SLAS536D September 2007 – November 2021 DAC5662A
PRODUCTION DATA
Using an RF transformer provides a convenient way of converting the differential output signal into a single-ended signal while achieving excellent dynamic performance. The appropriate transformer should be carefully selected based on the output frequency spectrum and impedance requirements.
The differential transformer configuration has the benefit of significantly reducing common-mode signals, thus improving the dynamic performance over a wide range of frequencies. Furthermore, by selecting a suitable impedance ratio (winding ratio) the transformer can be used to provide optimum impedance matching while controlling the compliance voltage for the converter outputs.
Figure 8-2 and Figure 8-3 show 50-Ω doubly terminated transformer configurations with 1:1 and 4:1 impedance ratios, respectively. Note that the center tap of the primary input of the transformer has to be grounded to enable a dc-current flow. Applying a 20-mA full-scale output current would lead to a 0.5-VPP output for a 1:1 transformer and a 1-VPP output for a 4:1 transformer. In general, the 1:1 transformer configuration has a better output distortion, but the 4:1 transformer has 6 dB higher output power.