Analog Devices ADRV9002

Preliminary Technical Data UG-1828
Rev. PrB | Page 165 of 277
Carrier Frequency Corrector (CFC)
Carrier Frequency Corrector in rxnbdem is to remove the carrier frequency offset. This module can be bypassed.
In a communication system, a desired signal is transmitted by the transmitter at RF over the air. Since the clock reference at the
transmitter and the receiver are independent, this may result in the RF carrier frequency offset between the transmitter and the receiver.
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, must 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
–20
–40
–
60
–100
–80
–120
–30
–20 –10 0 10 20 30
dBc
MHz
0
–
20
–40
–60
–
100
–80
–120
–30 –20 –10 0 10 20 30
dBc
MHz
–20MHz CW Fs/16 CW
0
–20
–40
–60
–100
–80
–120
–30 –20 –10 0 10 20 30
dBc
MHz
0
–20
–40
–60
–100
–80
–120
–30 –20 –10 0 10 20 30
dBc
MHz
Fs/8 CW Fs/4 CW
X = –22
Y = –2.388
24159-128
Figure 155. Output Spectrum of the CFC/NCO as f
S
= 61.44 MHz
Figure 154 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 154, the NCO output
spurs are −100 dBc below desired tone across the range of [−f
S
/2, f
S
/2]:
• −20 MHz CW,
•
CW,
•
CW, and
•
CW.
Please note these are not within the range defined above.