AD9779A-EBZ Analog Devices Inc, AD9779A-EBZ Datasheet - Page 39

• Manufacturer Part Number: AD9779A-EBZ
• Description: Dual 16B, 1.0 GSPS TxDAC
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9779A-EBZ

• Design Resources: Interfacing ADL5370 to AD9779A Dual-Channel, 1 GSPS High Speed DAC (CN0016) Interfacing ADL5371 to AD9779A Dual-Channel, 1 GSPS High Speed DAC (CN0017) Interfacing ADL5372 to AD9779A Dual-Channel, 1 GSPS High Speed DAC (CN0018) Interfacing ADL5373 to AD9779A Dual-Channel, 1 GSPS High Speed DAC (CN0019) Interfacing ADL5374 to AD9779A Dual-Channel, 1 GSPS High Speed DAC (CN0020) Interfacing ADL5375 to AD9779A Dual-Channel, 1 GSPS High Speed DAC (CN0021)
• Number Of Dac's: 2
• Number Of Bits: 16
• Outputs And Type: 2, Differential
• Sampling Rate (per Second): 1G
• Data Interface: Serial
• Dac Type: Current
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9779A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Settling Time: -
• 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