Motorola P8190 Service Manual Page 112

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TDMA StarTAC
TM
P8190 : Am p D r i v e r s
TX_800
FL452
FL454
DRIVER_B+
Q475-A
Q401
800KEY
CR810-B
TX_800
CR810-A
TX_2.75
Q810
800BIAS
Q811
A_D
R811
Description
After the desired transmit information is modulated with a TX carrier frequency, enough signal power needs to be provided for RF transmission through the antenna. The
driver stage is used to relieve amplification of the final stage PA. This reduces excess heat dissipation and overloading of the final stage PA.
The TX signal passes through FL452 and then is amplified by Q401. Q401 is driven on by suppling DRIVER_B+ through Q475-A. Q475-A can be switched on or off via
the 800KEY line. A low state 800KEY brings the gate of Q475-A to a low level, causing Q475-A to switch on.
There are two operating modes in this unit, which are analog and digital. The output of Q810 is used to provide the biasing voltage for the final stage PA(U801). Q810 is
switched on by having a low level at the gate.
The 800BIAS voltage level determines the operating condition of the final stage PA. A lower voltage level at 800BIAS denotes digital mode and a higher voltage level
denotes analog mode. In analog mode, A_D is pulled high causing Q811 to be switched off. This state causes a voltage drop across R811, thus, having a lower voltage
level at 800BIAS. In digital mode A_D is pulled low causing Q811 to be switched on. During this state R811 is bypassed and 800BIAS will have a higher voltage level.
A14
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