Only For Training And Service Purposes - LG KS10 Service Manual

3. TECHNICAL BRIEF
3.5.6 Dual band GSM power amplifier (U501)
The TQM7M5003 is a high-power, high-efficiency power amplifier module with integrated power
control that provides over 50dB of control range. The devices is a self-contained 6mm°ø6mm module
with 50Ω input and output terminals. The device is designed for use as the final RF amplifier in
GSM850, EGSM900, DCS and PCS hand-held digital celluar equipment and other applications in the
824MHz to 849MHz, 880MHz to 915MHz, 1710MHz to 1785MHz and 1850MHz to 1910MHz bands.
The VBATT pin connects to an internal current-sense resistor and interfaces to an integrated power
amplifier control function, which is insensitive to variations in temperature, power supply, process, and
input power. The ENABLE input allows initial turn-on of PAM circuitry to minimize battery drain.
3.5.7 GSM transmit VCO (U502)
The dual Tx VCO is a key component within the GSM OPLL. This VCO performance directly impacts
PLL and transmitter performance. VCO specifications refer to muRata MQW5V0C869M datasheet.
The dual Tx VCO outputs, one for Low-band GSM and one for high band, drive a resistive network
that splits the active signal into two signals: 1) the input to the active PA . this is the low loss path,
and 2) the OPLL feedback signal . this is the high loss path. See Figure 8-1 for recommended
topology and resistor values.
The losses from the VCO outputs to the PA inputs must be factored into the output chain.s power
budget. Each path includes a π-pad that introduces approximately a 3-dB loss. The low band GSM
π-pad is formed by R516 plus R522, R521, and R524; the high band GSM π-pad is formed by R518
plus R523, R520, and R524. One leg of each π-pad is used to couple the VCO output to form the
feedback path as described below.
For a given VCO output drive level, the loss to the RTR6250 input must assure the specified input
level is achieved (-18 to -12 dBm). Large resistors included in the π-pads are used to lightly couple
off the VCO outputs to create the feedback signal. Since the RTR6250 TX_VCO_FB pin presents
fairly high impedance. A series capacitor (82 pF) AC couples the feedback signal into the RTR6250
IC.
LGE Internal Use Only
Figure 1.5.6-1 GSM PA functional block diagram
- 32 -
Copyright © 2007 LG Electronics. Inc. All right reserved.

Only for training and service purposes