AD6679 datasheet(57/81 Pages) AD

57 / 81 page

Data Sheet

AD6679

Rev. B | Page 57 of 81

of the band can be tuned such that IFs can be placed anywhere

in the Nyquist band. The NSR feature is enabled by default on

the AD6679. The bandwidth and mode of the NSR operation

are selected by setting the appropriate bits in Register 0x420 and

bits in these two registers, the NSR feature can be enabled for

the desired mode of operation.

21% BW Mode (>100 MHz at 491.52 MSPS)

The first NSR mode offers excellent noise performance across a

bandwidth that is 21% of the ADC output sample rate (42% of

the Nyquist band) and can be centered by setting the NSR mode

bits in the NSR mode register (Address 0x420) to 000. In this

mode, the useful frequency range can be set using the 6-bit

tuning word in the NSR tuning register (Address 0x422). There

are 59 possible tuning words (TW), from 0 to 58; each step is

0.5% of the ADC sample rate. The following three equations

describe the left band edge (f0), the channel center (fCENTER), and

the right band edge (f1), respectively:

f0 = fADC × 0.005 × TW

fCENTER = f0 + 0.105 × fADC

f1 = f0 + 0.21 × fADC

Figure 74 to Figure 76 show the typical spectrum that can be

expected from the AD6679 in the 21% BW mode for three

different tuning words.

–140

–120

–100

–80

–60

–40

–20

100

125

150

175

200

225

250

FREQUENCY (MHz)

AIN = −1dBFS

SNR = 75.2dBFS

ENOB = 11.6 BITS

SFDR = 87dBFS

BUFFER CONTROL 1 = 2.0×

Figure 74. 21% BW Mode, Tuning Word = 0

–140

–120

–100

–80

–60

–40

–20

100

125

150

175

200

225

250

FREQUENCY (MHz)

AIN = −1dBFS

SNR = 75.0dBFS

ENOB = 11.6 BITS

SFDR = 85dBFS

BUFFER CONTROL 1 = 2.0×

Figure 75. 21% BW Mode, Tuning Word = 26 (fS/4 Tuning)

–140

–120

–100

–80

–60

–40

–20

100

125

150

175

200

225

250

FREQUENCY (MHz)

AIN = −1dBFS

SNR = 74.9dBFS

ENOB = 11.6 BITS

SFDR = 90dBFS

BUFFER CONTROL 1 = 2.0×

Figure 76. 21% BW Mode, Tuning Word = 58

28% BW Mode (>130 MHz at 491.52 MSPS)

The second NSR mode offers excellent noise performance

across a bandwidth that is 28% of the ADC output sample rate

(56% of the Nyquist band) and can be centered by setting the

NSR mode bits in the NSR mode register (Address 0x420) to

001. In this mode, the useful frequency range can be set using

the 6-bit tuning word in the NSR tuning register (Address 0x422).

There are 44 possible tuning words (TW, from 0 to 43); each step is

0.5% of the ADC sample rate. The following three equations

describe the left band edge (f0), the channel center (fCENTER), and

the right band edge (f1), respectively:

f0 = fADC × 0.005 × TW

fCENTER = f0 + 0.14 × fADC

f1 = f0 + 0.28 × fADC

Figure 77 to Figure 79 show the typical spectrum that can be

expected from the AD6679 in the 28% BW mode for three

different tuning words.

AD6679 Datasheet(PDF) 57 Page - Analog Devices

AD6679 Datasheet(HTML) 57 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

Datasheet Download

Link URL