Analog Devices ADRV9001 User Manual page 150

UG-1828
This frequency difference is named by the carrier frequency offset (CFO). The CFC in rxnbdem enables the BBIC to remove the CFO
before the channel selection filtering at the receiver side. The correction value applied to the CFC, needs to be estimated and further
input by the BBIC. The change of the correction value may occur immediately or relative to RX frame boundary.
The CFC is implemented as a Digital Down Converter (DDC), which consists of an NCO and a complex multiplier in the datapath. As
the correction value, the NCO frequency word should be in the range of min (±20k,20% of sample rate).
0
X = –22
Y = –2.388
–20
–40
–60
–80
–100
–120
–30 –20
0
–20
–40
–60
–80
–100
–120
–30 –20
Figure 127 presents the spectrum of desired tone and the generated NCO spurs levels relative to desired tone for the CFC NCO at 61.44
MHz sampling frequency. The outlined plots show a typical case and some worst cases. As shown in Figure 127, the NCO output spurs
are -100 dBc below desired tone across the range of [-fs/2, fs/2]:
• −20 MHz CW,
• CW,
• CW, and
• CW.
Please note these are not within the range defined above.
Rx Programmable FIR Filter
Rx Programmable FIR Filter in rxnbdem is multi-functional and customizable. This module can be bypassed.
The Rx Programmable FIR supports up to 128 taps. Each tap is 24 bits width with the signed bit included. 4 sets of customized FIR
profiles can be stored at the initialization phase. One of the 4 stored FIR profiles can be switched to be loaded on the fly under the control
of the BBIC.
The Rx programmable FIR can be loaded a customized lowpass filter profile to stop the adjacent channel interference, which is helpful to
achieve better channel selectivity. For example, as shown in Figure 128, before the CFO is corrected, the BBIC may program a loose filter
–20MHz CW
–10 0 10 20
MHz
Fs/8 CW
–10 0 10 20
MHz
Figure 127. Output Spectrum of the CFC/NCO as Fs = 61.44 MHz
Rev. PrA | Page 150 of 253
0
–20
–40
–60
–80
–100
–120
30 –30 –20 –10
0
–20
–40
–60
–80
–100
–120
30 –30 –20 –10
Preliminary Technical Data
Fs/16 CW
0 10 20
MHz
Fs/4 CW
0 10 20
MHz
30
30