Name ____________________________
ELEC 416 Communication Engineering
Computer Design Project II
Due on Tuesday 14 October 2014
AM Modulation and Demodulation
Objectives: 1) Simulate a DSBLC modulator and envelope detector.
2) Investigate the spectral characteristics of the DSBLC signal.
Assignment:
SWITCHING MODULATOR
1) Use PSpice software to simulate the switching modulator of Figure 3.5a of your text. Use two VSIN
sources to produce a DSBLC signal given by
s(𝑡) = 2[1 + 0.8 cos(2𝜋(103 )𝑡)] cos(2𝜋(104 )𝑡)
2) Referring to Figure 3.5 display a trace of 𝑣1 (𝑡) by running a Time Domain Transient analysis
showing 2 ms of data. Also, display a trace of the FFT of 𝑣1 (𝑡) using the FFT button in the output
window.
3) Repeat step 2 for 𝑣2 (𝑡).
4) Design a parallel RLC BPF similar to the one below to extract the desired DSBLC waveform.
D1N4002
R1
V
D1
500
2
V2
VOFF = 1
VAMPL = 0.8
FREQ = 1k
m(t)
R2
L1
C1
1k
1
V1
VOFF = 0
VAMPL = 2
FREQ = 10k
c(t)
0
5) Display a trace of the signal at the output of the BPF showing 10 ms of data, and also the
corresponding FFT on separate plots.
ENVELOPE DETECTOR
6) Design an envelope detector (similar to that in Figure 3.7 of text) to extract the signal m(t) from the
output of the BPF.
7) Display a trace of the signal at the output of the envelope detector showing 10 ms of data, and the
corresponding FFT on separate plots.
Report: Please organize your work as indicated below.
1. Cover sheet
- Original Project assignment sheet with your name added.
2. Section 1
- Step 1 Pspice circuit with your chosen design values.
- Time domain and frequency domain plots for 𝑣1 (𝑡).
3. Section 2
- Time domain and frequency domain plots for 𝑣2 (𝑡).
a. What is the percent modulation?
b. Discuss and compare the frequency content of 𝑣1 (𝑡)𝑎𝑛𝑑 𝑣2 (𝑡).
4. Section 3
- Step 4 Pspice BPF circuit showing your chosen design values.
- Step 5 Time domain and frequency domain plots.
- Discuss the effectiveness of your BPF.
5. Section 4
- Step 6 Pspice circuit showing your envelope detector design values.
- Step 7 Time and frequency domain outputs of the envelope detector.
- Discuss the effectiveness of your envelope detector.