AD6659 Analog Devices, AD6659 Datasheet - Page 26

• Manufacturer Part Number: AD6659
• Description: Dual IF Receiver
• Manufacturer: Analog Devices

Specifications of AD6659

• Resolution (bits): 12bit
• # Chan: 2
• Sample Rate: 80MSPS
• Interface: Par
• Analog Input Type: Diff-Bip
• Ain Range: 2 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

NOISE SHAPING REQUANTIZER
The AD6659 features a noise shaping requantizer (NSR) to
allow higher than 12-bit SNR to be maintained in a subset of
the Nyquist band. Enabling and disabling the NSR mode is
controlled via Bit 0 in the 0x11E SPI register. In NSR mode,
the band of interest can be tuned using a low-pass, band-pass,
or high-pass filter setting via Bits[2:1] in the 0x11E SPI register.
20% BW NSR MODE (16 MHZ BW AT 80 MSPS)
NSR mode offers excellent noise performance over 20% of the
ADC sample rate (40% of Nyquist). The fundamental can be
tuned using a low-pass, band-pass, or high-pass filter by setting
the NSR Mode Bits[2:1] in the 0x11E SPI register.
Figure 45 to Figure 47 shows the typical spectrum that can be
expected from the AD6659 with the 20% BW NSR mode
enabled for the three different filter settings.
Figure 45. Low Pass NSR Mode: 7.5 MHz AIN @ 80 MSPS (16 MHz BW)
–105
–120
–135
–15
–30
–45
–60
–75
–90
0
0
4
+
8
12
80MSPS
7.5MHz @ –1dBFS
NSR LOW PASS MODE
SNR = 80.4dB (81.4dBFS) (IN-BAND)
SFDR = 96.5dBc (IN-BAND)
FREQUENCY (MHz)
2
16
20
3
24
28
4
32
6
36
5
40
Rev. | Page 26 of 40
Figure 46. Band-Pass NSR Mode: 19.7 MHz AIN @ 80 MSPS (16 MHz BW)
Figure 47. High Pass NSR Mode: 32 MHz AIN @ 80 MSPS (16 MHz BW)
–105
–120
–135
–105
–120
–135
–15
–30
–45
–60
–75
–90
–15
–30
–45
–60
–75
–90
0
0
0
0
5 +
80MSPS
19.7MHz @ –1dBFS
NSR BAND-PASS MODE
SNR = 80.3dB (81.3dBFS)
SFDR = 93.8dBc (IN-BAND)
4
80MSPS
32MHz @ –1dBFS
NSR HIGH PASS MODE
SNR = 80.4dB (81.4dBFS) (IN-BAND)
SFDR = 96.8dBc (IN-BAND)
(IN-BAND)
4
4
8
8
12
12
FREQUENCY (MHz)
FREQUENCY (MHz)
16
16
2
3
5
20
20
+
3
24
24
28
28
32
32
4
6
36
36
AD6659
6 2
40
40