FLY E185
Service Manual
CKT Confidential
Page 9 of 47
Figure 3.2.1 GSM RF circuit
From the chart we can see that the RF part is mainly composed of a highly integrated
CMOS transceiver chip (AD6548), some RX Saw filters, reference crystal oscillator,
power amplifier/antenna switch module (2in1), antenna and the matching components
between each other.
3.2.2
Analog Front-end& Analog Blocks
3.2.2.1 Baseband Front End
Baseband Front End is a modem interface between TX/RX mixed-signal modules and digital
signal processor (DSP). We can divide this block into two parts (see Figure 138). The first is the
uplink (transmitting) path, which converts bit-stream from DSP into digital in-phase (I) and
quadrature (Q) signals for TX mixed-signal module. The second part is the downlink (receiving)
path, which receives digital in-phase (I) and quadrature (Q) signals from RX mixed-signal module,
performs FIR filtering and then sends results to DSP. Figure 138illustrates interconnection around
Baseband Front End. In the figure the shadowed blocks compose Baseband Front End.
To enhance the capability of data processing of mobile phone and base station, the Enhanced Data
for GSM Evolution (EDGE), which used 8PSK Modulationrather than GMSK Modulation in
GSM system may provide the triple data transmission rate of 384 kbps for system to supply the
solution of voice, data, Internet linkage, and other kinds of mutual linkage, while 3bits per
symbols in 8PSK Modulation and 1 bit per symbol in GMSK Modulation.
The uplink path is mainly composed of GMSK Modulator or 8PSK Modulator and uplink parts of
Baseband Serial Ports, and the downlink path is mainly composed of RX digital FIR filter and
downlink parts of Baseband Serial Ports. Baseband Serial Ports is a serial interface used to
communicate with DSP. In addition, there is a set of control registers in Baseband Front End that
is intended for control of TX/RX mixed-signal modules, inclusive of several compensation circuit:
calibration of I/Q DC offset, I/Q Quadrature Phase Compensation and I/Q Gain Mismatch of
