Design Project: ASK-FSK Waveform Generation

Introduction

Two types of digital-to-analog modulation techniques are Amplitude Shift Keying (ASK) and Frequency Shift Keying (FSK). In ASK, two different amplitudes, and only two, represent the digital information. In FSK, only two different frequencies are used to represent the digital data.

The Goal

The goal of the design project is to design a Commsim circuit that will generate the following analog carrier based on a digital input stream:

Figure 1: ASK-FSK modulated carrier. The digital input stream is 00 10 01 11 01 00 11 10 00 10. Each pair of bits represents one bit each from two digital input signals .

What to Submit

You must submit the following:

1. A paper describing your design process, how you made decisions, trouble you had, changes you made to the design to make it work, how you figured out significant values (frequencies,etc).

2. A working Commsim circuit file that generates the waveform in Figure 1 when simulated.

Hint

When you look at the waveform that is generated by the digital to analog importer circuit for the project, when you look at that waveform in the figure 1, on the project page, what you want to do first is look at the waveform that is generated for a particular bit pattern. And you know the bit pattern is 00, you get the same type of waveform, whenever it's 11, you get the same type of waveform. So once you do that, then I think you'll feel that there is some other relationship between those two bits, the two A and B input bits. There's a relation between those and what type of waveform you get. So that's one thing.

Something else you would think about is that you need, well one way to do this is to use some kind of analog multiplexer. Now, that would easily be done with a switch, wouldn't it? A little four position rotary switch and you could very simply put, you know, the four different kinds of waveforms that you have there, and each of the input of the rotary switch, and assign position of the rotary switch to those unique two bit patterns [indecipherable]. And you know just rapidly switch that thing from pole to pole, to get a little waveform from that, that's exactly what your electronic circuit will do, you have to go and find the electronic equivalent of that analog switch, they make analog multiplexers, they do for analog signals what digital multiplexers do for digital signals.

So you find analog the mux and then you figure out how to program the inputs to the right waveforms to get the signal out. What else, how did I come out with that waveform? Well, that's very interesting! This is probably the key to finding out what's going on here. I was investigating, I started looking through the example circuits that came with [indecipherable] and I would open up an example circuit and I would simulate it and I would see what I got on the display and at one point I was, ooh! That's what I need for the project, and that's about a big hint as I can get here.

Research Project

There are two main purposes of the Research / Design Project:

1. To investigate the operation of additional communication technologies.

2. To develop a working communication system.

In the research portion, the student will read three additional chapters from the textbook.

One of the three must be Chapter 10: Wireless Digital Communications.

The other two chapters must be chosen from the following:

• Chapter 4: Single-sideband Communications

• Chapter 7: Communication Techniques

• Chapter 14: Antennas

• Chapter 15: Waveguides and Radar

• Chapter 16: Microwaves and Lasers

A short paper (3-5 pages) covering the new topics and their applications must be submitted.

In the design portion, the student will design a communication transmitter circuit supplied by the instructor. The Commsim software will be used during the design. This project is not based on any of the five chapters 4, 7, 14, 15, or 16 but on material covered by all students during the regular coursework. Note however that creativity and investigation will be necessary.
Each student will be responsible for handing in the following:

1. A 3-5 page paper describing the information learned during the research, with specific references to examples within the chosen chapters.

2. A detailed description of the communication system designed by the student, including all relevant theory, diagrams, schematics, state diagrams, graphs, and working Commsim simulation files.