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Differential With Transformer

IOUT1

1:1

IOUT2

50

Ω

50

Ω

50

Ω

100

Ω

AGND

IOUT1

4:1

IOUT2

100

Ω

100

Ω

50

Ω

AGND

DAC5652

SLAS452A – MARCH 2005 – REVISED FEBRUARY 2006

APPLICATION INFORMATION (continued)

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 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 18 and Figure 19 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

output distortion, but the 4:1 transformer will have 6 dB higher output power.

Figure 18. Driving a Doubly-Terminated 50-

Ω Cable Using a 1:1 Impedance Ratio Transformer

Figure 19. Driving a Doubly-Terminated 50-

Ω Cable Using a 4:1 Impedance Ratio Transformer

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