Service Manual
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V
V
I
I
T
T
E
E
L
L
C
C
O
O
M
M
M
M
O
O
B
B
I
I
L
L
E
E
T
T
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E
C
C
H
H
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G
G
Y
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S
S
.
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A
A
.
.
dividing the Tx IF VCO output frequency by two.
4.2.2 Description of Rx Part Circuit
Cellular Receiver covers the RF frequency band of 869 ~ 894 MHz and the IF frequency of 85.38MHz.
The RF signal received is sent out to the Receiver MMIC/ LNA(U106) via a duplexer(F100) for
amplification and then, is sent out to the Receiver MMIC/ Down mixer(U106) through Rx RF SAW
filter(U107). Here, the RF signal is mixed with the VCO(U102) signal of 954.38 MHz ~979.38 MHz. IF
signal converted by the Receiver MMIC/ Down mixer(U106) are sent out to IF SAW Filter(U108), which
have a role to filter a wanted frequency. The signal that has passed the IF SAW filter(U108) is fed into
AGC AMP that is controlled by the power density modulation (PDM) signal of the MSM(U125) based on
the strength of received signal. This AGC AMP is tuned into the level corresponding to the input window of
the base band analog processor (RX_BBA, U109). The AGC AMP controls Rx power level within 85dB
dynamic range. The signal entered to RX_BBA(U109) is converted again to 1.2288 MHz base band signal.
To do second frequency conversion, the frequency synthesizer in RX_BBA (U109) generates frequency of
170.76MHz and these signals are divided by two in order to use the Rx IF LO signal. These signals are
used to convert RX IF signals to I/Q base band signal. I and Q base-band signals are respectively sent out
to the analog digital converter via a low pass filter.
Duplexer (F100)
The duplexer(F100) consists of the Rx bandpass filter (BPF) and the Tx BPF which have the function of
separating Tx and Rx signals in the full duplex system for using the common antenna. The Tx 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. Its main function limits the bandwidth
of spectrum reaching the Receiver MMIC/ LNA(U106) and attenuates receiver spurious response. As a
result, the frequency sensitivity and selectivity of mobile phone increase.
Receiver MMIC/ LNA (U106)/ Down Mixer (U106)
- LNA : The characteristics of Low Noise Amplifier (LNA, U106) are low noise figure, high gain, high
intercept point and high reverse isolation. The frequency selectivity characteristic of mobile phone is
mostly determined by LNA(U106).
- The Down Mixer(U106) performs frequency translation by multiplying two signals. The
downconversion mixer employed in the Rx path has two distinctly different inputs, which are RF and
Local Oscillator (LO) signal. The RF signal is downconverted to IF signal by the local oscillator.
Rx RF SAW Filter (U107)
The main function of Rx RF SAW filter(U107) is to attenuate mobile phone spurious frequency, attenuate
direct IF frequency pick up, attenuate noise at the image frequency originating in or amplified by the
LNA(U106) and suppress second harmonic originated in the LNA(U106). The Rx RF SAW filter(U107) is
usually called image filter.