JAJSTV7 March 2024 DAC39RF10-SEP , DAC39RF10-SP , DAC39RFS10-SEP , DAC39RFS10-SP
PRODMIX
The device contains two optional features to improve non-linearity due to current segment and switch timing mismatch: Dynamic element Mixing (DEM) and dither.
The DAC core consists of
DEM randomizes which MSB and ULSB current sources/switches are used to generate the output, which whitens the non-linearity due to mismatches between the current sources and switch timing. The DEM_DACA/B and DEM_ADJ registers control the frequency and amplitude of the shift in current sources/segments.
Dither add or subtracts 8 different digital code values to the digital data which are then canceled by switching additional current sources with the same amplitude. The digital data path is expanded so the full 16-bit range is maintained. The DITH_DACA/B registers control the frequency of the dither.
Using DEM generally improves low order harmonics near fullscale. Dither generally improves higher order harmonics near fullscale and all harmonics at lower digital amplitudes. Both DEM and dither increase the noise floor (both amplitude and phase) of the output due to the whitening of the non-linearity and the additional switching activity. This is reduced by DEM and dither settings with lower switching activity, that is. data dependent or reduced activity DEM. However, data dependent or reduced activity DEM is less effective at higher output frequencies. For data sheet specification testing in Electrical Characteristics - AC Specifications, data dependent DEM (DEM_ADJ = 1) is used below 750MHz and normal activity DEM (DEM_ADJ = 0) above 750MHz, but different settings (including disabling DEM and/or dither) can be tested and the best chosen based on the specific use case.