AD6674 datasheet(59/97 Pages) AD

59 / 97 page

AD6674

Data Sheet

Rev. C | Page 58 of 96

Two different bandwidth modes are provided; select the mode

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. The NSR feature is enabled by default on

the AD6674. 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 (>75 MHz at 375 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, set the useful frequency range 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.

f0 = fADC × 0.005 × TW

where:

f0 is the left band edge.

fADC is the ADC sample rate.

TW is the tuning word.

fCENTER = f0 + 0.105 × fADC

where fCENTER is the channel center.

f1 = f0 + 0.21 × fADC

where f1 is the right band edge.

Figure 113 to Figure 115 show the typical spectrum that can be

expected from the AD6674 in the 21% BW mode for three

different tuning words.

–140

–20

–40

–60

–80

–100

–120

FREQUENCY (MHz)

AIN = −1dBFS

SNR = 74.0dBFS

ENOB = 11.8 BITS

SFDR = 92dBFS

BUFFER ONTROL 1 = 1.5×

175

150

125

100

Figure 113. AD6674-750, fCLOCK = 750 MHz, fS = 375 MSPS, fIN = 10.3 MHz,

21% BW Mode, Tuning Word = 0

–140

–20

–40

–60

–80

–100

–120

175

150

125

100

FREQUENCY (MHz)

AIN = −1dBFS

SNR = 74.0dBFS

ENOB = 11.8 BITS

SFDR = 95dBFS

BUFFER ONTROL 1 = 1.5×

Figure 114. AD6674-750, fCLOCK = 750 MHz, fS = 375 MSPS, fIN = 90.3 MHz,

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

–140

–20

–40

–60

–80

–100

–120

175

150

125

100

FREQUENCY (MHz)

AIN = −1dBFS

SNR = 73.9dBFS

ENOB = 11.9 BITS

SFDR = 93dBFS

BUFFER CONTROL 1 = 1.5×

Figure 115. AD6674-750, fCLOCK = 750 MHz, fS = 375 MSPS, fIN = 140.3 MHz,

21% BW Mode, Tuning Word = 58

28% BW Mode (>100 MHz at 375 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.

f0 = fADC × 0.005 × TW

where:

f0 is the left band edge.

fADC is the ADC sample rate.

TW is the tuning word.

fCENTER = f0 + 0.14 × fADC

where fCENTER is the channel center.

f1 = f0 + 0.28 × fADC

where f1 is the right band edge.

AD6674 Datasheet(PDF) 59 Page - Analog Devices

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