3.5.4 Thermistor (R135)
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 KU950.
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 KU950 uses National Semiconductor ADL5500 power detector IC. In
Figure 3.5.5-1, R129 is set to 68ohm&Coupler 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 ADL5500 setup as depicted in Figure3.5.5-1
3. TECHNICAL BRIEF
- 30 -
Figure 3.5.5-1 Block diagram of ADL5500 with resistive tap
Figure 3.5.5-2 Power detector response, Vout vs PA output power
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