LG 512W Service Manual page 14

C. RX I/Q Demodulator
The amplified IF signal at 45 MHz passes to the demodulator and is mixed down to DC to generate
I and Q BB signals. The BB signals pass via integrated low-pass filters to the BB A/D converters.
The remainder of the channel filtering is performed by the BB chipset. The demodulator contains
switches to maintain the sense of the BB I/Q outputs with respect to the incoming RF signal on both
GSM900 and DCS1800. It is not necessary to invert the receive data within the BB when switching
between 900MHz and 1800MHz. Fig. 3-2 shows RX path circuit.
Front End Module
Gain GSM
DCS
NF(dB) GSM
DCS
GSM, EGSM
DCS
Figure 3-2. RX Path Circuit.
Table 3-2. Gain and Noise Figure of RX Path.
LAN RF SAW Filter
-2.9 17
-3.5 16
1.5
1.8
Table 3-3. Total Gain and Noise Figure of RX Path.
Total Gain
28.3 dB
27.4 dB
- 13 -
3. TECHNICAL BRIEF
Mixerl
-2.8 9.5
-3.1 10.5
9.5
9.5
Total Noise Figure
IF SAW Filter Mixer2
-6.5 14
7
5.33 dB
6.62 dB