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DAC1405D750HW-C18

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DAC1405D750 6 © IDT 2012. All rights reserved.
Product data sheet Rev. 06 — 2 July 2012 31 of 41
Integrated Device Technology
DAC1405D750
Dual 14-bit DAC, up to 750 Msps; 4 and 8 interpolating
10.12 Analog output
The DAC1405D750 has two output channels each of which produces two complementary
current outputs. These allow the even-order harmonics and noise to be reduced. The pins
are IOUTAP/IOUTAN and IOUTBP/IOUTBN, respectively and need to be connected via a
load resistor R
L
to the 3.3 V analog power supply (V
DDA(3V3)
).
Refer to Figure 12 for the equivalent analog output circuit of one DAC. This circuit consists
of a parallel combination of NMOS current sources, and their associated switches, for
each segment.
The cascode source configuration increases the output impedance of the source, thus
improving the dynamic performance of the DAC by introducing less distortion.
The device can provide an output level of up to 2 V
o(p-p)
depending on the application, the
following stages and the targeted performances.
Table 41. Digital offset adjustment
Default settings are shown highlighted.
DAC_OFFSET[11:0] Offset applied
Decimal Two’s complement
2048 1000 0000 0000 4096
2047 1000 0000 0001 4094
... ... ...
1 1111 1111 1111 2
0 0000 0000 0000 0
+1 0000 0000 0001 +2
... ... ...
+2046 0111 1111 1110 +4092
+2047 0111 1111 1111 +4094
Fig 12. Equivalent analog output circuit (one DAC)
001aah019
V
DDA(3V3)
AGND
IOUTAP/IOUTBP
IOUTAN/IOUTBN
R
L
R
L
AGND
DAC1405D750 6 © IDT 2012. All rights reserved.
Product data sheet Rev. 06 — 2 July 2012 32 of 41
Integrated Device Technology
DAC1405D750
Dual 14-bit DAC, up to 750 Msps; 4 and 8 interpolating
10.13 Auxiliary DACs
The DAC1405D750 integrates 2 auxiliary DACs that can be used to compensate for any
offset between the DAC and the next stage in the transmission path.
Both auxiliary DACs have a resolution of 10-bit and are current sources (referenced to
ground).
(6)
The output current depends on the auxiliary DAC data:
(7)
(8)
Table 42 shows the output current as a function of the auxiliary DAC data.
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). In addition, it helps to match the impedance and provides
electrical isolation.
Table 42. Auxiliary DAC transfer function
Default settings are shown highlighted.
Data AUX[9:0] (binary) I
AUXP
(mA) I
AUXN
(mA)
0 00 0000 0000 0 2.2
... ... ... ...
512 10 0000 0000 1.1 1.1
... ... ... ...
1023 11 1111 1111 2.2 0
I
OAUX
I
AUXP
I
AUXN
+=
AUXP I
OAUX
AUX 9:0
1023
-------------------------


=
AUXN I
OAUX
(1023 A– UX 9:0
1023
---------------------------------------------


=
Fig 13. 1 V
o(p-p)
differential output with transformer
001aaj817
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)
DAC1405D750 6 © IDT 2012. All rights reserved.
Product data sheet Rev. 06 — 2 July 2012 33 of 41
Integrated Device Technology
DAC1405D750
Dual 14-bit DAC, up to 750 Msps; 4 and 8 interpolating
The DAC1405D750 differential outputs can operate up to 2 V
o(p-p)
. 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).
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
DAC1405D750 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.
Figure 15 provides an example of a connection to an AQM with a 1.7 V
I(cm)
common-mode input level.
Fig 14. 2 V
o(p-p)
differential output with transformer
001aaj818
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)
Fig 15. An example of a DC interface to a 1.7 V
I(cm)
AQM
001aaj541
51.1 Ω
51.1 Ω
442 Ω
442 Ω
V
DDA(3V3)
IOUTnP
IOUTnN
0 mA to 20 mA
BBP
(1)
IOUTnP/IOUTnN; V
o(cm)
= 2.67 V; V
o(dif)(p-p)
= 1.98 V
(2)
BBP/BBN; V
i(cm)
= 1.7 V; V
i(dif)(p-p)
= 1.26 V
BBN
AQM (V
i(cm)
= 1.7 V)
768 Ω 768 Ω
(1) (2)
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DAC1405D750HW-C18

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IC DAC 14BIT A-OUT 100HTQFP
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