AD6643 Analog Devices, AD6643 Datasheet - Page 25

• Manufacturer Part Number: AD6643
• Description: Dual IF Receiver
• Manufacturer: Analog Devices

Data Sheet
33% BW MODE (>60 MHZ AT 184.32 MSPS)
The second bandwidth mode offers excellent noise performance
over 33% of the ADC sample rate (66% of the Nyquist band)
and can be centered by setting the NSR mode bits in the NSR
control register (Address 0x3C) to 001. In this mode, the useful
frequency range can be set using the 6-bit tuning word in the
NSR tuning register (Address 0x3E). There are 34 possible
tuning words (TW); each step is 0.5% of the ADC sample rate.
The following three equations describe the left band edge (f
the channel center (f
respectively:
Figure 42 to Figure 44 show the typical spectrum that can be
expected from the AD6643 in the 33% BW mode for three
different tuning words.
f
f
f
0
CENTER
1
–100
–120
–140
= f
= f
–20
–40
–60
–80
0
ADC
0
0
+ 0.33 × f
= f
× .005 × TW
0
Figure 42. 33% BW Mode, Tuning Word = 5
10
+ 0.165 × f
20
ADC
CENTER
30
), and the right band edge (f
ADC
FREQUENCY (MHz)
40
50
200MSPS
140.1MHz @ –1.6dBFS
SNR = 71.3dB (72.9dBFS)
SFDR = 86dBc (IN BAND)
60
70
80
1
),
90
0
),
Rev. A | Page 25 of 36
–100
–120
–140
–100
–120
–140
–20
–40
–60
–80
–20
–40
–60
–80
Figure 43. 33% BW Mode, Tuning Word = 17 (f
0
0
0
0
Figure 44. 33% BW Mode, Tuning Word = 27
10
10
20
20
30
30
FREQUENCY (MHz)
FREQUENCY (MHz)
40
40
50
50
200MSPS
140.1MHz @ –1.6dBFS
SNR = 71.4dB (73dBFS)
SFDR = 86dBc (IN BAND)
200MSPS
140.1MHz @ –1.6dBFS
SNR = 71.2dB (72.8dBFS)
SFDR = 86dBc (IN BAND)
60
60
70
70
S
/4 Tuning)
80
80
AD6643
90
90