Diodes and transistors are the fundamental building block of digital electronics. A diode is made of a simple p-n junction that allows electrons to flow in one direction but not in the other. A transistor is a semiconductor device that acts as a controllable valve for electrons, the same way as a valve or faucet does for water. A field effect transistor (FET) for example, conducts electrons only when exposed to a small electric field, thus are widely used as a switch in computer logic circuits. The concepts such as Boolean algebra, microcontrollers, processor I/O, and digital systems interfacing are all based on diodes and transistors.
In analog circuits, diodes and transistors are heavily involved in signal conditioning and any other processes required to make the sensor output suitable for further processing.
Pre-lab Assignment (10 pts in total):
• Run “Pre-lab assignment – Clipper” and observe the unidirectional behavior of the diodes. i.e. positive and negative clipping, or the removal of top half or bottom half of an input signal. Put a screenshot picture of the results from both XSC1 and XSC2 in your lab report (2 pts).
• Research diode; (1) include a diagram (cite the source if it is not your own drawing) of a typical PN junction type diode in your lab report, with the depletion zone and current flow direction shown or marked on it (4 pts) and (2) provide a brief explain why the two plateau voltage values seen from the two XSC’s for the two clipper circuits in “Pre-lab assignment -Clipper” are +0.63 V and -0.63 V, respectively (4 pts). (Hint: the diodes used in Multisim simulations are Si-based, PN junction type and research the bias voltage of such type of diodes).
• This is one source where you can find information about diodes and signal clipping (https://www.electronics-tutorials.ws/diode/diode-clipping-circuits.html)
Exercise #1: Clipper Part I (25 pts in total)
- Open and run “Exercise #1 – Clipper Part I” and examine how each of these circuits works in clipping the signal: XSC1 and XSC2 are what you have seen in “Pre-lab assignment – Clipper”; XSC3 and XSC4 are when a power source is added but in two different directions; XSC5 show what happens when two diodes are involved; XSC6 display the input (which is the same for all the other circuits). With these simulations, we learn that a deaired output signal, shape of the waveform (or level of clipping) and clipping voltages (the plateau voltages), using a diode and or in combination of a power source.
- Assignment #1-0 (5 pts): Put a screenshot picture of XSC3, XSC4, XSC5, and XSC6 in your lab report.
- Assignment #1-1 (10 pts): Add two NI ELVISmx Oscilloscopes (available from Multisim “NI ELVISmx Instrument” toolbar) to the two clipping circuits XSC1 and XSC2 in “Exercise #1 – Clipper Part I” and connect them with the circuits the same way as XSC1 and XSC2. Replace the AC power sources of these two clipping circuits with two NI ELVISmx Function Generators (available from Multisim “NI ELVISmx Instrument” toolbar) and set both with Vpp = 10 V and Frequency = 1 kHz. Run these two clipping circuits again, one after another, and put a screenshot picture of these two NI ELVISmx Oscilloscopes, side by side with their counterparts’, XSC1’s and XSC2’s, in your lab report, respectively. Are the waveforms from each pair of oscilloscopes, i.e. XSCx/NI ELVISmx Oscilloscope, identical/similar to or different from each other (The cursors on NI ELVISmx Oscilloscope in Multism do not function the same way as the same virtual NI ELVISmx Oscilloscope does when used in conjunction with ELVIS (where they INDICATE voltage readings as you move them along the waveform). Use SAME scales, “Timebase” and “Channel A” XSC vs. “Time/Div” and “Scale Volts/Div” in NI ELVISmx Oscilloscope to help you answer this question)?
NOTES: The physical circuit on an ELVIS equivalent to XSC2 would look like the one that is shown in Figure 1-1.
