AD9772EB Analog Devices, AD9772EB Datasheet - Page 21

• Manufacturer Part Number: AD9772EB
• Description: 14-Bit/ 160 MSPS TxDAC+ with 2x Interpolation Filter
• Manufacturer: Analog Devices

Maintaining low noise on power supplies and ground is critical
to obtain optimum results from the AD9772. If properly
implemented, ground planes can perform a host of functions on
high speed circuit boards: bypassing, shielding current trans-
port, etc. In mixed signal design, the analog and digital portions
of the board should be distinct from each other, with the analog
ground plane confined to the areas covering the analog signal
traces, and the digital ground plane confined to areas covering
the digital interconnects.
All analog ground pins of the DAC, reference and other analog
components should be tied directly to the analog ground plane.
The two ground planes should be connected by a path 1/8 to
1/4 inch wide underneath or within 1/2 inch of the DAC to
maintain optimum performance. Care should be taken to ensure
that the ground plane is uninterrupted over crucial signal paths.
On the digital side, this includes the digital input lines running
to the DAC. On the analog side, this includes the DAC output
signal, reference signal and the supply feeders.
The use of wide runs or planes in the routing of power lines is
also recommended. This serves the dual role of providing a low
series impedance power supply to the part, as well as providing
some “free” capacitive decoupling to the appropriate ground
plane. It is essential that care be taken in the layout of signal and
power ground interconnects to avoid inducing extraneous volt-
age drops in the signal ground paths. It is recommended that all
connections be short, direct and as physically close to the pack-
age as possible in order to minimize the sharing of conduction
paths between different currents. When runs exceed an inch in
length, strip line techniques with proper termination resistors
should be considered. The necessity and value of this resistor
will be dependent upon the logic family used.
For a more detailed discussion of the implementation and con-
struction of high speed, mixed signal printed circuit boards,
refer to Analog Devices’ application notes AN-280 and AN-333.
REV. 0
TTL/CMOS
CIRCUITS
LOGIC
POWER SUPPLY
+3.0V OR +3.3V
Figure 46. Differential LC Filter for +3 V or 3.3 V
Applications
FERRITE
BEADS
+
–
100 F
ELECTROLYTIC
+
–
10 F–22 F
TANTALUM
0.1 F
CERAMIC
AVDD
ACOM
–21–
APPLICATIONS
MULTICARRIER
The AD9772’s wide dynamic range performance makes it well
suited for next generation base station applications in which it
reconstructs multiple modulated carriers over a designated
frequency band. Cellular multicarrier and multimode radios are
often referred to as software radios since the carrier tuning and
modulation scheme is software programmable and performed
digitally. The AD9772 is the recommended TxDAC in Analog
Device’s Softcell chipset which comprises the AD6622, Quadra-
ture Digital Upconverter IC, along with its companion Rx Digi-
tal Downconverter IC, the AD6624, and 14-bit, 65 MSPS
ADC, the AD6644. Figure 47 shows a generic software radio
Tx signal chain based on the AD9772/AD6622.
Figure 48 shows a spectral plot of the AD9772 operating at
64.54 MSPS reconstructing eight IS-136 modulated carriers
spread over a 25 MHz band. For this particular test scenario,
the AD9772 exhibited 74 dBc SFDR performance along with a
carrier-to-noise ratio (CNR) of 73 dB. Figure 49 shows a spec-
tral plot of the AD9772 operating at 52 MSPS reconstructing
four equal GSM carriers spread over a 15 MHz band. The
SFDR and CNR (in 100 kHz BW) measured to be 76 dBc and
83.4 dB respectively along with a channel power of –13.5 dBFS.
Note, the test vectors were generated using Rohde & Schwarz’s
WinIQSIM software.
Figure 48. Spectral Plot of AD9772 Reconstructing
Eight IS-136 Modulated Carriers @ f
PLLVDD = 0
Figure 47. Generic Multicarrier Signal Chain Using the
AD6622 and AD9772
SPORT
SPORT
SPORT
SPORT
AD6622
–100
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
JTAG
0
RCF
RCF
RCF
RCF
FILTER
FILTER
FILTER
FILTER
5
CIC
CIC
CIC
CIC
PORT
QAM
QAM
QAM
QAM
10
NCO
NCO
NCO
NCO
FREQUENCY – MHz
SUMMATION
15
20
CLK
DATA
25
PLLLOCK
OTHER AD6622's FOR
INCREASED CHANNEL
CAPACITY
= 64.54 MSPS,
AD9772
AD9772
30
CLK
35