Circuit Description - Samsung SGH-X480 Service Manual

2 . C i r c u i t D e s c r i p t i o n
1. SGH-X480, SGH-X480C, SGH-X488 RF Circuit Description
1) RX PART
1. ASM(F900) ¡æ Switching Tx, Rx path for GSM900, DCS1800 and PCS1900 by logic controlling.
2. ASM Control Logic Truth Table
Tx (GSM900)
Tx (DCS1800/ PCS1900)
Rx (GSM900)
Rx (DCS1800)
Rx (PCS 1900)
3. Saw FILTER
To convert Electromagnetic Field Wave to Acoustic Wave and then pass the specific frequency band.
- GSM FILTER (F800) ¡æ For filtering the frequency band between 925 and 960 MHz.
- DCS FILTER (F800) ¡æ For filtering the frequency band between 1805 and 1880 MHz
- PCS FILTER (F801) ¡æ For filtering the frequency band between 1930 and 1990 MHz.
4. Crystal (U802)
To generate the 26MHz reference clock to drive the logic and RF.
After additional process, the reference clock applies to the U801 Rx IQ demodulator and Tx IQ modulator.
The oscillator for RX IQ demodulator and Tx modulator are controlled by serial data to select channel and use fast lock
mode for GPRS high class operation.
5. Si4210 (U801)
The receive section integrates four differential-input low noise amplifiers LNAs supporting the GSM850, EGSM900,
DCS1800 and PCS1900 bands. The LNA inputs are matched to the 150 ohm balanced-output SAW filters through externa
LC matching network.
A quadrature Image-reject mixer downconverts the RF signal to a 200 KHz intermediate frequency(IF). The mixer output is
amplified with an analog programmable gain amplifier(PGA) that is controlled with the AGAIN. The quadrature IF ? ?
is digitized with high resolution analog-to-digital converts (ADC).
The ADC output is downconverted to baseband with a digital quadrature LO signal. Digital decimation and FIR filters
perform digital filtering and remove ADC quantization noise, blockers and reference interferers.
After filtering, the digital output is scaled with a digital PGA, which is controlled with the DGAIN. DACs drive a
differential I and Q analog signal onto the BIP, BIN, BQP and BQN pins to interface to standard analog-input baseband
ICs.
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