Hi Treg'rs, I'm experiencing distortion problems with rail to rail opamps in a DAA design with a 3.3 volt supply. Opamps are spec'd to operate with +2.7V supply. I have used a similiar design with 2400 and 9600 (V22bis & V32) without problems. But, the 28.8 and 33.6 carriers are generating distortion when they pass through the opamps. Opamps are biased differential, meaning there is a receive + and - opamps carrying half the signal. i.e. they are referenced to a +1.65 V pseudo ground. The supply is provided by batteries so supply impedance is not the problem.
This design is required to support cellular and Audio-span restricting the use of a passive hybrid. Mike and headset are required. Has anyone had success using discrete rail to rail opamps at 3.3V in a differential configuration for V.34.? I have done this with a single 5 volt supply. My client has resisted using a small switching pump to get 5 volts for opamps. Which does not have the problem. Does anyone have any ideas they would be willing to pass on? I'm not looking for a design I just need to be pointed in the right direction. Thank you in advance. Regards, Duane
