Technical Brief; Rf Transceiver General Description; Receiver Part - LG F1200 Service Manual

3. TECHNICAL BRIEF

3. TECHNICAL BRIEF

3.1 RF Transceiver General Description

The RF parts consist of a transmitter part, a receiver part, a frequency synthesizer part, a
voltage supply part, and a DCXO part.
The SI4206[U102] is a triple band transceiver IC suitable for GSM 900, DCS 1800 and PCS
1900 GPRS class 12 applications. This device integrated a receiver based on a low IF (100KHz)
architecture and a transmitter based on modulation loop architecture. And, the synthesizer part
are included in the IC, a complete dual band synthesizer with built in VCOs.
The transceiver employed a 3 wire serial interface to allow an external system controller to write
the control registers for dividers, receive path gain, power down setting, and other controls.

3.2 Receiver Part

The receiver part uses a low-IF receiver architecture that allows for the on-chip integration of the
channel selection filters, eliminating the external RF image reject filters and the IF SAW filter
required in conventional super-heterodyne architecture. The Si4206[U102] integrates three
differential input LNAs that are matched to the 200 Ohm balanced-output SAW filters through
external LC matching networks. A quadrature image-rejection mixer downconverts the RF signal
to a 100kHz intermediate frequency (IF) with the RFLO. The mixer output is amplified with an
analog programmable gain amplifier (PGA) and quadrature IF signal is digitized with high
resolution A/D converters (ADCs). The Si4206[U102] downconverts the ADC output to
baseband with a digital 100kHz quadrature LO signal. Digital decimation and IIR filters perform
channel selection to remove blocking and reference interference signals. After channel
selection, the digital output is scaled with digital PGA, which is controlled with the DGAIN[5:0]
bits in register 05h.The amplified digital output signal go through with DACs that drive a
differential analog signal onto the RXIP,RXIN,RXQP and RXQN pins to interface to standard
analog ADC input baseband ICs.
Antenna Display
Antenna Bar Number
5
4
3
2
2
1
Table 1. Antenna (RSSI) Display
- 12 -
Power (dBm)
≥ -85
≥ -90
≥ -95
≥ -100
≥ -105
< -105