LG L601i Service Manual page 28

3. TECHNICAL BRIEF
3.5.3 UMTS Power Amplifier (U606)
The AWT6277 meets the increasing demands for higher output power in UMTS handsets. The PA
module is optimized for VREF = +2.85 V, a requirement for compatibility with the Qualcomm® 6250
chipset. The device is manufactured on an advanced InGaP HBT MMIC technology offering state-of-
the-art reliability, temperature stability, and ruggedness. Selectable bias modes that optimize efficiency
for different output power levels, and a shutdown mode with low leakage current, increase handset talk
and standby time. The self-contained 4 mm x 4 mm x 1.1 mm surface mount package incorporates
matching networks optimized for output power, efficiency, and linearity in a 50 Ω system.
Figure3.5.3-1 UMTS PA functional block diagram
3.5.4 Thermistor (RT100)
This thermistor senses temperature variations around UMTS PA to adjust PA gain deviation for assure
compliance with the applicable transmit power control standards. Negative temperature compensation
thermistor is used in the L601i.
3.5.5 UMTS transmit power detector (U106)
This detector couples PA output power level to calibrate the transmitter characteristic over the channel
variation and temperature. Its detector coupling range and converted voltage is based on diode
sensitivity and transmitter power level. The L601i uses National Semiconductor LMV225TLX power
detector IC. In Figure 3.5.5-1, R1 is set to 1.8kΩ resulting in an attenuation of 31.4dB. The output
voltage is proportional to the logarithm of the input power. Figure3.5.5-2 shows the output voltage
versus PA output power of the LMV225TLX setup as depicted in Figure3.5.5-1
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