i am trying to transmit DTMF (with standard +/- 2.5KHz deviation) tones on various frequencies for one of my application using AD9910.
At present , i am trying to sample a DTMF tone and change the frequency in accordance with the tone's amplitude using a microcontroller. the sampling is higher than 8K, which seems to be sufficient as per general info available online. i have not been successful till now using this method. Somehow the tone frequencies are not same after demodulating.
i had a thought of giving the tone voltage directly onto the pll loop filter capacitor and see if the output gets modulated accordingly without PLL getting unlocked.(using 40 MHz crystal to get 1 GHz).
is there a way to frequency modulate the output frequencies just by adding an external voltage signal somewhere at the loop filter connections, but to keep the center frequencies around a predefined frequency based on the register configuration?