LG U310 Service Manual page 29

3. TECHNICAL BRIEF
3.5.4 Thermistor (R1032)
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 U310.
3.5.5 UMTS transmit power detector (U1003)
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 U310 uses National Semiconductor LMV228TLX power detector IC. In Figure 3.5.5-1, Directional
coupler is set to 18dB tab coupling. 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 LMV228TLX setup as
depicted in Figure1.5.5-1
Figure 3.5.5-1 Block diagram of LMV228TLX Typical Application
Figure 3.5.5-2 Power detector response, Vout vs PA output power
- 30 -