SBOS778D April 2016 – April 2021 THS4551
One of the most useful features supported by the FDA device is an easy conversion from a single-ended input to a differential output centered on a user-controlled, common-mode level. Although the output side is relatively straightforward, the device input pins move in a common-mode manner with the input signal. The common-mode voltage at the input pins, which moves with the input signal, increases the apparent input impedance to be greater than the RG value. The input active impedance issue applies to both ac- and dc-coupled designs, and requires somewhat more complex solutions for the resistors to account for this active impedance, as discussed in the Section 9.3.2.