Data Sheet

ADL8121

APPLICATIONS INFORMATION

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Rev. A | 19 of 22

The basic connections for operating the ADL8121 over the

specified frequency range are shown in Figure 78. AC-couple

the input and output of the ADL8121 with appropriately sized

capacitors (such as American Technical Ceramics Part Number

531Z104KTR16T).

A 5 V dc bias is supplied to the amplifier through the choke inductor

connected to the RFOUT/VDD pin. The recommended bias inductor

is the Murata

® ferrite bead BL15GG471SZ1D, 470 Ω.

The bias conditions, VDD = 5 V and IDQ = 95 mA, are the recom-

mended operating point to achieve optimum performance. To set

other bias conditions, adjust the value of RBIAS. Table 7 shows the

recommended RBIAS values and their associated IDQ values.

Table 7. Recommended Bias Resistor Values for VDD = 5 V

RBIAS (Ω)

IDQ (mA)

IDQ_AMP (mA)

IRBIAS (mA)

2800

25

24

1.0

1800

35

33.6

1.4

970

55

51.8

3.2

560

75

70.9

4.1

324

95

90.1

4.9

130

115

109.7

5.3

The shunt resistor, inductor, capacitor (RLC) network on the input

of the ADL8121 adds resistive loss to help stabilize the amplifier

by reducing the gain at low frequencies. The shunt inductor makes

the resistor frequency dependent. At low frequencies, the resistor

becomes more active. The resistor has less influence at higher fre-

quencies where the impedance of the choke is high. The capacitor

blocks dc voltages and currents from flowing through the resistor

and the inductor.

To achieve optimal performance from the ADL8121, it is critical

to supply low inductance ground connections to the GND pins as

well as to the backside exposed pad to ensure stable operation.

To prevent damage to the device, do not exceed the absolute

maximum ratings (see Table 3).

Figure 78. Typical Application Circuit