UG-1828
Preliminary Technical Data
Rev. PrC | Page 262 of 338
Figure 251. ADRV9001 DC Bias Configuration for the Transmitter Output Using Wire-Wound Chokes
Figure 252. ADRV9001 DC Bias Configuration for the Transmitter Output Using a Center-Tapped Transformer
The ADRV9001 evaluation board provides flexibility to configure each Tx output to work with either a center tapped transformer (balun)
or a set of two closely matched wire wounded chokes. The center tapped transformer passes the bias voltage directly to the transmitter
outputs through each differential input. This configuration offers the lowest component count.
In some cases, the desired balun does not provide a dc connection to the transmitter output lines. To support this situation, the
ADRV9001 evaluation board provides the placeholders for RF chokes tied to the VANA1_1P8 (for Tx1 output) and VANA2_1P8 (for Tx2
output) supply. It also provides the placeholders for ac coupling capacitors to prevent creating a dc short through the balun to ground.
Impedance matching networks on the balun single-ended port are usually required to achieve optimum performance. In addition, ac
coupling is often required on the single-ended side if the balun contains a dc path from one of the transmitter’s differential outputs to the
single-ended port.
Careful planning is required for the Tx balun selection. If a Tx balun is selected that requires a set of external DC bias chokes, it is
necessary to find the optimum compromise between the choke physical size, choke dc resistance (RDCR) and the balun passband
insertion loss. Users should refer to the RF Port Interface Information section of this document for more information on Tx output balun
and RF choke selection as well as matching circuit recommendations.
TX Balun DC Supply Options
Each transmitter requires approximately 200 mA supplied through an external connection. The PCB layout of the ADRV9001 board
allows use of external chokes to provide 1.8 V power domain to the ADRV9001 outputs to allow users to try different baluns that may not
have a dc center tap pin to supply the bias voltage to the transmitter outputs.
To reduce switching transients when attenuation settings change, the balun dc feed should be powered directly by the 1.8 V plane. The
geometry of the 1.8 V plane should be designed so that each balun or each pair of chokes is associated with its Tx output. The
VANA1_1P8 should be used to power Tx1 output and VANA2_1P8 should be used to power Tx2 output.
If careful layout and isolation of the dc supply is not followed, it can adversely affect Tx-Tx isolation. Figure 253 shows the power supply
layout configuration used on the ADRV9001 board to achieve the desired Tx-Tx isolation performance. This image illustrates star
connection from common 1.8 V analog power plane.
V
DC
= 1.8V
C
B
R
DCR
ΔV
V
BIAS
=
1.8V – ΔV
V
BIAS
=
1.8V – ΔV
ΔV
R
DCR
L
C
+
–
+
–
L
C
OUTPUT
STAGE
I
BIAS
= ~100mA
I
BIAS
= ~100mA
24159-
294
Tx1–/Tx2–
Tx1+/Tx2+
ΔV
V
BIAS
=
1.8V – ΔV
V
BIAS
=
1.8V – ΔV
+
–
ΔV
+
–
C
B
Tx1 OR Tx2
OUTPUT
STAGE
I
BIAS
= ~100mA
1.8V
R
DCR
R
DCR
I
BIAS
= ~100mA
24159-
295
Tx1–/Tx2–
Tx1+/Tx2+
