can I use the AD8138 to add two differential signals?
Bandwidth is approx. 10 MHz.
Thanks in advance!
Differential amplifiers, like AD8138, can't be used to add two differential signals. They are called differential amps not only due to their input configuration but also by its output voltage which is the "difference" between the two different input voltage signals. Thus making these amplifiers a "subtractor".
If you're in need of a summing amplifier, you may use an operational amplifier like OP777 a micropower op amp or you may want to try AD830 a resistorless summing amplifier.
You may also want to read this mini tutorial MT-214 regarding inverting summing amplifier.
Hope this helps.