TECHNICAL DESCRIPTION
Issue 1
Section 4
PMCD030901C8
Revision 0
– 12 –
Service Manual
4.3. Receiver
4.3.1
Functional Description
Figure 4.4: Receiver Block Diagram
The main building block for the receiver is the transceiver IC (U605) which includes a direct conversion receiver with I and Q
quadrature demodulation.
Received signals from the antenna are passed via the RF to the antenna switch module (front end module) FL600. This
module contains a diplexer which filters the signal to the required receiver path (EGSM 900 or GSM 1800 / GSM 1900). Pin
diode switches within FL600 route the signal path from the transmitter or to the receiver as required.
Internal SAW filters in FL600 provide attenuation of signals outside the required receive band which could degrade the signal-
to-noise ratio of wanted signals. There is a SAW filter for each of three receiver bands, EGSM 900, GSM 1800 and
GSM 1900.
The received signal is output to the port of FL600 and carried by a balanced pair of printed circuit tracks to the corresponding
frequency band LNA input of transceiver U603. Output from the LNA is then converted directly to baseband frequency by a
quadrature demodulator mixer.
The local oscillator (LO) signal presented to the mixer is provided by an internal VCO and is divided by 4 (EGSM 900) or by 2
(GSM 1800 and GSM 1900).
At baseband, the GSM signal is passed through a 1-pole blocking filter (comprising two external capacitors) and a channel
filter. These filters provide some attenuation to adjacent channel signals at the receiver input. An equaliser stage in the
baseband IC is used to correct any group delay variation which causes distortion of the received signal.
The baseband signal is then amplified by programmable variable gain amplifier (PGA) stages within U603. Combined with the
LNA these give a total gain between -2 dB and +85 dB.
The I and Q baseband signals are then offset to a DC offset level produced by U603 to 1.35 V. this offset level provides the
largest dynamic range available for the receiver, which is limited by SYREN baseband IC. SYREN provides analogue to digital
conversion of the demodulated signal and also some further 45dB attenuation to adjacent channel interference through DSP
filtering.
10698-1
Rx
EGSM 900
GSM 1900
GSM 1800
HPF
LPF
Rx
Tx
Rx
Tx
FL600
SWITCH
MODULE
IR
IRX
QR
QRX
BASEBAND
AMPLIFIERS
BASEBAND
FILTERS
U603
TRIPLE BAND TRANSCEIVER
PGC
AMP
RF
LO
LNA
Tx
LNA
LNA