Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Generalized LPF for DAC
I am putting together a design for a DAC project, nothing revolutionary, but I was hoping to get some general opinions on the design of the LPF.
The DAC I am planning on using has differential current output, so the first stage will be I-V conversion for each output. After this comes my problem: I would like to have differential outputs, so I am tempted to do a 2-pole Butterworth filter (i.e. Crystal AN55, 50Hkz corner frequency) seperately on the positive and negative outputs, and use these as the differential outputs. I would then use a differential-to-single-ended converter at the amp side, reaping the benefits of balanced lines without any distortion overhead from the converter.
However, I am concerned that due to my inability to closely match resistor and capacitor values in the filter I will introduce differences between the positive and negative outputs that will reduce CMR or even degrade the actual signal.
How would you implement this? Thanks very much for any insights.