RF3809PCK-415 查看數據表（PDF） - RF Micro Devices

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RF3809PCK-415

GaAs HBT PRE-DRIVER AMPLIFIER

RF Micro Devices 

RF3809

Theory of Operation and Application Information

RF3809 design accommodates use in a variety of applications:

• Linear driver from 450MHz to 2500MHz

• 2nd/3rd stage high linearity LNA, with noise figure in the 3dB to 4dB range from 800MHz to 2200MHz

• High efficiency (>50%) output stage for non-linear applications

Nominal data sheet shows specification for VCC=VBIAS=VREF=8V. RF3809 can easily be configured for 5V operation, with a

simple bias resistor change at VREF.. “Bias Table” on page 5 shows resistor values for VCC=VBIAS=VREF=5V. Generally speak-

ing, 5V data will compare to that for 8V as follows:

• 3dB to 3.5dB reduction in OP1dB

• 0.4dB to 0.5dB increase in small signal gain

For operation at other than 5V, bias R can be calculated as follows (VCC=VBIAS=VREF=5V is used here to illustrate, operation at

different voltage is determined with same methodology).

1. Use nominal 8V case as a starting point: VCC=VBIAS=VREF=8V, IREF =15mA, ICQ=258mA. Target condition will be to

achieve same ICQ with VCC=VBIAS=VREF=5V.

2. Using evaluation board with separate lab supplies on (VCC/VBIAS) and (VREF), set VCC/VBIAS=5V, VREF=8V. IREF is main-

tained at 15mA, and ICQ drops from nominal value of 258mA.

3. VREF can then be increased >8V until ICQ is restored. IREF increase to 23mA is required (as seen in “Bias Table” on page 5).

4. At this point, pin voltage at VREF is calculated (or measured with DVM): VPIN=VREF at eval board input – IREF*bias R=10.8–

0.023 * 300 = 3.9 V.

5. Next, calculate new bias R for VREF=5V: Bias R=(5–3.9)/0.023=47.8Ω. See “Bias Table” on page 5, standard resistor

value=47Ω is called out. In this way, bias R can be calculated for any VCC=VBIAS=VREF configuration. The maximum IREF

limit for RF3809=30mA.

Junction-to-case thermal resistance (RTH_JC) is shown versus output power in the graph section of this data sheet. The graph

was generated with nominal VCC=VBIAS=VREF=8V, IREF=15mA, where ambient temperature=85°C. Using this curve along

with operating condition, junction temperature can be calculated. Resultant TJ for this case yields MTTF≥100 years. Standard

RF3809 evaluation boards are matched for high efficiency at OP1dB. To ensure reliability for operation at high power, output

match achieving equivalent or better efficiency on system board should be the goal.

Typical s-parameter responses for each evaluation board are shown within the data sheet. These boards were matched with

two specifications in mind:

• Output load impedance set for optimum OIP3/ACP (Adjacent Channel Power for commonly used modulation standards).

• Output load impedance set for high efficiency at OP1dB, with ruggedness (survival) into output 4:1 VSWR.

In some cases, low power operation being one, it may be desirable to improve output return loss seen on evaluation board.

This can be done with output match adjust. The result will be an increase in small signal gain. Tradeoffs between return loss,

gain, OIP3, and compression point can then be considered in obtaining optimum performance for a particular application.

Finally, infrastructure qualification report for RF3809 can be obtained by contacting RFMD.

Rev A4 DS080221

7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical

support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.

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