Samsung SGH-X490 Service Manual

Also see for SGH-X490: User manual User guide

Samsung SGH-X490 Service Manual Manual pdf 5 page image

SAMSUNG Proprietary-Contents may change without notice2-1. SGH-X490 RF Circuit Description2-1-1. RX PART- ASM(U100) Switching Tx, Rx path for GSM900, DCS1800, PCS1900 by logic controlling.- ASM Control Logic (U100) Truth TableVC1 VC2 VC3Tx Mode (GSM900) H L LTx Mode (DCS1800/1900) L H LRx Mode (GSM900) L L LRx Mode (DCS1800) L L LRx Mode (PCS1900) L L H- FILTERTo convert Electromagnetic Field Wave to Acoustic Wave and then pass the specific frequency band.- GSM FILTER (F101) For filtering the frequency band between 925 and 960 MHz- DCS FILTER (F102) For filtering the frequency band between 1805 and 1880 MHz.- PCS FILTER (F100) For filtering the frequency band between 1930 and 1990 MHz.- VC-TCXO (OSC101)This module generates the 26MHz reference clock to drive the logic and RF. After division by two a reference clock of13MHz is supplied to the other parts of the system through the pin CLKOUT. After additional process, the referenceclock applies to the U100 Rx IQ demodulator and Tx IQ modulator. And then, the oscillator is controlled by serial datato select channel and use fast lock mode for GPRS high class operation.- Transceiver (U101)The receiver front-end which amplifies the GSM, DCS, PCS aerial signal, converts the chosen channel down to a low IFsignal of 100 kHz. The first stages are symmetrical low noise amplifiers (LNAs). The LNAs are followed by an IQ downmixer. It consists of two mixers in parallel but driven by quadrature out of phase LO signals. The In phase (I) andQuadrature phase (Q) IF signals are low pass filtered to provide protection from high frequency offset interferes. The lowIF I and Q signals are then fed into the channel filter. The front-end low IF I and Q outputs enter the integratedbandpass channel filter with provision for five 8 dB gain steps in front of the filter.2-1-2. TX PARTI and Q baseband signals are applied to the IQ modulator that shifts the modulation spectrum up to the transmit IF. It isdesigned for low harmonic distortion, low carrier leakage and high image rejection to keep the phase error as small aspossible.