LG-TM250
which RF input terminal and internal interface circuit are integrated onto one IC after going through the GaAs
HBT (heterojunction bipolar transistor) process. The module of power amplifier is made up of an output end
interface circuit including this MMIC. The maximum power that can be inputted through the input terminal is
+7dBm and conversion gain is about 28dB. RF transmit signals that have been amplified through the power
amplifier are sent to the duplexer.
1.4 Description of Frequency Synthesizer Circuit
1.4.1 Voltage Control Temperature Compensation Crystal Oscillator (VCTCXO, U141)
The temperature variation of mobile phone can be compensated by TCXO. The reference frequency of a
mobile phone is -30~+85
°
C. The receives frequency tuning signals called TRK_LO_ADJ from MSM as
0.5V~2.5V DC via R and C filter in order to generate the reference frequency of 19.2 MHz and input it into the
frequency synthesizer. Frequency stability depending on temperature is
±
2.0 ppm.
1.4.2 Voltage Controlled Oscillator (VCO, U140)
The external VCO signal is processed by the LO generation and distribution circuits in RFR6000 to create the
PCS and Cellular quadrature downconverter’s LO signals. Likewise, the internal VCO signal of RFR6000 is
processed to create the GPS quadrature downconverter’s LO signal. In all cases, the LO signals applied at the
mixer ports are at the frequency different than the VCO frequency. This assures that the VCO frequency is
different than the RF frequency, an important consideration for Zero-IF processing. The VCO frequency used
are 1715.56~1768.89 MHz for PCS and 1738.08~1787.94 MHz for cellular and they are produced in single
voltage controlled oscillator of U140.
LG Electronics Inc.
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