H/W Circuit Description; Rf Transceiver General Description; Receiver Part - LG MG810c Service Manual

3. H/W Circuit Description

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 VCTCXO part.
The SI4210[U401] 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 SI4210[U401] 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 SI4210[U401] 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
ICx.
Antenna Display
Antenna Bar Number
5
4
3
2
2
1
Table 3-1. Antenna(RSSI) Display
- 13 -
3. H/W Circuit Description
Rx Power (dBm)
≥-85
≥-90
≥-95
≥-100
≥-105
<-105