Data Sheet

ADL9005

APPLICATIONS INFORMATION

analog.com

Rev. A | 22 of 24

PROVIDING DRAIN BIAS

The ADL9005 was characterized using a connectorized wideband

bias tee (Marki Microwave BT2-0040). In practice, the drain bias

must be provided by a board mountable component. Drain biasing

for a wideband amplifier, such as the ADL9005, is traditionally

provided by connecting a wideband conical inductor between

RFOUT/VDD and the 5 V power supply, as shown in Figure 74.

Conical inductors are fragile and physically large. Figure 76 shows

an alternative biasing circuit that uses 0402 sized, surface-mount

components. The gain, input return loss, and output return loss over

frequency are shown in Figure 77.

Figure 76. Surface-Mounted Bias Tee Schematic

Figure 77. Gain and Return Loss vs. Frequency Using the Surface-Mount

Bias Tee

The circuit consists of ferrite beads (FB1 and FB2), an ac coupling

capacitor (COUT), an inductor (L3), de-Q resistors (R3 and R4), and

bypass capacitors (C1 and C2).

The R3, R4, C1, and C2 decoupling components are used to

reduce the RF coupling and to filter out power supply noise. R3 and

R4 are de-Q resistors that can reduce frequency glitches caused by

interactions between the PCB and the decoupling capacitors.

FB2 is critical to achieving high frequency operation. Optimal per-

formance is achieved when FB2 touches down on the RF trace

directly. FB1 is also a critical component that must be placed as

close as possible to FB2 because a longer trace adds increased

inductance and capacitance. FB1 mitigates resonances caused by

the interaction between FB2 and the PCB.

The L3 inductor is only needed if operation at below 100 MHz is

required. Otherwise, omit L3.

Table 9 lists the part numbers of the manufacturers and values

used in the surface-mounted bias tee circuit shown in Figure 76.

Further details on design of surface-mount bias tee circuits can be

found in Application Note AN-2061.

Table 10. Part Numbers of the Manufacturers and Values Used in the Surface-Mounted Bias Tee Circuit Shown in Figure 76

Component

Value

Manufacturer

Part Number

FB1, FB2

470 Ω

Murata

BLM15GG471SN1D

L3

0.11 µH

Coilcraft

0805LS-111X_E_

COUT

100 nF

American Technical Ceramics

ATC 560L

R3

340 Ω

Panasonic

ERA-2AEB3400X

C1, C2

1 pF

Murata

GJM1555C1H1R0CB01D

R4

270 Ω

Panasonic

ERJ-2GEJ271X