What determines the AD6676’s full-scale input setting?

Document created by Anthony.DeSimone Employee on Nov 17, 2014Last modified by Anthony.DeSimone Employee on Nov 17, 2014
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To a first order, the full-scale setting (PIN_0dBFS) is given by the following equation with IDACIFS being the full-scale current setting of the 1st stage feedback DAC and  RIN being the IF input resistance.


PIN_0dBFS = 10 × log10(1/2 × RIN × IDAC1FS2)


IDACIFS can be varied over a 4 to 1 mA range thus allowing PIN_0dBFS to be varied over a 12 dB range. At the max setting of 4 mA and an RIN of 60 ohms, the theoretical PIN_0dBFS is -3.2 dBm.  In practice, the IF, FADC, and Lext settings have a secondary affect that may result in the PIN_0dBFS being up to 1 dB higher than the theoretical value.