AD6677EBZ datasheet(23/48 Pages) AD

23 / 48 page

Data Sheet

AD6677

Rev. C | Page 23 of 48

NOISE SHAPING REQUANTIZER

The AD6677 features a NSR to allow higher than 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 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% BANDWIDTH 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 bit in the NSR control

range can be set using the 6-bit tuning word in the NSR tuning

words 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 (f0), the

channel center (fCENTER), and the right band edge (f1),

respectively:

f0 = fADC × 0.005 × TW

fCENTER = f0 + 0.11 × fADC

f1 = f0 + 0.22 × fADC

Figure 45 to Figure 47 show the typical spectrum that can be

expected from the AD6677 in the 22% bandwidth mode for

three different tuning words.

–140

–120

–100

–80

–60

–40

–20

100

125

FREQUENCY (Hz)

250MSPS

180.1MHz AT –1.6dBFS

SNR = 72.8dB (74.4dBFS)

SFDR = 92dBc (IN-BAND)

Figure 45. 22% Bandwidth Mode, Tuning Word = 13

–140

–120

–100

–80

–60

–40

–20

100

125

FREQUENCY (Hz)

250MSPS

180.1MHz AT –1.6dBFS

SNR = 72.9dB (74.5dBFS)

SFDR = 88dBc (IN-BAND)

Figure 46. 22% Bandwidth Mode, Tuning Word = 28 (fS/4 Tuning)

–140

–120

–100

–80

–60

–40

–20

100

125

FREQUENCY (Hz)

250MSPS

180.1MHz AT –1.6dBFS

SNR = 72.9dB (74.5dBFS)

SFDR = 87dBc (IN-BAND)

Figure 47. 22% Bandwidth Mode, Tuning Word = 41

AD6677EBZ датащи(PDF) 23 Page - Analog Devices

AD6677EBZ датащи(HTML) 23 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

датащи скачать

ссылки URL