AD9705 Analog Devices, AD9705 Datasheet - Page 34

• Manufacturer Part Number: AD9705
• Manufacturer: Analog Devices

Specifications of AD9705

• Resolution (bits): 10bit
• Dac Update Rate: 175MSPS
• Dac Settling Time: 11ns
• Max Pos Supply (v): +3.6V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Par

AD9704/AD9705/AD9706/AD9707
Table 20. MEMRDWR—Register 0x0F
Mnemonic
CALSTAT
CALEN
SMEMWR
SMEMRD
UNCAL
Table 21. MEMADDR—Register 0x10
Mnemonic
MEMADDR[5:0]
Table 22. MEMDATA—Register 0x11
Mnemonic
MEMDATA[5:0]
REFERENCE OPERATION
The
band gap reference. The internal reference can be disabled by
writing a Logic 1 to Register 0x00, Bit 0 (EXREF) in the SPI.
To use the internal reference, decouple the REFIO pin to ACOM
with a 0.1 μF capacitor, enable the internal reference by writing
a Logic 0 to Register 0x00, Bit 0 in the SPI. (Note that this is the
default configuration.) The internal reference voltage is present
at REFIO. If the voltage at REFIO is to be used anywhere else in
the circuit, an external buffer amplifier with an input bias current of
less than 100 nA must be used to avoid loading the reference. An
example of the use of the internal reference is shown in Figure 78.
REFIO serves as either an input or an output, depending on
whether the internal or an external reference is used. Table 23
summarizes the reference operation.
Table 23. Reference Operation
Reference
Mode
Internal
External
AD9704/AD9705/AD9706/AD9707
0.1µF
AVSS
R
FS ADJ
REFIO Pin
Connect 0.1 μF capacitor
Apply external reference
SET
Figure 78. Internal Reference Configuration
REFIO
Bit No.
[5:0]
Bit No.
[5:0]
I
Bit No.
7
6
3
2
0
REF
V
1.0V
BG
AD9704/AD9705/
AD9706/AD9707
–
+
I/O
Direction (I/O)
Direction (I/O)
O
I
I
I
I
Direction (I/O)
I/O
CURRENT
SCALING
x32
contain an internal 1.0 V
Register Setting
Register 0x00, Bit 0 = 0
(default)
Register 0x00, Bit 0 = 1
(for power saving)
I
OUTFS
DAC
Default
111111
Default
000000
Default
0
0
0
0
0
Rev. B | Page 34 of 44
Description
Data for static memory access
Description
1 = calibration cycle complete
1 = initiates device self-calibration
1 = writes to static memory (calibration coefficients)
1 = reads from static memory (calibration coefficients)
1 = resets calibration coefficients to default (uncalibrated)
Description
Address of static memory to be accessed
An external reference can be used in applications requiring
tighter gain tolerances or lower temperature drift. Also, a variable
external voltage reference can be used to implement a method
for gain control of the DAC output. The external reference is
applied to the REFIO pin. Note that the 0.1 μF compensation
capacitor is not required. The internal reference can be directly
overdriven by the external reference, or the internal reference
can be powered down. The input impedance of REFIO is 10 kΩ
when powered up and 1 MΩ when powered down.
REFERENCE CONTROL AMPLIFIER
The
amplifier that regulates the full-scale output current, I
control amplifier is configured as a V-I converter, as shown in
Figure 78. The output current, I
the V
I
proper scale factor to set I
The control amplifier allows a 5:1 adjustment span of I
1 mA to 5 mA by setting I
(R
I
power dissipation of the AD9704/AD9705/AD9706/ AD9707,
which is proportional to I
The second benefit relates to the ability to adjust the output over a
14 dB range, which is useful for controlling the transmitted power.
REF
OUTFS
SET
is mirrored to the segmented current sources with the
AD9704/AD9705/AD9706/AD9707
between 6.4 kΩ and 32 kΩ). The wide adjustment span of
REFIO
provides several benefits. The first relates directly to the
and an external resistor, R
OUTFS
OUTFS
REF
between 31.25 μA and 156.25 μA
(see the Power Dissipation section).
, as stated in Equation 3.
REF
, is determined by the ratio of
SET
, as stated in Equation 4.
contain a control
Data Sheet
OUTFS
OUTFS
from
. The