Panasonic EB-GD93, Technical Manual

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RECEIVER
Issue 1 Section 5 MCUK001001G8
Revision 0 – 16 – Technical Guide
5.3. Functional Description
5.3.1. Dual Band Receiver IC
The main building block for the Dual Band receiver is the Hatchi Bright III GSM transceiver IC (U104). The receiver is a
superheterodyne type with the 1st IF at 225 MHz and 2nd IF at 45 MHz. The intermediate frequencies are common to both
frequency bands.
The receiver section of U104 contains the following stages:
• Dual band LNA stage.
• Gain controlled 1st mixer for GSM 900 band.
• Gain controlled 1st mixer for GSM 1800 band.
• Gain controlled 2nd mixer.
• Gain controlled IF amplifier.
• I, Q quadrature down converter.
• Baseband operational amplifiers for further amplification and some filtering of the baseband I, Q signals.
5.3.2. Circuit Description
Figure 5.1: Dual Band Receiver
RF input to the receiver is either via the antenna or via the external antenna connector. The input signal from the antenna is
fed into the GSM 900 / GSM 1800 dual band Antenna switch module which comprises a diplexer and diode switches. The
diplexer splits the two GSM frequency bands whilst the pin switches route the signal flow from the receiver and the transmitter
as required.
The output is applied to the 1st dual band receiver SAW filter which provides the roofing filter for the Rx front end for both
900 MHz and 1800 MHz bands. Note that the apprpriate signal path will be set by the Antenna switching module. The output
is applied to the internal dual LNA of the Bright III IC.
The Bright III LNA gain is constant, typical gain is +17 dB for GSM 900 and +16 dB for GSM 1800, with a typical noise factor
of 1.5 dB and 1.7 dB respectively.
The output from the dual LNA passes through a dual LC filter which is designed to reduce interference at image spurious
frequency, and is fed into the 1st mixer of each band. Both 1st mixers are gain controlled by 3-wire bus to (typically) between
+9.5 dB and -1.0 dB for GSM 900 and b8.5 dB and -4.0 dB for GSM 1800.
The 1st IF output at 225 MHz is filtered by the differential IF SAW filter to reduce adjacent channel interference before
application to the 2nd mixer. The use of differential filters eliminates the need for a balun transformer, providing some cost and
space advantage.
The 2nd mixer is also gain controlled by 3-wire bus between, typically, +13.0 dB and -3.0 dB. Gain switching is synchronised
with the 1st mixer. The 2nd mixer output at 45 MHz is filtered by an L-C network before it is applied to the IF amplifier.
The IF amplifier is gain controlled by 3-wire bus for AGC purposes. The gain can be adjusted between -29 dB and +69 dB in
2 dB steps.
PGC
1800
DUAL BAND
RX BPF
FL202
DUAL BAND TRANSCEIVER
(PART)
IF
SAW
1st
Mixer
2nd
Mixer
900
1800
900
LPF
Rx
Tx
Rx
Tx
Ext
Ant.
HPF
10221-1
DUAL BAND
Rx SAW
I
Q
Demodulator
U104
FL201 LNA
DIPLEXER
U104
FL700