DAC1405D650 5 © IDT 2012. All rights reserved.
Product data sheet Rev. 05 — 2 July 2012 32 of 41
Integrated Device Technology
DAC1405D650
Dual 14-bit DAC, up to 650 Msps; 2, 4 and 8 interpolating
10.14 Output configuration
10.14.1 Basic output configuration
The use of a differentially-coupled transformer output provides optimum distortion
performance (see Figure 13 “1 V
o(p-p)
differential output with transformer”). In addition, it
helps to match the impedance and provides electrical isolation.
The DAC1405D650 can operate up to 2 V
o(p-p)
differential outputs. In this configuration, it
is recommended to connect the center tap of the transformer to a 62 resistor connected
to the 3.3 V analog power supply, in order to adjust the DC common mode to
approximately 2.7 V (see Figure 14 “2 V
o(p-p)
differential output with transformer”).
10.14.2 DC interface to an Analog Quadrature Modulator (AQM)
When the system operation requires to keep the DC component of the spectrum, the
DAC1405D650 can use a DC interface to connect to an AQM. In this case, the offset
compensation for LO cancellation can be made with the use of the digital offset control in
the DAC.
Fig 13. 1 V
o(p-p)
differential output with transformer
Fig 14. 2 V
o(p-p)
differential output with transformer
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50 Ω
50 Ω
50 Ω
IOUTnP/IOUTnN; V
o(cm)
= 2.8 V; V
o(dif)(p-p)
= 1 V
IOUTnP
IOUTnN
0 mA to 20 mA
2:1
0 mA to 20 mA
V
DDA(3V3)
V
DDA(3V3)
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50 Ω
100 Ω
100 Ω
IOUTnP/IOUTnN; V
o(cm)
= 2.7 V; V
o(dif)(p-p)
= 2 V
IOUTnP
IOUTnN
0 mA to 20 mA
4:1
0 mA to 20 mA
V
DDA(3V3)
62 Ω
V
DDA(3V3)
V
DDA(3V3)
