UG-1828
Preliminary Technical Data
Rev. PrC | Page 234 of 338
S parameters for a selected balun and ac-coupling SMD type caps and ADRV9001 RX input impedance can be used to represent balun’s
balanced side interface to the device. Shunt and series matching component can be added with short TLs to represent possible PCB traces
associated with these matching components on the single side of balun. Peaking of return loss at 2.5 GHz looking into the single-ended
interface of balun has been reduced by a clockwise rotation of high frequency portion of S11 curve on the Smith chart by adding a shunt
capacitor followed by series inductor after short transmission lines away from the balun’s single-ended terminal.
GENERAL TRANSMITTER BIAS AND PORT INTERFACE
This section considers the dc biasing of the ADRV9001 transmitter (Tx) outputs and how to interface to each Tx port. ADRV9001
transmitters operate over a range of frequencies. At full output power, each differential output side draws approximately 100mA of DC
bias current. The Tx outputs are DC biased to a 1.8 V supply voltage using either RF chokes (wire-wound inductors) or a transformer
center tap connection.
Careful design of the dc bias network is required to ensure optimal RF performance levels. When designing the dc bias network, select
components with low dc resistance (R
DCR
) to minimize the voltage drop across the series parasitic resistance element with either of the
suggested dc bias schemes suggested in Figure 218. The R
DCR
resistors indicate the parasitic elements. As the impedance of the parasitics
increase, the voltage drop (ΔV) across the parasitic element increases causing the transmitter RF performance (that is, PO 1 dB PO MAX,
and so forth) to degrade. The choke inductance (LC) should be selected high enough relative to the load impedance such that it does not
degrade the output power.
The recommended dc bias network is shown in Figure 219. This network has fewer parasitic and fewer total components.
Figure 218. ADRV9001 RF DC Bias Configurations Depicting Parasitic Losses Due to Wire Wound Chokes
Figure 219. ADRV9001 RF DC Bias Configurations Depicting Parasitic Losses Due to Center Tapped Transformers
Figure 220 to Figure 223 identify four basic differential transmitter output configurations. Impedance matching networks (balun single-
ended port) are most likely to be required to achieve optimum device performance from ADRV9001. Also, the transmitter outputs must
be ac-coupled in most applications due to the dc bias voltage applied to the differential output lines of the transmitter.
The recommended RF transmitter interface is shown in Figure 220 featuring a center tapped balun. This configuration offers the lowest
component count of the options presented.
Brief descriptions of the transmitter port interface schemes are provided as follows.
•
Center tapped transformer passes the bias voltage directly to the transmitter outputs
•
RF chokes are used to bias the differential transmitter output lines. Additional coupling capacitors (CC) are added in the creation of a
transmission line balun
•
RF chokes are used to bias the differential transmitter output lines and connect into a transformer
•
RF chokes are used to bias the differential output lines that are ac-coupled into the input of a driver amplifier
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
Tx1–/Tx2–
Tx1+/Tx2+
24159-
168
I
BIAS
= ~100mA
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
Tx1–/Tx2–
Tx1+/Tx2+
