Thermistor (Rt1000); Umts Transmit Power Detector (U1001) - LG U8500 Service Manual

3. TECHNICAL BRIEF

3.5.4 Thermistor (RT1000)

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 U8500.

3.5.5 UMTS transmit power detector (U1001)

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 U8500 uses National Semiconductor LMV225TLX power detector IC. In Figure 1.5.5-1, 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. Figure1.5.5-2 shows the output voltage versus PA output power of the LMV225TLX setup
as depicted in Figure1.5.5-1
Figure 3.5.5-1 Block diagram of LMV225TLX with high resistive tap
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