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3. TECHNICAL BRIEF
A. RF front end
The RF receive signals(GSM 925MHz ~ 960MHz, DCS 1805MHz ~ 1880MHz) are input via the
antenna or coaxial connector. An antenna matching circuit is between the antenna and the
connector.
The FEM(FL301) is used to control the Rx and TX paths. And, the input signals VC1 and VC2 of a
FL301 are connected to 2-Input AND Gates(U306,U307) to switch either TX or RX path on. When
the RX path is turned on, the received RF signal then feeds either LNA(DCS) or LNA(DCS) path
selected by GSM-RX and DCS-RX respectively. This LNA(GSM) path contains one SAW filter,
contained within the FEM(FL301) to filter any unwanted signal apart from the DCS RX band. And,
the LNA(DCS) path is the same case.
Front-end module (LMZ0115-2A) contains an antenna switch module for dual band phone and dual
RF SAW filters. The logic and current is given below Table 3-1.
GSM TX
DCS TX
GSM/DCS RX
These two paths are then connected to the GSMB (#6) and DCSB (#10) of HD155128TF (U301),
respectively. The RF receive signal is amplified by LNAs in HD155128TF with the output at GSMC
(#4) and DCSC (#8) respectively, and then pass through the SAW filters B4121 (FL302) and B4133
(FL303).
After this filtering process, the signal then feeds into the first receiver mixer within the HD155128TF
(U301) for mixing with LO, which is produced by the synthesizer Si4133G_XM2 (U302). The mixers
are implemented as Gilbert cells and the first receiver mixer block contains four mixer cells whose
outputs are combined at the MIX1OUT/OUTB pins. The four mixer cells provide high or low
conversion gain at 900MHz or 1800MHz. The two high-gain cells have been optimized for to meet
the System requirements of the receiver at 900MHz and 1800MHz respectively.
On both bands, the gain step between high and low gain operation is around 12dB.
B. IF Part
In U301, UHF mixers produce an IF signal of frequency 225MHz at MIX1OUT (#49) and
MIX1OUTB (#50) in differential mode. This differential signal is filtered by MKFC225 (FL304), a 225
MHz SAW filter, and then fed to U301 IFIN and IFINB (#40 and #41).
The filtered IF signal then feeds into the second receiver mixer within the HD155128TF (U301) for
mixing with a 270 MHz, which was derived from the synthesizer Si4133G_XM2 (U302), and
generates a 45 MHz IF signal.
The 45 MHz output from the second mixer is filtered and passes to the PGA. The gain of the PGA is
set by a 6-bit programming word supplied by the BB. A further two bits are used to control
independently the gain steps in the first receive mixer and the IF amplifier/second mixer. The PGA
gain step size is nominally 2dB and the usable control range is 96 dB.
Table 3-1. The Logic and Current
VC1
2.7 V
0 V
0 V
- 12 -
VC2
0 V
10.0 mA max
2.7 V
10.0 mA max
0 V
Current
< 0.1 mA
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