LG MX8550, Service Manual

Page: 29 / 190

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M X8550
1.2 Description of RX Part Circuit
1.2.1 Diplexer (F105)
The main function of Diplexer is to prohibit the other band signals from flowing into the one band circuit and vice
versa. RF designer can use common tri-band antenna regardless of frequency band (800, 1575 and 1900 MHz). The
specification of VX8550 Diplexer is described below:
-30 to +85 deg Temperature Range
18 dB Min
(to Cellular) 18 dB Min
(to PCS)
Isolation
0.6 dB Max
(At +25 deg)
0.5 dB Max
(At +25 deg)
Insertion Loss to
Common
1850 – 1990 MHz 824 – 894 MHz Frequency Range
PCS Cellular
1.2.2 Duplexer (DP100, DP101)
The duplexer consists of the RX bandpass filter (BPF) and the TX BPF which has the function of separating TX and
RX signals in the full duplex system for using the common antenna. The TX part BPF is used to suppress noises and
spurious out of the TX frequency band. The RX BPF is used to receive only RX signal coming from the antenna,
which is usually called preselector. It’s main function is to limit the bandwidth of spectrum reaching the LNA and
mixer, attenuate receiver spurious response and suppress local oscillator energy. As a result frequency sensitivity and
selectivity of mobile phone increase. The specification of VX8550 duplexer described below ;
z
PCS duplexer:
54dB (1850~1910MHz)
45dB (1930~1990MHz)
52dB min
(1850~1910MHz)
43dB min (1930~1990MHz) Attenuation
9.5dB min 9.5dB min Return Loss
3.0dB max 3.5dB max Insertion Loss
1930~1990 MHz 1850~1910 MHz Pass Band
TX to RX (min) RX TX
z
Cellular duplexer
55dB (824~849MHz)
47dB (869~894MHz)
54dB min (824~849MHz) 45dB min (869~894MHz) Attenuation
8dB min 9dB min Return Loss
3.5dB max 2.3B max Insertion Loss
869~894 MHz 824~849 MHz Pass Band
TX to RX (min) RX TX
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