Samsung SGH-X600 Service Manual page 4

Gsm telephone

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2 . S G H - X 6 0 0

C i r c u i t

1. SGH-X600 RF Circuit Description

1) RX PART

1. ASM(U102) ¡æ Switching Tx, Rx path for GSM900, DCS1800 by logic controlling.

2. ASM Control Logic (Q100, Q101) ¡æ Truth Table

GSM Tx Mode

DCS Tx Mode

GSM Rx Mode

DCS Rx Mode

3. FILTER

To convert Electromagnetic Field Wave to Acoustic Wave and then pass the specific frequency band.

- GSM FILTER (F101) ¡æ For filtering the frequency band between 925 ~ 960 MHz

- DCS FILTER (F102) ¡æ For filtering the frequency band 1805 ~ 1880 MHz.

4. VC-TCXO (OSC101)

To generate the 26MHz reference clock to drive the logic and RF.

After additional process, the reference clock applies to the U103 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. Transceiver (U103)

The receiver front-end converts the aerial RF signal from EGSM, DCS bands down to a low intermediate frequency (IF)

of 100 kHz. The first stages are symmetrical low noise amplifiers (LNAs). They are matched to 50 ohm. The LNAs are

followed by an I,Q down mixer. It consists of two mixers in parallel but driven by quadrature out of phase LO signals.

The In phase (I) and quadrature phase (Q) IF signals are low pass filtered to provide protection from high frequency

offset interferers. The low IF I and Q signals are then fed into the channel filter. The front-end low IF I and Q outputs

enter the integrated bandpass channel filter with provision for five 8dB gain steps in front of the filters.

2) TX PART

Baseband IQ signal fed into offset PLL, this function is included inside of U103 chip.

OSC100 chip generates modulator signal which power level is about 6.5dBm and fed into Power Amplifier(U101).

The PA output power and power ramping are well controlled by Auto Power Control circuit.

We use offset PLL below .

D e s c r i p t i o n

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