Duane,
I have experienced the same problem with the linear optocoupler design. We currently use this design for international products for voice applications, however the problem was detected at the compliance stage. We were powering the opto coupler and the op amps that drive the opto's off the -48 for safety compliance, which measured around 9 volts at the opto and op amp at 80mA loop current. Your distortion is probally being caused by low loop current. The major problem is that we found was to many voltage drop in the DAA, (ring detect, loop detect, and bridge) which decreases the voltage level down to 3 volts to drive the op amp and the opto. This gave us horrible THD levels along with other problems. We have now redesigned the DAA and have removed the Op Amp and Opto Coupler and returned to the transformer in design. I have heard through the grape vine that were not the only ones caught. I hope this has been helpful. Good Luck, Bill Pedersen GENTNER COMMUNICATIONS CORP. E-mail: [email protected]
