MRFIC0917 查看數據表（PDF） - Motorola => Freescale

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MRFIC0917

900 MHz GSM CELLULAR INTEGRATED POWER AMPLIFIER GaAs MONOLITHIC INTEGRATED CIRCUIT

Motorola => Freescale 

APPLICATIONS INFORMATION

Design Philosophy

The MRFIC0917 is a two–stage Integrated Power Amplifier

designed for use in cellular phones, especially for those used

in GSM Class IV, 3.6 V operation. Due to the fact that the in-

put, output and some of the interstage matching is accom-

plished off chip, the device can be tuned to operate anywhere

within the 800 to 1000 MHz frequency range.

This capability makes the MRFIC0917 suitable for portable

cellular applications such as:

S

3.6 V 900 MHz DAMPS

S

3.6 V 900 MHz PDC

RF Circuit Considerations

The MRFIC0917 can be tuned by changing the values and/

or positions of the appropriate external components. Refer to

Figure 2, a typical GSM Class IV applications circuit.

The input match is a shunt–C, series–L, low–pass structure

and can be retuned as desired with the only limitation being the

on–chip 12 pF blocking capacitor. For saturated applications

such as GSM and analog cellular, the input match should be

optimized at the rated RF input power.

Interstage matching can be optimized by changing the value

and/or position of the decoupling capacitor on the VD1 supply

line. Moving the capacitor closer to the device or reducing the

value increases the frequency of resonance with the induc-

tance of the device’s wirebonds and leadframe pin.

Output matching is accomplished with a two–stage low–pass

network as a compromise between bandwidth and harmonic

rejection. Implementation is through chip capacitors mounted

along a 30 or 50Ω microstrip transmission line. Values and

positions are chosen to present a 2Ω loadline to the device

while conjugating the device output parasitics. The network

must also properly terminate the second and third harmonics to

optimize efficiency and reduce harmonic output. When low–Q

commercial chip capacitors are used for the shunt capacitors,

loss can be reduced by mounting two capacitors in parallel to

achieve the total value needed.

Loss in circuit traces must also be considered. The output

transmission line and the bias supply lines should be at least

0.6 mm in width to accommodate the peak circulating currents

which can be as high as 2 amperes. The bias supply line which

supplies the output should include an RF choke of at least 8

nH, surface mount solenoid inductors or equivalent length of

microstrip lines. Discrete inductors will usually give better effi-

ciency and conserve board space.

The DC blocking capacitor required at the output of the de-

vice is best mounted at the 50Ω impedance point in the circuit

where the RF current is at a minimum and the capacitor loss

will have less effect.

Power Control Using the MC33169

The MC33169 is a dedicated GaAs power amplifier support

IC which provides the –4 V required for VSS, an N–MOS drain

switch interface and driver and power supply sequencing. The

MC33169 can be used for power control in applications where

the amplifier is operated in saturation since the output power

in non–linear operation is proportional to VD2. This provides a

very linear and repeatable power control transfer function.

This technique can be used open–loop to achieve 20–25 dB

dynamic range over process and temperature variation. With

careful design and selection of calibration points, this tech-

nique can be used for GSM phase II control where 29 dB dy-

namic range is required, eliminating the need for the

complexity and cost of closed–loop control.

The transmit waveform ramping function required for sys-

tems such as GSM can be implemented with a simple Sallen

and Key filter on the MC33169 control loop. The amplifier is

then ramped on as the VRAMP pin is taken from 0 V to 3 V. To

implement the different power steps required for GSM, the

VRAMP pin is ramped between 0 V and the appropriate voltage

between 0 V and 3 V for the desired output power.

For closed–loop configurations using the MC33169,

MMSF4N01HD N–MOS switch and the MRFIC0917 provide a

typical 1 MHz 3 dB loop bandwidth. The STANDBY pin must

be enabled (3 V) at least 800 µs before the VRAMP pin goes

high and disabled (0 V) at least 20 µs before the VRAMP pin

goes low. This STANDBY function allows for the enabling of

the MC33169 one burst before the active burst thus reducing

power consumption.

Biasing Considerations

Gate bias is supplied to each stage separately through resis-

tive division of the VSS voltage. The top of each divider is brought

out through pins 12 and 13 (VG2 and VG1 respectively) allowing

gate biasing through use of external resistors or positive volt-

ages. This allows setting the quiescent current of each stage

separately.

For applications where the amplifier is operated close to

saturation, such as GSM and analog cellular, the gate bias

can be set with resistors. Variations in process and tempera-

ture will not affect amplifier performance significantly in these

applications. The values shown in the Figure 1 will set quies-

cent currents of 100 to 200 mA for the first stage and 600 to

1200 mA for the second stage.

For linear modes of operation, the quiescent current must

be more carefully controlled. For these applications, the VG

pins can be referenced to some tunable voltage which is set at

the time of radio manufacturing. Less than 1.0 mA is required

in the divider network so a DAC can be used as the voltage

source. Typical settings for 3.6 V linear operation are 150 mA

±5% for the first stage, and 750 mA ±5% for the second stage.

Conclusion

The MRFIC0917 offers the flexibility in matching circuitry and

gate biasing required for portable cellular applications. Together

with the MC33169 support IC, the device offers an efficient sys-

tem solution for TDMA applications such as GSM where satu-

rated amplifier operation is used.

Evaluation Boards

Evaluation boards are available for RF Monolithic Inte-

grated Circuits. For a complete list of currently available

boards and ones in development for newly introduced

product, please contact your local Motorola Distributor or

Sales Office.

MOTOROLA RF DEVICE DATA

MRFIC0917

9

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