Hello I have a question regarding generation of an ASK signal. I saw this simple circuit which generates a ASK signal using a NAND gate and I don't understand how it works. It consists of 2 circuits, one which generates the data signal frequency and the other which generates the carrier frequency, then they are both fed into a 2 input NAND which produces an output ASK signal (specifically OOK). How does this NAND work to generate ASK? I don't understand this at all. Thoughts?? Thanks for your help.

 

Here is a nice article - http://www.cs.ucl.ac.uk/staff/s.bhatti/D51-notes/node12.html - on ASK. The output of the carrier and the modulation can be easily done with an AND gate. Just imagine the carrier is a logic level pulse train instead of an AC signal/

 

Ohhh I see. So the the logic gate is used to modulate the data signal f(t) and carrier frequency sin(x). So to acheive the ASK modulated carrier signal ASK = f(t)sin(x), an AND gate will be used to perform the multiplication of carrier and data signal, right? Is there any reason why this particular circuit uses NAND gate? I am a little confused on this.

 

It only works for the ON/OFF variety of modulation. The carrier is present only when the data is HIGH. Same principle as Morse signaling.

 

The AND gate makes sense to me, if the modulating wave (digital signal) is high, and the carrier signal is high, then the and gate would produce a high signal, else a low. Using a NAND gate would be the opposite, so the modulated result wouldn't have teh same shape as the modulating wave. Am I seeing this wrong?