MRF89XA datasheet(97/140 Pages) MICROCHIP

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Preliminary

DS70000622D-page 97

MRF89XA

4.5.2

SUGGESTED PA BIASING AND

MATCHING

The recommended PA bias and matching circuit is

illustrated in Figure 4-5.

FIGURE 4-5:

RECOMMENDED PA BIASING AND OUTPUT MATCHING

Refer to Section 4.8, Bill of Materials for the opti-

mized matching arrangement for each frequency band.

4.5.3

COMMON INPUT AND OUTPUT

FRONT-END

The Receiver and Transmitter share the same RFIO

pin (pin 31). Figure 4-6 illustrates the configuration of

the common RF front-end.

In Transmit mode, the PA and the PA regulator are

active, with the voltage on the PARS pin equal to the

nominal voltage of the regulator (1.8V). The external

inductance is used to bias the PA.

In Receive mode, both the PA and the PA regulator are

OFF and PARS is tied to the ground. The RF choke

inductor is then used to bias the LNA.

FIGURE 4-6:

FRONT-END

DESCRIPTION

PARS

RFIO

100 nH

0.047 µF

SAW

Low-pass and DC block

Antenna

port

DC block

1W 1%

RFIO

PARS

RX ON

LNA

Antenna

Regulator

(1.8V)

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