While searching ADI's website for application information on their AD9747, I ran across applicaiton note AN-912 titled "Driving a Center-Tapped Transformer with a Balanced Current-Output DAC". This app note was tied to the AD9747, but the AD9747 is a differential output. My experience with differential signals is that the currents on the two outputs are equal and opposite, whereas the discussion of the balanced output indicated that the currents are not equal or opposite, but always sum to a constant output, e.g., I1 = x*Imax, and I2 = (1-x)*Imax.

Can anyone clear up the output behavior of the AD9747 (differential or balance), and point me to literature that explains the difference (if there is any difference) between the two modes?

Thank you

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Hi Roy -

Here is how the AD9747 current outputs work.

The current output appearing at IOUTP and IOUTN is a function of both the input code and IFS and can be expressed as:

IOUTP= (DAC DATA/2^{N}) ×IFS(1)IOUTN= ((2^{N}− 1) −DAC DATA)/ 2^{N}×IFS(2)where

DAC DATA= 0 to 2^{N}− 1, N is the number of bitsThanks,

Larry