AD6657ABBCZ AD [Analog Devices], AD6657ABBCZ Datasheet - Page 25

• Manufacturer Part Number: AD6657ABBCZ
• Description: Quad IF Receiver
• Manufacturer: AD [Analog Devices]

Data Sheet
NOISE SHAPING REQUANTIZER
The
higher than an 11-bit SNR to be maintained in a subset of the
Nyquist band. The harmonic performance of the receiver is
unaffected by the NSR feature.
When enabled, the NSR contributes an additional 0.6 dB of
loss to the input signal, such that a 0 dBFS input is reduced to
−0.6 dBFS at the output pins.
The NSR feature can be independently controlled per channel
via the SPI or via the MODE pin.
Two different bandwidth modes are provided; the mode can be
selected from the SPI port. In each of the two modes, the center
frequency of the band can be tuned such that IFs can be placed
anywhere in the Nyquist band.
22% BW MODE (>40 MHZ at 184.32 MSPS)
The first bandwidth mode offers excellent noise performance
over 22% of the ADC sample rate (44% of the Nyquist band)
and can be centered by setting the NSR mode bits in the NSR
control register (Address 0x3C) to 000. In this mode, the useful
frequency range can be set using the 6-bit tuning word in the
NSR tuning word register (Address 0x3E).
There are 57 possible tuning words (TW); each step is 0.5% of
the ADC sample rate. The following three equations describe
the left band edge (f
band edge (f
AD6657A
f
f
f
0
CENTER
1
= f
= f
ADC
0
+ 0.22 × f
= f
1
× .005 × TW
), respectively.
0
features a noise shaping requantizer (NSR) to allow
+ 0.11 × f
0
ADC
), the channel center (f
ADC
CENTER
), and the right
Rev. 0 | Page 25 of 36
Figure 51 to Figure 53 show the typical spectrum that can be
expected from the
different tuning words.
–100
–120
–140
–100
–120
–140
–100
–120
–140
–20
–40
–60
–80
–20
–40
–60
–80
–20
–40
–60
–80
0
0
Figure 52. 22% BW Mode, Tuning Word = 28 (f
0
0
0
0
9.25 18.50 27.75 37.00 46.25 55.50 64.75 74.00 83.25 92.50
9.25 18.50 27.75 37.00 46.25 55.50 64.75 74.00 83.25 92.50
9.25 18.50 27.75 37.00 46.25 55.50 64.75 74.00 83.25 92.50
Figure 51. 22% BW Mode, Tuning Word = 13
Figure 53. 22% BW Mode, Tuning Word = 41
AD6657A
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (MHz)
in the 22% BW mode for three
THIRD HARMONIC
THIRD HARMONIC
THIRD HARMONIC
185MSPS
140.3MHz @ –1dBFS
NSR 22% BW MODE, TW = 13
SNR = 73.4dB (75.0dBFS)
SFDR = 91dBc
185MSPS
140.3MHz @ –1dBFS
NSR 22% BW MODE, TW = 28
SNR = 73.4dB (75.0dBFS)
SFDR = 91dBc
185MSPS
140.3MHz @ –1dBFS
NSR 22% BW MODE, TW = 41
SNR = 73.4dB (75.0dBFS)
SFDR = 91dBc
S
/4 Tuning)
AD6657A