Help me study for my Engineering class. I’m stuck and don’t understand.


Write a detailed procedure to design the circuits in questions 2-4 in LTSpice and using a breadboard to build the circuit. Make sure you take a lot of screen shots of the LTSpice model and output and briefly explain in your own words the steps needed to get the correct simulation. Include pictures of the actual circuit you built and the inputs and outputs of the signal generator (input) and oscilloscope (output). Make sure there is a title page and all figures are easily visible. There should be two parts, one for the LTSpice model and the other for the circuit design, there should be a procedure for both. Be sure to answer question 5 in your own words.

1. LTSpice Introduction

LTSpice is a graphical SPICE program, which allows you to simulate a large variety of circuits on your computer. You can download LTSpice for free on your personal computer:
Online tutorial:
Include a screenshot of the startup screen after download.2. Simulate Diode Rectifier

Here we will build a simple rectifier circuit in LTSpice and record how it behaves. First we need to add the resistors and diodes, and wire them together and to ground. From Left to right on the LTSpice toolbar:

Add component and wires. Click to select a component or wire and click again to place. Your circuit should now look like the following:

We now want to set the resistor values. Right click on the resistor and set the resistance to 1k



Now right click on the diodes, click ‘Pick New Diode’ and select the 1N4148. Note various different diode models canbe selected. We are choosing a basic silicon diode

Add a voltage source (sinusoidal input). Click on add component on your toolbar:


Place the voltage source, wire it, and your circuit should now look like the following:


Right click on the voltage source and set it to a 60 Hz sine wave with 2.5 V amplitude.

Add net names. This labels voltage nodes for later reference.

Now let’s simulate the circuit using a transient analysis. Click the simulate button on the toolbar and select theTransient menu. Set the stop time to 0.1s, start time at 0s, and timestep to 0.001s.



Click with the voltage probe on the wires where we want to measure the voltage and you should see the following output. Plot the input voltage with the left and right output voltage. Identify which side behave like an inverting rectifier.

3. DC Bias of npn BJT

Here we will examine the BJT current with the following bias circuit. Select and place a two voltage sources, your grounds, and an npn transistor. Select the 2N3904 transistor just as you selected a specific diode in the previous example. Set the appropriate net names.

We will now do a DC sweep of the circuit. Click the simulate button, and select the DC sweep menu. Enter the appropriate values for the 1st source and 2nd source and shown below.


Now click on the wire of the BJT with the current probe. You should see the cursor change as you hover over the BJT component.

You should see a nice set of curves with the ICE current plotted against VCE with each curve having a different VBE value. These curves will become very familiar when you begin to study the DC characteristics of the BJT. Plot the IV Curves for a various combinations of V1 and V2, be sure to include the reverse bias part of the IV curve.


4. Basic BJT amplifier

We will now simulate a very simple common-emitter amplifier by slightly altering the previous circuit. Using your knowledge from the previous examples, put together this circuit, with the appropriate 2N3904 npn transistor, 5k resistor, 8V voltage source at the top, and a 0.65V DC input voltage with a 10 mV 10kHz sine wave on top. Perform a transient analysis lasting about 1ms with 1μs time steps.


Plot Vout and Vin waveforms. The output waveform should be an amplified version of the input wave.

Then, build the circuit using actual discrete components (i.e. resistors, BJT’s) on a breadboard, and seethe output waveform. Does it match with the simulation result? Take images of circuit and include in your report.

5. Simulation vs Real Circuit Comparison

Analyze the inputs and outputs of the real circuit and LTSpice model. How do they differ? Try a higher frequency input for the LTSpice Model and circuit, how do the results from both differ. Is the LTSpice model a good representation of the real-life circuit?

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