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P7389i – Circuit Description
Support Voltage being
14) The signal is then fed out through a buffer amplifier Q330, which is supported by
TX275.
The signal is also split with a sample of the output frequency being directed
back to the
MAGIC DM IC
part of the TX Phase Locked Loop.
15) To prevent the output frequency from the TX VCO before stabilisation has occurred,
being amplified and transmitted, there is an
biased 'on' by the exciter voltage from the
IC) Pin 7; this allows the TX output frequency through to the
and at same time gives more or less drive to the exciter stage.
16) The signal is then fed to a wide bandwidth
voltage from the PAC IC, and supported by a –ve biasing voltage created and timed
by
TX275 (RF_V2 + TX_EN
(Whitecap U800
Pin E2). Also supported by the voltage
through Q380)
17) PA matching is provided using the signals
Q1101) and TX_DCS
diodes
CR300
through
the inductive strips on the PCB.
18) The amplified signal is then fed back to the
then either transmitted through the
Pin 2
RF:
Power Control Operation
1) The
PAC IC U390
control of the transmitter. Below is a list of the main signals associated with the PAC
IC and their purposes.
2) The RF detector
(RF_IN
voltage out of the power amplifier, this is taken via an inductive strip from the output
of the PA U300.
3)
DET_SW
Pin 11. This pin controls the variable gain stage connected between the RF
detector and the integrator. The gain of the variable stage will be unity when
DET_SW
is low and will be 3 when
4)
TX_KEY
Pin 10. This signal is used to 'pre-charge' the Exciter and P.A. and occurs
20µS before the start of the transmit pulse.
Motorola Internal Use
SF_OUT
(MAGIC DM
Pin A3, for use within the TIC part of the MAGIC DM as
through Q120),
(TX275 + *DCS_SEL
CR306
to match the PA between GSM and DCS / PCS using
antenna A1
(Power Amplifier Control Integrated Circuit) controls the power
Pin 2) provides a DC level proportional to the peak RF
DET_SW
Pin C1)
Isolation Diode CR330
PAC IC U390
(Power Amplifier Control
Exciter Amplifier Q331
PA
U300, this is driven by the exciter
Filtered –5V
(-5V) and
PA B+ (DM_CS + B+
TX_GSM (TX275 + *GSM_SEL
through Q1101) to switch on or off the
RF switch
U150, as discussed in Receive,
or the
Accessory Socket RF Port J600
is high (floating).
7
placed. This is
DM_CS
through
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