DAC5672 Datasheet, PDF (18/23 Pages) Texas Instruments – DUAL, 14-BIT 200 MSPS DIGITAL - TO - ANALOG CONVERTER

DAC5672
SLAS440 – NOVEMBER 2004
www.ti.com
The single-ended configuration may be considered for applications requiring a unipolar output voltage.
Connecting a resistor from either one of the outputs to ground converts the output current into a
ground-referenced voltage signal. To improve on the dc linearity by maintaining a virtual ground, an I-to-V or
op-amp configuration may be considered.
Differential With Transformer
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 must 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 provide optimum impedance matching while controlling the
compliance voltage for the converter outputs.
Figure 22 and Figure 23 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-V_PP output for a 1:1 transformer
and a 1-V_PP output for a 4:1 transformer. In general, the 1:1 transformer configuration will have slightly better
output distortion, but the 4:1 transformer will have 6 dB higher output power.
50 Ω
IOUT1
1:1
100 Ω
AGND
IOUT2
50 Ω
R_LOAD
50 Ω
Figure 22. Driving a Doubly-Terminated 50-Ω Cable Using a 1:1 Impedance Ratio Transformer
IOUT1
IOUT2
100 Ω
4:1
AGND
100 Ω
R_LOAD
50 Ω
Figure 23. Driving a Doubly-Terminated 50-Ω Cable Using a 4:1 Impedance Ratio Transformer
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