Motorola A008 Service Manual page 50

A008 / A6188+ – Circuit Description
18) PA matching is achieved using the
GSM_PINDIODE (-5V
tuning stubs within the MCIC to provide correct matching. The
samples off part of the transmitted power to feed back to the
19) The signal now goes through FL1000, FL1000 is a low pass filter, filtering 2
harmonics of GSM and DCS frequencies.
20) The amplified signal is then fed through to the
controlled as was discussed in Receive, then passed to the
Socket Switch J600
RF: Power Control Operation
1) The PAC IC U350
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 Q370.
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.
5) EXC Pin 7.This output drives the power control port of the exciter. An increase of
this voltage will cause the exciter to increase its output power.
6) SAT_DET Pin 12. If the feedback signal from the RF detector lags too far behind the
AOC signal then this output will go low, indicating that the loop in at or near
saturation. This signals the DSP to reduce the
rises. See Fig 6.1
7) AOC_DRIVE Pin 8. The voltage on this pin will determine the output power of the
transmitter. Under normal conditions the control loop will adjust the voltage on EXC
so that the power level presented to the RF detector results in equality of the voltage
present at INT and AOC. The input level will be between 0 and 2.5V.
8) ACT Pin 9. This pin will hold a high voltage when no RF is present. Once the RF
level increases enough to cause the detector to rise a few millivolts then this output
will go low. In the GSM radio a resistor is routed between this point and the AOC
input to cause the radio to ramp up the power until the detector goes active.
Motorola Internal Use
MCIC Filter FL300
and DCS_SEL
(Power Amplifier Control Integrated Circuit) controls the power
Pin 2) provides a DC level proportional to the peak RF
DET_SW
and the signal
through Q322). The signal switches in or out
PAC IC U340
RF switch U101, which again is
Antenna A1/ Accessory
is high (floating).
AOC_DRIVE signal until
7
MCIC filter also
nd rd
and 3
SAT_DET