Analog Devices ADRV9005 Reference Manual page 213

Reference Manual
RECEIVER DEMODULATOR
The receiver programmable FIR supports up to 128 taps. Each tap is 24 bits in width with the signed bit included. Four sets of customized FIR
profiles can be stored at the initialization phase. One of the four stored FIR profiles can be switched to load on the fly under the control of the
BBIC.
The receiver programmable FIR can be loaded with a customized low-pass filter profile to stop the adjacent channel interference, which helps
to achieve better channel selectivity. For example, as shown in
profile onto the receiver programmable FIR to perform common filtering. However, after the CFO is corrected through the carrier frequency
corrector block, a tight filter profile can be loaded to perform the deep channel selection filtering. The BBIC can initiate the change in the filter
profile on demand in the RF_Enabled state.
Frequency Discriminator
The frequency discriminator in rxnbdem translates the IQ signal into the frequency deviation (FD) signal, performing the frequency demodula-
tion in the digital domain. However, this module can be bypassed.
Figure 187 shows that the frequency discriminator outputs the transient frequency deviation (FD) and the transient squared magnitude (Mag2)
FD n = atan2 I n − D Q n − I n Q n − D , I n I n − D + Q n Q n − D
sample by sample. The output FD and the output Mag2 are defined as the following:
1
π
Mag2 n = I n + Q n
2
atan2 is same as the function in Octave.
where:
D is the programmable delay.
Typically, D is chosen as '1', which means 1 sampling clock delay.
Assuming the input IQ signal is the complex single tone, given by:
analog.com
Figure 186. Loose Filter Profile vs. Tight Filter Profile
Figure 187. Functional Diagram of Frequency Discriminator
2
Figure 186, before the CFO is corrected, the BBIC can program a loose filter
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