H/W Circuit Description; Rf Transceiver General Description; Receiver Part - LG L1100 Service Manual

3. H/W Circuit Description

3.1 RF Transceiver General Description

The RF parts consist of a transceiver part, a power amplifier part, a front-end module part, a voltage
supply part, and a VC-TCXO part.
The Aero TM I transceiver is composed of single RF chipset, Si4205-BM[U803] which is a triple and
quad-band GSM/GPRS wireless communications.
This device integrated a receiver based on a low IF (100KHz) architecture and a transmitter based on
modulation loop architecture. 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 Si4205-BM[U803] integrates three differential
input LNAs that are matched to the 150 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 from the frequency synthesizer. 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 Si4205-BM[U803] 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
4 → 3
3 → 2
2 → 1
1 → 0
-12-
Rx Power (dBm)
-85dBm±
2dBm
-90dBm±
2dBm
-95dBm±
2dBm
-100dBm±
2dBm
-105dBm±
2dBm