AD9146 datasheet(33/52 Pages) AD

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AD9146

Rev. 0 | Page 33 of 52

.32

Table 18. HB2 Pass-Band and Stop-Band Performance by

Bandwidth

Bandwidth (% of fIN2)

Pass-Band

Flatness (dB)

Figure 44 shows the pass-band filter response for HB2. In most

applications, the usable bandwidth of the filter is limited by the

image suppression provided by the stop-band rejection and not

by the pass-band flatness. Table 18 shows the pass-band flatness

and stop-band rejection supported by the HB2 filter at different

bandwidths.

Stop-Band

Rejection (dB)

0.001

50.8

0.0012

0.02

–0.02

–0.04

–0.06

–0.08

–0.10

0.28

0.24

0.20

0.16

0.12

0.08

0.04

FREQUENCY (×

fIN2) (Hz)

52.8

0.0028

0.0089

0.0287

64.8

0.1877

DATAPATH CONFIGURATION

Configuring the AD9146 datapath starts with the application

requirements of the input data rate, the interpolation ratio, the

output signal bandwidth, and the output signal center frequency.

Given these four parameters, the first step in configuring the

datapath is to verify that the device supports the bandwidth

requirements. The modes of the interpolation filters are then

chosen.

DETERMINING INTERPOLATION FILTER MODES

Table 19 shows the recommended interpolation filter settings

for a variety of filter interpolation factors, filter center frequencies,

and signal modulation. The interpolation modes were chosen

based on the final center frequency of the signal and by deter-

mining the frequency shift of the signal required. When these

parameters are known and put in terms of the input data rate

(fDATA), the filter configuration that comes closest to matching

is selected from Table 19.

Figure 44. Pass-Band Detail of HB2

Table 19. Recommended Interpolation Filter Modes (Register 0x1C and Register 0x1D)

Interpolation Factor

Filter Modes

fSIGNAL Modulation

HB1[1:0]

HB2[5:0]

fCENTER Shift

00 (Mode 0)

000000

01 (Mode 1)

001001

DC1

fDATA/2

10 (Mode 2)

010010

fDATA

11 (Mode 3)

011011

fDATA1

3fDATA/2

00 (Mode 0)

100100

2fDATA

01 (Mode 1)

101101

2fDATA1

5fDATA/2

10 (Mode 2)

110110

3fDATA

11 (Mode 3)

111111

3fDATA1

7fDATA/2

00 (Mode 0)

Bypass

01 (Mode 1)

Bypass

DC1

fDATA/2

10 (Mode 2)

Bypass

fDATA

11 (Mode 3)

Bypass

fDATA1

3fDATA/2

1 When HB1 Mode 1 or Mode 3 is used, enabling premodulation provides an additional frequency translation of the input signal by fDATA/2, which centers a baseband

input signal in the filter pass band.

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