I have implemented the MT8870 Decoder like the application note design. The circuit works will if using a local telephone, but if I tried to decoded the tones from the telephone exchange the circuit most off the time will be not able to detect the tone.... is this related to the 600ohm impedance or related to R and C values ???!!!!
I'll be thankful if anyone have some ideas ....
I'll be thankful if anyone have some ideas ....