LG KU730 Service Manual page 30

3. TECHNICAL BRIEF
3.5.5 UMTS transmit power detector (U105 : ADL5500)
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. ADL5500 is a mean-responding power detector for use in high
frequency receiver and transmitter signal chains from 100 MHz to 6GHz. It is easy to apply, requiring
only a single supply between 2.7V and 5.5V and a power supply decoupling capacitor. The input is
internally ac coupled and has a nominal input impedance of 50 Ohm. The output is a linear-responding
dc voltage with a conversion gain of 6.4V/Vrms at 900MHz. The on chip, 1kohm series resistance at
the output with an external shunt capacitor creates a low-pass filter response that reduce the residual
in the dc output voltage.
The ADL5500 is intended for true power measurement of simple and complex waveforms. The device
is particularly useful for measuring high crest factor (high peak-to-rms)signals, such as
CDMA,WCDMA and QPSK/QAM based OFDM waveforms. The KU730 uses ADL5500 power detector
IC. In Figure 3.5.5-1, Figure3.5.5-2 shows the output voltage versus PA output power of the ADL5500
setup as depicted in Figure3.5.5-1
Figure 3.5.5-1 Block diagram of ADL5500
Figure 3.5.5-2 Power detector response, Vout vs PA output power
- 31 -