pspice
- After opening the new schematic before jumping into designing first save the schematic by clicking on the file button at the top left corner and then selecting save as so that we can access it anytime in the future. Refer to the figure below,
Figure 4: Saving schematic
- Click on the get new part icon at the top bar of the schematic window in order to search for the components that are needed for circuit designing.
Figure 5: Getting new part
- In the get new part window, type ‘Opamp’ it will display an amplifier available in PSPICE. From that list select a simple opamp as shown in the figure below,
Figure 6: Placing opamp
- Again open the get new part window and in the part name block type ‘R’, select the resistor from the list given and then click on place & close as shown in the figure below
Figure 7: Placing resistor
- Again open the get new part window and in the part name block type Vsin, select the supply from the list given and then click on place & close as shown in the figure below
Figure 8: Placing sin
- Next step is to place a ground, do the same again and in the part name type Gnd and select the ground and then click on place & close as shown in the figure below,
Figure 9: Placing ground
- The placed components in the schematic window are shown in the figure below,
Figure 10: Placed components
- Click on the draw wire icon at the top bar of the schematic window in order to connect the already placed components for circuit designing.
Figure 11: Drawing wire
- Connect all the components to complete the circuit diagram as shown in the figure below,
Figure 12: Complete circuit diagram
- On the top of the schematic window, click on the Voltage/Level Marker button as shown in the figure below,
Figure 13: Voltage marker
- Place it at the output resistor and at the input node as shown in the figure below,
Figure 14: Placed voltage marker
- Next step is to set the attributes of the input sinusoidal voltage supply. Double click on the input supply you connected in the circuit previously and set the magnitude of the voltage of the supply to 5V and the OFF voltage to 0 as shown in the figure below,
Figure 15: Sin attributes
- Next step is to adjust the properties of the simulations in order to produce the graph of the voltage at the marker. Click on analysis and then click on Setup as shown in the figure below
Figure 16: Analysis setup
- A widow will appear, click on the transient block on the window and adjust the properties of the window according to your requirement, refer to the figure below
Figure 17: Transient properties
- If we are interested in checking the voltage on a specific wire in spite of checking it at a node, double click on the wire and inn the window that appear as a result, type the name of the wire you want to label it with, as shown in the figure below,
Figure 18: Labeling the wires
- Now comes the simulation part, click on the analysis at the top bar of the schematic window and then click on simulate as shown in the figure below,
Figure 19: Simulating
- A schematic window will appear showing the voltage across the load resistor as shown in the figure below,
Figure 20: Output on an inverting amplifier
- The output of the circuit is in accordance with the output expected. An inverting amplifier as the name suggests inverts the voltage applied at the input side of the operational amplifier, and the magnitude of the output is amplified according to the gain of the amplifier adjusted with the resistors connected with it. As the input supply is connected to the inverting side of the amplifier i.e. the negative side of the amplifier hence the voltage at the output is 180 degrees out of phase of the input. The amplitude of the voltage can be increased or decreased according to the requirement using the gain formula provided in the introduction portion.
- Lets’ now move towards the non-inverting amplifier, the circuit diagram of a non-inverting amplifier, simulated in the schematic of PSPICE is shown in the figure below,
Figure 21: Non-inverting amplifier
- When this circuit is simulated according to the setup attributes discussed in the non-inverting circuit simulation the output as a result of the circuit simulation is shown in the figure below,
Figure 22: Non-Inverting amplifier
- As discussed in the introduction part, the output of the non-inverting amplifier is in phase with the input and its amplitude is increased or decreased according to the gain of the amplifier, the formula of which is given in the introduction portion. The simulation of the non-inverting amplifier is left for the reader as an exercise.
Exercise:
- Simulate the non-inverting amplifier circuit using the results and circuit diagram provided above.
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