FLY E185
Service Manual
uplink analog-to-digital (D/A) converters as well as I/Q Gain Mismatch for downlink
digital-to-analog (A/D) converters in TX/RX mixed-signal modules. The timing of bit streaming
through Baseband Front End is completely under control of TDMA timer. Usually only either of
uplink and downlink paths is active at one moment. However, both of the uplink and downlink
paths will be active simultaneously when Baseband Front End is in loopback mode.
When either of TX windows in TDMA timer is opened, the uplink path in Baseband Front End
will be activated. Accordingly components on the uplink path such as GMSK Modulator or 8PSK
Modulator will be powered on, and then TX mixed-signal module is also powered on. The sub
block Baseband Serial Ports will sink TX data bits from DSP and then forward them to GMSK
Modulator or 8PSK Modulator. The outputs from GMSK Modulator or 8PSK Modulator are sent
to TX mixed-signal module in format of I/Q signals. Finally D/A conversions are performed in TX
mixed-signal module and the output analog signal is output to RF module. Additionally, 8PSK
Modulation intrinsically extends the bursts window and reports in 8MVD (8PSK Modulation
Valid) in BFE_STA status register. Similarly, while either of RX windows in TDMA timer is
opened, the downlink path in Baseband Front End will be activated. Accordingly components on
the downlink path such as RX mixed-signal module and RX digital FIR filter are then powered on.
First A/D conversions are performed in RX mixed-signal module, and then the results in format of
I/Q signals are sourced to Low Pass Filtering with different bandwidth (Narrow one about Fc = 90
kHz, Wide one about FC = 110khz), Interference Detection Circuit to determine which Filter to be
used by judging receiving power on current burst, Additionally, “I/Q Compensation Circuit” is an
option in data path for modifying Receiving I/Q pair gain mismatch.. Finally the results will be
sourced to DSP through Baseband Serial Ports.
Block Diagram of Baseband Front End:
Figure 3.2.2.1
Baseband Front End Structure
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