MRFIC1807 データシートの表示（PDF） - Motorola => Freescale

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MRFIC1807

1.8 GHz Power Amp/Switch

Motorola => Freescale 

DESIGN AND APPLICATIONS INFORMATION

DESIGN PHILOSOPHY

The MRFIC1807 is designed to operate with the MRFIC1806

Driver/Ramp IC in 1.9 GHz Personal Communication System

(PCS) applications such as Europe’s DECT and Japan’s PHS.

The design incorporates a depletion mode GaAs power MES-

FET with a high–power transmit/receive switch and

associated bias circuitry in one low–cost SOIC–16 package.

The power MESFET is sized to produce at least 27 dBm

saturated output power, including switch loss, from a 3.5 V

supply, but the output power can be controlled using the

PCNTRL input. This control voltage also allows setting of the

quiescent current of the FET. PCNTRL can be set to give

best efficiency or linearity for the particular system application.

The TX/RX control pin allows fast switching of the T/R switch

for TDMA applications. When switching from transmit to

receive, the battery supply voltage should be removed from

the PA (Pin 4), to avoid excessive current drain. This is usu-

ally accomplished using an external pass transistor con-

trolled by the TX/RX signal. Alternatively, if PCNTRL is

reduced to 0 V during RX mode, the bias current is reduced

to nearly zero.

The Transmit/Receive switch is a reflective MESFET

design which is optimized for low loss and power handling in

transmit mode. The design can handle 28 dBm of transmit

power without significant increase in insertion loss. A regu-

lated 3.0 Volt supply is required at pin 16 for the T/R switch

and the bias and control circuitry.

DECT APPLICATIONS

Figure 2 shows the component values for a DECT imple-

mentation of the MRFIC1807. For use in equipment designed

for DECT, the power amplifier is operated close to saturation

to improve device efficiency. Maximum power output at the

antenna connector is 24 dBm during a burst. The constant en-

velope characteristics of the GMSK modulation allow non–lin-

ear amplification without spectral regrowth. The transmit

signal must be shaped or “ramped” to meet system transmit

turn on time requirements of 10 msec minimum while not splat-

tering into adjacent channels. A turn on time on greater than

2.0 msec has been shown to give adequate adjacent channel

power performance. Most DECT realizations have the modu-

lation applied to the transmit VCO so the most straight for-

ward way of implementing this ramping function is at the

power amplifier. The MRFIC1806 Driver/Ramp IC has an

on–chip ramping circuit specifically designed for DECT.

When ramped in this manner, the MRFIC1806 will supply the

appropriately ramped RF signal to the MRFIC1807 which

only has to be turned on and off with TX/RX. Alternate off–

chip ramping can be implemented either with external com-

ponents or at baseband. Consult the MRFIC1806 datasheet

for more information.

PHS APPLICATIONS

For Japan’s Personal Handy System applications, the

modulation is p/4 DQPSK. When amplified with a non–linear

amplifier, the signal will regrow the sidebands which have

been carefully filtered at baseband, resulting in adjacent

channel interference. To avoid this spectral regrowth, the

amplifier must be operated “backed off” from saturation. The

amount of backoff required has been shown to be a function

of amplifier saturated output capability and may be as high

as 5.0 dB. The PHS specification calls for a maximum aver-

age power during a burst to be 19 dBm. This is consistent

with 5.0 dB backoff from the DECT operating point so the

same DECT operating condition could be used. Alternatively,

PCNTRL can be adjusted for a lower bias point to improve

efficiency or higher bias for better linearity. With p/4 DQPSK

modulation, ramping can be accomplished in the encoder so

no external ramp circuit is needed. See the MRFIC1806 data

sheet for further details.

EVALUATION BOARDS

Evaluation boards are available for RF Monolithic Inte-

grated Circuits by adding a “TF” suffix to the device type.

For a complete list of currently available boards and ones

in development for newly introduced product, please con-

tact your local Motorola Distributor or Sales Office.

MOTOROLA RF DEVICE DATA

MRFIC1807

7

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