Analog Devices ADRV9002

UG-1828 Preliminary Technical Data
Rev. PrB | Page 234 of 277
1.8V COMMON
POWER PLAIN FEED
1.8V COMMON
POWER PLAIN FEED
TX2 SUPPLY
DOMAIN
(VANA2_1P8)
TX2 SUPPL
Y DOMAIN
(
VANA1_1P8)
LOO
P BETWEEN CENTRE
TA
P
BALUN /
EXTERNA
L
CHOKES AND TX POWER
DOMAINS NEEDS
TO BE KEPT SHOR
T.
24159-200
Figure 231. 1.8 V Transmitter Power Supply Routing on the ADRV9001 Evaluation Board
An example of the balun feed supply designed to achieve the isolation managed in the evaluation board is shown in Figure 231 and
Figure 232.
DC Balun
When a Tx balun that is able to conduct dc is used then the system shown in Figure 231 should be used. The decoupling cap near the Tx
balun should be placed as close as possible to the balun’s DC feed pin. Its orientation should be perpendicular to the ADRV9001 device
so the return current avoids a ground loop with the ground pins surrounding the Rx input. The customer card provides an option to
install an RF isolation inductor which can provide extra isolation between the Tx1 and Tx2 balun supply feeds. A 10µF capacitor and a
0.1 µF capacitor are helpful on the dc feed pin to eliminate Tx spectrum spurs and dampen the transients. Note that when this supply
approach is used the series matching components must be dc shorts. It is recommended to use 0 Ω if an inductor is not needed to match
the balun impedance to the Tx output impedance.
DC FEED FROM
VANA1/2_1P8 PLANE
RESER
VOIR
CA
PACITORS
OPTIONA
L RF
ISOLA
TION INDUCTOR
BALUN
RF BALUN SELECTION COMPONENTS.
DC CONTINUIT
Y ON DIFFERENTIAL SIDE
DECOUPLING
CA
PACIT
OR
(ORIEN
TATION IS
IMPOR
TANT)
24159-202
Figure 232. Transmitter Power Supply for a Balun with a Center Tap
Chokes
The ADRV9001 evaluation board provides flexibility to be configured to use a Tx balun that is not capable of conducting dc current. In
such a scenario, the user should install dc chokes as well as their decoupling capacitors as highlighted in Figure 232. Care should be taken
to match both chokes to avoid potential current spikes. Difference in parameters between both chokes can cause unwanted emission at
Tx outputs. Note that if the differential input to the balun can create a dc short to ground (through the balun), the series matching
components must be capacitors. If a short can form on the single-ended side, the single-end series blocking element must be a capacitor.