AD9778A-DPG2-EBZ Analog Devices Inc, AD9778A-DPG2-EBZ Datasheet - Page 39
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AD9778A-DPG2-EBZ
Manufacturer Part Number
AD9778A-DPG2-EBZ
Description
Dual 16B, 1.0 GSPS TxDAC
Manufacturer
Analog Devices Inc
Datasheet
1.AD9776ABSVZ.pdf
(60 pages)
Specifications of AD9778A-DPG2-EBZ
Number Of Dac's
2
Number Of Bits
14
Outputs And Type
2, Differential
Sampling Rate (per Second)
1G
Data Interface
Parallel
Dac Type
Current
Voltage Supply Source
Analog and Digital
Operating Temperature
-40°C ~ 85°C
Utilized Ic / Part
AD9778A
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
FULL-SCALE CURRENT GENERATION
INTERNAL REFERENCE
Full-scale current on the I DAC and Q DAC can be set from
8.66 mA to 31.66 mA. Initially, the 1.2 V band gap reference is
used to set up a current in an external resistor connected to I120
(Pin 75). A simplified block diagram of the reference circuitry is
shown in Figure 75. The recommended value for the external
resistor is 10 kΩ, which sets up an I
120 μA, which in turn provides a DAC output full-scale current
of 20 mA. Because the gain error is a linear function of this resistor,
a high precision resistor improves gain matching to the internal
matching specification of the devices. Internal current mirrors
provide a current-gain scaling, where I DAC or Q DAC gain is a
10-bit word in the SPI port register (Register 0x0B, Register 0x0C,
Register 0x0F, and Register 0x10). The default value for the DAC
gain registers gives an I
I
FS
=
1.2
R
V
×
⎛
⎜
⎝
27
12
+
FS
⎛
⎜
⎝
of approximately 20 mA. I
1024
6
×
DAC Gain
REFERENCE
in the resistor of
⎞
⎟
⎠
⎞
⎟
⎠
×
32
FS
is equal to
Rev. A | Page 39 of 60
0.1µF
35
30
25
20
15
10
VREF
5
0
10kΩ
I120
0
AD9776A/AD9778A/AD9779A
200
AD9776A/AD9778A/AD9779A
1.2V BAND GAP
Figure 76. I
Figure 75. Reference Circuitry
DAC GAIN CODE
400
FS
vs. DAC Gain Code
Q DAC GAIN
I DAC GAIN
CURRENT
SCALING
600
Q DAC
I DAC
800
DAC FULL-SCALE
REFERENCE
CURRENT
1000