General Transmitter Bias And Port Interface - Analog Devices ADRV9005 Reference Manual

Reference Manual
RF PORT INTERFACE INFORMATION
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GENERAL TRANSMITTER BIAS AND PORT INTERFACE

This section considers the DC biasing of the ADRV9001 transmitter outputs and how to interface with each transmitter port. The ADRV9001
transmitters operate over a range of frequencies. Each differential output side draws approximately 100mA of DC bias current at full output
power. The transmitter 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 ensures optimal RF performance levels. When designing the DC bias network, select components
with low DC resistance (R ) to minimize the voltage drop across the series parasitic resistance element, with either of the suggested DC
DCR
bias schemes suggested in Figure
voltage drop (ΔV) across the parasitic element increases, causing the transmitter RF performance (i.e., PO 1 dB PO MAX, and so forth) to
degrade. Select the choke inductance (LC) high enough relative to the load impedance such that it does not degrade the output power.
Figure 255 shows the recommended DC bias network. This network has fewer parasitic and total components.
Figure 254. ADRV9001 RF DC Bias Configurations Depicting Parasitic Losses Due to Wire Wound Chokes
Figure 255. ADRV9001 RF DC Bias Configurations Depicting Parasitic Losses Due to Center Tapped Transformers
Figure 256 , Figure 257, Figure
networks (balun single-ended port) are most likely required to achieve optimum device performance from the 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.
Figure 256 shows the recommended RF transmitter interface featuring a center-tapped balun. This configuration offers the lowest component
count of the available options.
The transmitter port interface schemes are briefly described 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.
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254. The R resistors indicate the parasitic elements. As the impedance of the parasitics increases, the
DCR
258, and Figure 259 identify four basic differential transmitter output configurations. Impedance matching
ADRV9001
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