RF3806 查看數據表（PDF） - RF Micro Devices

零件编号

产品描述 (功能)

生产厂家

RF3806

GaAs HBT PRE-DRIVER AMPLIFIER

RF Micro Devices 

RF3806

Theory of Operation

General biasing considerations can be described using RF3806 UMTS evaluation board as a reference. In actual system,

3

VCC=VBIAS=VREF can be tied together when PA is to remain biased on at all times. For non-constant operation, VCC is tied to

VBIAS, and VREF used for turn-on preceding transmit. Table is provided in data sheet for adjusting IREF to desired bias current for

various supply voltage levels (more detailed discussion below).

RF3806 can be used in frequency bands ranging from 1500MHz to 2200MHz. Depending on specific application, the follow-

ing parameters and their trade-offs can be considered: linearity, average output power, signal modulation/peak to average

ratio (PAR), efficiency, dissipated power, junction temperature (Tj), and wear out MTTF. Looking at two distinct examples will

demonstrate how the above mentioned parameters are taken into account. Note that much of the discussed performance can

be found in the data sheet area showing graphs.

First, consider a UMTS pico cell base station transmitter (case 1). Here RF3806 fills the role of final PA, operating from

21dBm-26dBm POUT. VCC can be run from 5V to 8V. Likewise, bias resistance on VREF line can be set to obtain IREF ranging

from 41mA -60mA. The choice of voltage supply and bias is determined by required W-CDMA ACPR spec, desired POUT, and sig-

nal PAR. For instance, consider the following: POUT=26dBm, frequency=2110MHz-2170MHz, signal=W-CDMA test model I

64 DPCH, ACPR requirement over temperature=-45dBc at 5MHz offset. The operating condition here (see data sheet graph

section) would be VCC=8V and IREF=60mA, using impedance match found on UMTS Evaluation Board. For a lower output

power requirement, IREF is kept at 60mA, and VCC reduced to a level below 8V. Sufficient linearity can be obtained at lower

POUT, while the decrease in dissipated power yields a lower junction temperature and enhanced MTTF. For thermal consider-

ations, refer to graphs provided for thermal resistance, junction temperature, and MTTF (these three graphs based on RF3806

thermal scan and process reliability data).

For the second example (case 2), consider a higher power application, where POUT=34dBm and linearity requirement is sub-

stantially reduced from that seen in above example. For this application, we might run IREF=41mA with VCC=8V. RF3806 out-

put load line would be set for maximum efficiency and compression point. The result is a transmit PA which obtains output

power spec, while providing high enough efficiency to keep Tj within desired range. Running IREF=41mA avoids unnecessary

power dissipation, as higher IREF is used only in lower power case for linearity enhancement. A DCS/PCS application schematic

is provided in data sheet for higher power applications, along with corresponding information in section containing graphs.

UMTS evaluation board can be converted to the application schematic, with minor changes to input, output, and interstage

matches (interstage @VCC1 pin). Also, bias resistors at VREF are scaled for lower IREF=41mA. EDGE ACP plots are provided in

the graph section. Note that the matching also covers transmit bands for 1850-1910 CDMA. As a result, this converted appli-

cation board could also be considered for CDMA booster/repeater.

As mentioned above, junction temperature is an important consideration when operating at maximum VCC (8V). The most

demanding scenario, case 1 above, will be considered here as an illustration. In the data sheet graph section, refer to graphs

of Tj vs POUT, RTH vs POUT, and RF3806 wear out MTTF vs Tj. During thermal scan, RF3806 eval board is affixed to a large, tem-

perature controlled stage, held at ambient. The device is etched open, such that thermal image of die can be taken. Reference

temperature is measured at evaluation board to stage interface by thermocouple, placed through a thin groove such that it

makes contact with underside eval board GND plane (directly beneath RF3806). Thermocouple measures "reference tempera-

ture", from which RTH_JREF (junction to reference) is determined. Evaluation board thermal resistance, RTH_BOARD, has been

modeled at 1°C/W. Knowing these two values allows us to calculate junction to case thermal resistance of

RF3806=RTH_JC=RTH_JREF-RTH_BOARD=RTH_JREF-1 (see graph). Thus, RTH_JC is defined as thermal resistance from junction to

GND slug of device.

3-120

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

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

Rev A3 DS070509

Share Link: