Datasheet

Differential With Transformer
IOUT1
1:1
IOUT2
50 Ω
50 Ω
R
LOAD
50 Ω
100 Ω
AGND
IOUT1
4:1
IOUT2
100 Ω
100 Ω
R
LOAD
50 Ω
AGND
DAC5662
www.ti.com ................................................................................................................................................................ SLAS425B – JULY 2004 – REVISED MAY 2007
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.
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 21 and Figure 22 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.
Figure 21. Driving a Doubly Terminated 50- Ω Cable Using a 1:1 Impedance Ratio Transformer
Figure 22. Driving a Doubly Terminated 50- Ω Cable Using a 4:1 Impedance Ratio Transformer
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