FLY E185
Service Manual
3.2.2.2 Downlink Path (RX Path)
On the downlink path, the sub-block between RX mixed-signal module and Baseband Serial Ports
is RX Path. It mainly consists of two parallel digital FIR filter with programmable tap number,
two sets of multiplexing paths for loopback modes, interface for RX mixed-signal module,
Interference Detection Circuit, I/Q Gain Mismatch compensation circuit, and interface for
Baseband Serial Ports. The block diagram is shown in Figure 140.
While RX enable windows are open, RX Path will issue control signals to have RX mixed-signal
module proceed to make A/D conversion. As each conversion is finished, one set of I/Q signals
will be latched. There exists a digital FIR filter for these I/Q signals. The result of filtering will be
dumped to Baseband Serial Ports whenever RX dump windows are opened.
Block Diagram of RX Path:
Figure3.2.2.2 downlink diagram
In order to compensate I/Q Gain Mismatch , configure IGAINSEL(I Gain Selection) in RX_CON
control register, the I over Q ratio can be compensate for 0.3 dB/step, totally 11 steps resulted in
dynamic range up to +/-1.5dB. The I/Q swap functionality can be setting “1” for SWAP(I/Q
Swapping) in RX_CFG control register, which is used to swap I/Q channel signals from RX
mixed-signal module before they are latched into RX digital FIR filter. It is intended to provide
flexibility for I/Q connection with RF modules.
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