# Lab 4:Diodes solution

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Objectives
• Gain practical experience with the behavior of silicon diodes under forward and reverse bias.
• Explore the use of diode devices in rectifying, limiting, and DC restoration circuits.
Parts and Equipment Required
Components and Materials Needed:
• 10kΩ resistor (1).
• 10nF capacitor (1).
• 1N914 diodes (4).
Equipment to be Used:
• Banana cable sets (5).
• Oscilloscope probes (2).
• BNC-to-BNC cable (1).
• BNC-to-alligator cable (1).
1 Pre-Lab Exercises
In this lab we will perform experiments on six circuits, which are shown below. In each circuit, assume that R is 10k
ohms, and C is 10nF. The 1N914 diode has n=2 and a forward voltage drop of 655mV at a forward current of 1mA.
Utah State University Spring 2015 1
ECE 3410– Microelectronics I Lab 4: Diodes
Exercise 1. For both of the circuits shown in Fig. 1, identify the logical function (if V1 and V2 represent binary
signals). Determine the value of vout when V1 = 3V and V2 = 2V. Determine the value of vout when
V2 = 2.8V, 3.2V and 4V.
V1
D1
V2
D2
vout
R
vout
D2
V2
D1
V1
R
5V
Figure 1: Diode logic circuits.
Exercise 2. Figure 2 shows the schematic diagram for a half-wave rectifier circuit. If vin is a 1kHz sinusoid with zero
offset and a zero-to-peak amplitude of 2V, predict the waveform of vout as accurately as possible without
using iterative analysis or SPICE simulations. Sketch the predicted waveform in your lab book.
vin
D
R
vout
Figure 2: Half-wave rectifier circuit.
Exercise 3. Fig. 3 shows the schematic diagram for a half-wave peak rectifier circuit. Again assume that vin is a
sinusoid with zero offset and zero-to-peak amplitude of 2V. Predict the output waveforms when vin has
a frequency of 1kHz, 10 kHz, and 100kHz. Sketch the predicted waveforms in your lab book.
Exercise 4. Fig. 4 shows the schematic diagram for a voltage-limiting circuit. Assume that vin is a 1kHz sinusoid
with zero offset and zero-to-peak amplitude of 3V. Using the constant voltage- drop model, predict the
output waveform as accurately as possible, and sketch the prediction in your lab book.
Utah State University Spring 2015 2
ECE 3410– Microelectronics I Lab 4: Diodes
vin
D
C
vout
R
Figure 3: Peak rectifier circuit.
vin
R
vout
D1
D2 D3
D4
Figure 4: Voltage limiter circuit.
Exercise 5. Fig. 5 shows the schematic diagram for a DC restoration circuit (a.k.a. a clamped capacitor circuit).
Assume that vin is a 1kHz sinusoid with a 1V offset and a zero-to-peak amplitude of 3V. Using the
constant voltage drop model, predict the output waveform as accurately as possible. Also predict the
offset of the output waveform. Sketch the predicted waveform in your lab book.
vin
C
D
vout
Figure 5: DC restoration circuit.
2 Physical Experiments
Procedure 1. Repeat the following procedures for both of the diode gates described in Fig. 1.
Step A. Holding V1 fixed at 3V, adjust V2 from 2V to 4V in steps of 0.5V.
Step B. Plot the results in your lab book. How do the measured results compare with your predictions?
Utah State University Spring 2015 3
ECE 3410– Microelectronics I Lab 4: Diodes
Procedure 2. Set up the half-wave rectifier circuit. Use the function generator to supply vin as specified in the prelab.
Step A. Measure and record the output waveform, and sketch the result in your lab book. Be sure to
accurately measure the duration of forward bias, the peak output voltage, and the output voltage
under reverse bias.
Step B. How do the measured results differ from your predictions?
Procedure 3. Set up the half-wave peak rectifier circuit. Use the function generator to supply vin as specified in the
prelab.
Step A. Carefully measure and record the output waveforms for vin at 1kHz, 10kHz and 100kHz.
Step B. Measure and record the peak-to-peak amplitude of the ripple in the output waveform at 1kHz,
10kHz and 100kHz.
Procedure 4. Set up the limiter circuit as specified in the prelab.
Step A. Measure and record the output waveform when vin has a peak-to-peak voltage of 1 V.
Step B. Repeat the above measurement when vin has a peak-to-peak voltage of 4 V.
Step C. How do the results compare to your expectations? Did you accurately predict the clipping voltage?
If not, suggest reasons for the discrepancy.
Procedure 5. Set up the DC restoration circuit as specified in the prelab.
Step A. Measure and record the output waveform. Make sure you have DC Coupling in Channel 1
and Channel 2 settings. Ideally, the output offset should equal half its amplitude (i.e. the low
peak of the sinusoid should be at ground).
Step B. Measure the actual minimum value of the output waveform. This value is expected to be slightly
lower than the minimum value of the input waveform. Explain the measured result.
Utah State University Spring 2015 4
ECE 3410– Microelectronics I Lab 4: Diodes
3 Post-Lab
In your lab book, write a summary of your findings, and write a brief report describing your objectives, methods and
major findings. Submit this report to the TA or Instructor along with your Lab Book.