I'm going to use the AD1939 in a design where the differential to single ended output stage
is supplied by an assymetrical 0-8V power supply.
I would like to couple the DAC outputs in DC to the diff-to-SE stage, for which I
have an half-supply common mode voltage at 4V.
I start with the same schematic as the one presented in your evaluation kit for
- I replace the OP275 by a low noise opamp that works with my supply and input
- I change the connection to ground of one resistor by a connection to a
low impedance 4V common mode. (see attached figure).
When I simulate this with my spice, where the DAC is replaced by two
symmetrical voltage sources having a DC common mode at 1.5V, I get
the functionality I am looking for. But...
... doing this, I ask the DAC outputs to absorb about 400uA DC ( (4V - 1.5V) / 2*3k).
Is this going to work ? Is this going to degrade performance ?
To further understand, can we consider the DAC outputs like OPAMP outputs ?
If yes how much current can we sink/source on these ?
Thank you for your support,