Motorola Timeport P8190, Service Manual

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TDMA StarTAC
TM
P8190
: Merlin TX(U301)
U301
Merlin
TX_I
TX_Q
FM
Main VCO
Offset Oscillator
800*_1900
800
1900
TX_STEP
U110
ZIFSYN
U1700
IQ
Mod
AOC_CNTL
U1800
DCI
A_D
Not Used
Description
U301 is a TX modulator. It takes the TX information and modulates it on a carrier for RF transmission.
In analog mode the offset oscillator with the FM enters U301 and gets mixed with the main VCO. The resulting signal is a differential carrier with the modulated
information. The carrier is then passed through an IQ modulator. The A_D line controls the state of the IQ modulator. In analog mode, the IQ modulator simply feeds the
carrier through to a voltage controlled amplifier (VCA). The gain of the VCA is controlled via the AOC_CNTL line, therefore, controlling the TX power steps of the
transceiver. Once the carrier passes through the VCA, it passes through the cellular final power amplifier which is still internal to U301.
In digital mode the offset oscillator doesn‘t contain the modulated information from the FM line. The offset oscillator is mixed with the main VCO and a differential out-
put signal is sent through the IQ modulator. In digital mode, the A_D line configures the IQ modulator to allow IQ modulation to the carrier. The result carrier signal is
then passed through the Voltage Controlled Amplifier(VCA). The gain of the VCA is adjusted by the AOC_CNTL line, thus controlling the TX digital power steps of the
transceiver. Once the carrier passes through the VCA, it passes through the cellular final power amplifier and out to the transmit circuit.
The 800*_1900 line is used to enable or disable the final power amplifier.
The TX_STEP line is used to control the biasing to the cellular final amplifier. This line is used as a course gain control for the final amplifiers.
A
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