PAM schematic or wiring diagram for Digital Communications

makovx

Hi. Who among you know a site where I can find a wiring diagram or schematic diagram of PAM (Pulse Amplitude Modulation)? I badly needed a diagram of it for my prototype in Digital Communications.

I've been searching for it in Google but it only gave me different diagrams and I can't tell which is which because I've never seen any PAM schematic diagram before. :(

The professor only told us that our second prototype is PAM. He only gave a brief description about what a PAM does. If I have not searched in the internet, I won't know that the meaning of PAM is Pulse Amplitude Modulation.

An article about what a PAM is, can be found in http://www.tech-faq.com/pulse-amplitude-modulation.html

I hope you can help me. Thanks!

berkeman

So to put out pulses of various amplitudes, you can use a Digital-to-Analog Converter (DAC). Probably the simplest version for you to use in your project would be an R-2R Ladder DAC. Alternately, you could use a current output mode DAC, and feed the output current into a current-to-voltage converter circuit (like with an opamp).

So that should give you some good search terms to use in your next try at Google and Wikipedia.org -- also try some of the DAC manufacturer websites like Maxim and Linear Technology, to look for application notes and tutorials.

Let us know what you find!

dlgoff

I was looking around earlier and got lots of hits from Google Scholar from "pulse height modulation".
http://scholar.google.com/scholar?q=...+modulation%22

makovx

Thank you for your immediate response :)

I found a pdf file about a laboratory excercise in PAM (and demodulation).
I think it's the one Im looking for.


The title is:
LAB - 3
PULSE AMPLITUDE MODULATION & DEMODULATION

and the circuit diagram is:


My problem this time is the hardware requirements.
I don't know what is the meaning of AFO, CRO and CPS.
Can you pls tell me what are these things? So that I can go to a hardware shop immediately :)

Thanks!

berkeman

From what I saw in the PAM links, the output is a series of rectangular pulses, with different amplitude rectangular pulses representing the encoded (modulated) information.

The schematic you posted looks to be an ON-OFF modulation of a sinusoidal source. From the title of the schematic/lab, it appears to be a different interpretation of PAM. Do you think that is what your lab is about?

makovx

Yes, that's the PAM I exactly need.
You mean the circuit diagram I posted is a different interpretation of PAM. I see.

I'll try using the DAC you suggested then.
Thanks :)