The attached DTMF decoder configuration was taken from the datasheet of the MT8870 DTMF decoder but i'm seeing that in order to calculate the gain, the gain formula have a S...What is this S?... Do i just use the gain as Rf on R? The equation is on page 9 of the attached document.
The S thing lost me too The circuit you shown is differential, so the formula is not straight forward. Compare your pdf to the Mitel data sheet for the differential formula.
Lol...Oh well i'm seeing the voltage gain on page 5 for the differential configuration on the MItel datasheet is R5 on R which is the same as Rf on R in the testing circuit i attached earlier so that should be good...Thus it should be 150K/(56K+56K) which is approximately 1 so i don't see the sense using the differential configuration with a gain of almost 1 when there is a single ended input configuration with unity gain available. Unless the DTMF decoder is that sensitive to changes