AD6672 Analog Devices, AD6672 Datasheet - Page 21

• Manufacturer Part Number: AD6672
• Description: IF Receiver
• Manufacturer: Analog Devices

Specifications of AD6672

• Resolution (bits): 11bit
• # Chan: 1
• Sample Rate: 250MSPS
• Interface: LVDS
• Analog Input Type: Diff-Uni
• Ain Range: 1.75 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

NOISE SHAPING REQUANTIZER
The
allow more 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.
Two bandwidth (BW) modes are provided; the mode can be
selected from the SPI port. In each mode, the center frequency
of the band can be tuned such that IFs can be placed anywhere
in the Nyquist band.
22% BW NSR MODE (55 MHz BW AT 250 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 (Bits[3:1]) 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 (Bits[5:0]) in the NSR tuning register (Address 0x3E).
There are 57 possible tuning words (TW); each step is 0.5% of
the ADC sample rate. The following equations describe the left
band edge (f
edge (f
Figure 36 to Figure 38 show the typical spectrum that can be
expected from the
three tuning words.
AD6672
f
f
f
0
CENTER
1
–100
–120
–140
1
= f
= f
–20
–40
–60
–80
), respectively:
0
ADC
0
0
Figure 36. 22% Bandwidth Mode, Tuning Word = 13
+ 0.22 × f
250MSPS
180.1MHz @ –1.6BFS
SNR = 73.4dB (75.0dBFS)
SFDR = 92dBc (IN BAND)
= f
0
× 0.005 × TW
), the channel center (f
features a noise shaping requantizer (NSR) to
0
+ 0.11 × f
25
AD6672
ADC
ADC
FREQUENCY (MHz)
in the 22% bandwidth mode for
50
CENTER
75
), and the right band
100
125
Rev. 0 | Page 21 of 32
33% BW NSR MODE (>82 MHZ BW AT 250 MSPS)
The 33% bandwidth NSR mode offers excellent noise performance
over 33% of the ADC sample rate (66% of the Nyquist band).
The fundamental can be tuned using a low-pass, band-pass, or
high-pass filter by setting the NSR tuning word bits (Bits[5:0])
in Register 0x3E.
Figure 39 to Figure 41 show the typical spectrum that can be
expected from the
enabled for three filter settings.
–100
–120
–140
–100
–120
–140
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
Figure 37. 22% Bandwidth Mode, Tuning Word = 28
Figure 38. 22% Bandwidth Mode, Tuning Word = 41
250MSPS
180.1MHz @ –1.6BFS
SNR = 73.4dB (75.0dBFS)
SFDR = 93dBc (IN BAND)
250MSPS
180.1MHz @ –1.6BFS
SNR = 73.3dB (74.9dBFS)
SFDR = 92dBc (IN BAND)
25
25
AD6672
FREQUENCY (MHz)
FREQUENCY (MHz)
with the 33% bandwidth NSR mode
50
50
75
75
100
100
AD6672
125
125