AD9148BBCZ datasheet(52/73 Pages) AD

52 / 73 page

AD9148

Preliminary Technical Data

Rev. PrA | Page 52 of 73

Half-Band Filter 1 (HB1)

HB1 has four modes of operation, as shown in Figure 63. The

shape of the filter response is identical in each of the four modes.

The four modes are distinguished by two factors, the filter center

frequency and whether or not the input signal is modulated by

the filter.

–20

–40

–60

–80

–100

02.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

(×

fIN1)

MODE 0

MODE 1

MODE 3

MODE 2

Figure 63. HB1 Filter Modes

As is shown in Figure 63, the center frequency in each mode is

offset by ½ of the input data rate (fIN1) of the filter. Mode 0 and

Mode 1 do not modulate the input signal. Mode 2 and Mode 3

modulate the input signal by fIN1. When operating in Mode 0

and Mode 2, the I and Q paths operate independently and no

mixing of the data between channels occurs. When operating

in Mode 1 and Mode 3, mixing of the data between the I and Q

paths occurs; therefore, the data input into the filter is assumed

complex. Table 18 summarizes the HB1 modes.

Table 18. 2× Interpolation Filter Modes (Register 0x1C to

Interpolation

Factor

Filter Modes

fCENTER

(fDAC)

Pre Mod

HB1

HB2

HB3

Off

fDAC/4

Off

fDAC/2

Off

−fDAC/4

Figure 64 shows the pass-band filter response for HB1. 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 19 shows the pass-band flatness

and stop-band rejection the HB1 filter supports at different

bandwidths.

0.02

–0.10

–0.08

–0.06

–0.04

–0.02

00.40

0.36

0.32

0.28

0.24

0.20

0.16

0.12

0.08

0.04

(×

fIN1)

Figure 64. Pass-Band Detail of HB1

Table 19. HB1 Pass-Band and Stop-Band Performance by

Bandwidth

Bandwidth (% of fIN1)

Pass-Band

Flatness (dB)

Stop-Band

Rejection (dB)

0.001

80.4

0.0012

81.2

0.0033

82.0

0.0076

83.6

0.0271

85.6

0.1096

Half-Band Filter 2 (HB2)

HB2 has eight modes of operation, as shown in Figure 65 and

Figure 66. The shape of the filter response is identical in each of

the eight modes. The eight modes are distinguished by two factors,

the filter center frequency and whether the input signal is

modulated by the filter.

–20

–40

–60

–80

–100

02.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

(×

fIN2)

MODE 0

MODE 2

MODE 6

MODE 4

Figure 65. HB2, Even Filter Modes

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