- Assignment #1-2 (10 pts): Now do the same for the clipping circuit XSC3 in “Exercise #1 – Clipper Part I”, i.e. adding an NI ELVISmx Oscilloscope as well as replacing the AC power scource with an NI ELVISmx Function Generator. Besides, put down an NI ELVISmx Variable Power Supply (available from Multisim “NI ELVISmx Instrument” toolbar), set -2 V, and replace the -2 V DC power supply with it. Re-connect the circuit with these instruments and run this clipping circuit again; put a screenshot picture of XSC3 and NI ELVISmx Oscilloscope, side by side, in your lab report. Are the waveforms from both scopes identical?
NOTES: The physical circuit on an ELVIS equivalent to XSC3 would look like the on that is shown in Figure 1-2, with a -2 V DC power supply.
Exercise #2: Clipper Part II (40 pts in total)
- Open and run “Exercise #2 – Clipper Part II” and examine how a two-diode clipper circuit removes portions of an input signal for desired clipping voltages. Assignment #2-0 (5 pts): Put a screenshot picture of XSC3 and XSC5 in your lab report.
- Assignment #2-1 (15 pts): Based on what you have learned by completing Exercise #1 and Assignment #2-0 with respect to how diodes work in clipping a signal, using power sources and diodes, design a clipper circuit in Multisim with which you can obtain an output signal that looks identical to the one shown in Figure 2-1, i.e. clipping at both levels and the clipping voltages are 1.63 and -3.60 V, respectively. Put a screenshot picture of Multisim circuit design and the XSC result in your lab report.
- Assignment #2-2 (20 pts): Add an NI ELVISmx Function Generator and two NI ELVISmx Variable Power Supplies (all available from Multisim “NI ELVISmx Instrument” toolbar) to the clipping circuit XSC3 in “Exercise #2 – Clipper Part II” and replace their countparts, XSC3 and -2 and 2 V DC power supplies. Place an NI ELVISmx Oscilloscope and connect it to the circuit the same way as XSC3. Set the instruments properly (amplitude, frequenct, power supplies etc.). Run the simulation again; put a screenshot picture of XSC3 and NI ELVISmx Oscilloscope, side by side, in your lab report. Are the waveforms from both scopes identical?
Exercise #3: Transistor (25 pts in total) – IGNORE
- Open and run “Exercise #3 – CommonBase” and find the values needed to fill out Table 1.
NOTES: XMM1, XMM2, XMM3, and XMM4 are for measuring the DC components, i.e. IE and IC, VE, and VC, while XSC1 is for the AC.
- Assignment #3-1 (5 pts): Put a screenshot picture of your Multisim results (the XMM’s and XSC1) in your lab report.
- Assignment #3-2 (10 pts): Build the circuit on ELVIS II using Figure 3 (the black band at one end of the diode indicats the direction of current flow); examine the circuit with the built-in Oscilloscope through LabVIEW; put a screenshot picture of your Oscilloscope results in your lab report.
NOTES: The input amplitude used in “Exercise #3 – CommonBase” for Multisim simulations is 10 mVrms and equals to 28.28 mVpp, the value to be used as the input amplitude for the ELVIS II Function Generator.
- Assignment #3-3 (10 pts): Complete Table 1 with the numerical data obtained from both Multisim simulations and ELVIS II measurements, as well as calculations using the data.
Figure 1-1 Circuit for “Exercise #1 – Clipper Part I” (without power supply)
Figure 1-2 Circuit for “Exercise #1 – Clipper Part I” (with a -2 V power supply)
Figure 2-1 Expected output from completing Assignment #2-1
Figure 3 Circuit for Exercise #3: Transistor
Table 1 for Assignment #3-3 (Report your data with 3 significant figures)
Quantity Multisim Simulated ELVIS II Measured
IE (mA)
IC (mA)
VRC (V)
VRE (V)
Open-circuit voltage gain
(Av = VRC/VRE)
Short-circuit current gain
(Ai = IE/IC)
Voltage gain
(dB, from scope) *
Voltage gain
(dB, from Bode Plotter)
Sample Solution
